aliens bash tutorial

original link: http://subsignal.org/doc/AliensBashTutorial.html
=========================== Aliens Bash Tutorial ==============================
————— Written by Billy Wideling <-> alien@koping.net —————-
===============================================================================

First you probably need to read a UNIX command bible to really understand this
tutorial, but I will try to make it as clear as possible, there is about
100-150 UNIX commands explained later in this tutorial.
You are to have some UNIX experance before starting on this tutorial, so
if you feel that you have UNIX/Linux experance feel free to start to learn
here.
What I included here is general shell scripting, most common other things
and some UNIX commands.
Here’s the most common shell types:

bash = Bourne again shell
sh    = shell
csh   = C shell
tcsh = Tenex C shell (not tab-completion-extended C shell)
tclsh = Tcl shell
ksh   = korn shell
ash   = a shell
bsh   = bourne shell ? (in most Linux distributions it’s a link to /bin/ash)
zsh   = the Z shell (it’s what it’s manual page tells about it .. :/ )

===============================================================================
1 – What you already know. (should know)
===============================================================================

Here we go, bash scripting is nothing more then combining lots of UNIX commands
to do things for you, you can even make simple games in bash
(just UNIX commands) or as in normal cases, batch files to control things
in your computer.

There is a variety of easyer and harder examples in the beginning of this
tutorial, I’ve done it this way to make it easier for people to get the
general picture, so they will get more of the “aha!” experiences in the later
chapters of this tutorial.

What bash or any scripting language does is to call for premade programs
that lives in your computer.
So when you write a command in a script you are calling a command that is
a part of the system.
That is why this tutorial will be just as much a Linux and UNIX tutorial
as a shell scripting tutorial.

I will however not take up much about The X Windows System in this
tutorial, for the simple reason that a Window Manager does nothing else
then display programs.

This means that a Window Manager is like a graphical shell for the system.
You can do all in this tutorial from any terminal emulator in a Linux
Graphical Enviorment (The X Windows System).
A terminal emulator would be such as: Eterm, xterm, axvt, rxvt, kterm etc.
A terminal emulator let’s you get up a terminal with a command prompt
in a graphical window.

——————————————————————————-

Shell command separator/control characters:

| = pipe will take the first commands stdout as the second commands stdin.
|| = OR if first command is false, it will take the second.
|= = OR IS (mostly used in if statements)
&& = AND if first command is true, it will execute the second one.
! = NOT (mostly used in if and test statements), but as a shell-command
     it opens a shell to run the command (ex. `! echo foo`)
!= = NOT IS (mostly used in if statements)
!$ = last commands last argument
!! = repeat last command
= = IS (mostly used in if statements)
; = will separate 2 commands as if they were written on separate command lines
;; = end of a case function in a case statement. (see `case` further down)
$ = prefix to a variable like “$myvar”
$! = PID of the last child process.
$$ = PID of current process (PID == Process ID)
$0 = Shows program that owns the current process.
$1 = First agument supplied after the program/function on execution.
$2 = Second agument supplied after the program/function on execution. ($3 etc.)
$# = Shows the number of arguments.
$? = Any argument (good to use in `if` statements)
$- = current option flags (I never ever had to use this one)
$_ = Last argument/Command
$* = All arguments
$@ = All arguments
# = remmed line, anything on a line after “#” will be overlooked by the script
{ = start braces (starts a function)
} = end braces   (ends a function)
[ = start bracket (multiple-argument specifiers)
] = end bracket (multiple-argument specifiers)
@ = $@ is equivalent to “$1” “$2″ etc. (all arguments)
* = wild card (* can substitute any number of characters)
? = wild card (? can substitute any single character)
” = quote
‘ = precise quote. (Will even include “‘s in the quote)
` = command quote. (variable=`ls -la` doing $variable will show the dir list)
. = dot will read and execute commands from a file, ( . .bashrc )
& = and. as suffix to executed file makes it go to the background(./program &)
0> = stdin stream director (I never seen this used in any script)
1> = stdout stream director (standard output)
2> = stderr stream director (standard error output)
% = job character, %1 = fg job 1, %2 = fg job 2, etc.
>> = stream director append to a file
<< = stdin stream director. (cat > file << EOF ; anything ; EOF)
> = stream director that will start at the top of the file
    (in if statements < and > may be used as greater-then
    and lesser-then, as: if [ “$1” >= “2” ])
\ = back-slash, takes away any special meaning with a character,
     \$var will not be treated as a variable.
     (and a new line will not be treated as a new line)
     Also a \ before a command, removes any alias on the command as: \rm
>& = stream director to stream director, ie. echo “a” 1>/dev/null 2>&1
     this directs 2> to the same place as 1>

——————————————————————————-

Here is the basic UNIX or rather Linux directory structur:

The /usr directory contains a whole lot of things, mainly user accesseble
things, like binarys in /usr/local/bin/ and /usr/bin/ also librarys
in /usr/lib/ and /usr/local/lib/.
The kenrel source should also be under /usr, in /usr/src/linux/
But more about that later.

——————————————————————————-

Here’s an example of the following files locations:

/dev/null
/dev/fd0
/etc/passwd
/home/alien/.profile
/usr/local/bin/BitchX

——————————————————————————-

And a final example that’s a bit more stripped, just incase you are really
new to computers.
Here following files locations:

/dev/null
/dev/audio
/dev/hda1
/etc/passwd
/etc/shadow
/home/alien/.profile
/home/alien/tmp/somefile
/home/user/.bash_profile
/usr/local/bin/BitchX
/sbin/shutdown

——————————————————————————-

This is the same structure as on any Operating System that uses directorys,
Though some Operating Systems may call the / directory C: and some other
may call it HD etc.
and ofcorse some of the directory names in Linux/UNIX are UNIX specific.

No further explanation should be nessesary.

After reading this tutorial, brows around the system and try to learn
what all the files does, just dont remove any files you didnt put there
until your ABSOLUTLEY sure of what you are doing.

——————————————————————————-

Here’s a few UNIX commands just for illustration:

echo
======
echo will *echo* anything you add to it like this:

alien:~$ echo “blah”
blah
alien:~$

To get it to echo without a new line add the suffix -n
like this:

alien:~$ echo -n “blah ”
blah alien:~$

I’ll get back to why you want to do “-n” sometimes in a while.

read
======
read will read from the keyboard (stdin) and save it as a variable
the variable name goes after the read command, like this:

alien:~$ read myvar
<here I type say “blah”>
alien:~$ echo $myvar
blah
alien:~$

To combine these two commands (echo and read) in a small script
line, it can look like this:

alien:~$ echo -n “password: ” ; read pass ; echo “Your pass is $pass”
password: <here I type “mypass”>
Your pass is mypass
alien:~$

Get the basic idea ?

——————————————————————————-

Anyway, here are some commands that you should know before moving on with this
tutorial –
[*] after == important to know.
[X] after == very basics will do.

ls [*] Ex: ls -la Long directory listing.
echo [*] Ex: echo “foo” Does what it says.
cat [*] Ex: cat /etc/passwd Dump out the content of a file.
less [X] Ex: less /etc/passwd Scroll up and down in a file (q = exit)
head [X] Ex: head -5 /etc/passwd Get the 5 (-5) first lines of a file.
tail [X] Ex: tail -7 /etc/passwd Get the 7 (-7) last lines of a file.
grep [*] Ex: grep x /etc/issue Dump lines containing x from /etc/issue
chmod [*] Ex: chmod a+x file Give everyone executable rights to file
chown [X] Ex: chown root file Change owner of file to root.

(cd [-] Ex: cd /etc Change Directory to /etc)

Some applications you need to know how to operate (basics will do) :

any text editor (preferably emacs or vi – they are explaind last in this file)
telnet Ex: telnet 127.0.0.1 Opens a connection to IP 127.0.0.1
lynx Ex: lynx http://foo.bar A command line based web browser.
ftp (ncftp) Ex: ncftp ftp://foo.bar A command line based ftp client.
ssh Ex: ssh 127.0.0.1 Opens a secure connection to 127.0.0.1

These are all explained fully later in this tutorial.

——————————————————————————-

Now don’t sit there and ask yourself how’s going to teach you the commands
or applications I just listed here above. use the manual pages.
like this:

man echo

that will get you the full manual on the command echo 🙂
man works the same way with applications that you have the manual pages for.

To get out of the manual page just press the letter “q”.
“q” quits it and bet’s you back to the command line prompt.
man uses all the normal “less” commands.

Or read further down in this tutorial in the basic Linux/UNIX commands and
operations section (8).

——————————————————————————-

The key to shell scripting just as with any programming language/Operating
System is to REALLY understand what you are doing, so do read this file
more then once, and don’t read it to fast.
Take your time and let it sink in, so you know what it’s all about,
and do take time to read manual pages and do some playing with the commands
so you learn them.

Now that should be enough of what you *should* know before starting to learn
UNIX shell scripting.

So here we go…….

===============================================================================
2 – Where to start
===============================================================================

You should always start with very simple scripts that you really don’t have
any practical use for but still *could* be of practical use =)

As for first let’s make what we already know to a *real* executable script.
Open a text editor (name the file myscript.sh) and type this:

#!/bin/bash

echo -n “password: ”
read pass
echo “Your pass is $pass”

save & exit — then do this command: chmod u+x myscript.sh
Then we can execute it:

alien:~$ ./myscript.sh
password: <type what you want>
Your pass is <what you typed>
alien:~$

The “#!/bin/bash” at the start of the file is to let the script know what
shell type it should use.

The “chmod u+x myscript.sh” is to make it executable.
(change-mode user+execute-right-on myscript.sh) ….. read the manual pages
on chmod for more info on it =)

——————————————————————————-

Take alot of time to play around in your system, open files, figure out
what they do (but don’t edit or remove them).

Take time also to learn some good text editor, that’s important.
Learn, emacs or vi, those are by most people considerd the absolutly best,
but jed, joe, elvis, pico or any simple editor like that will do
just fine for now.

emacs and vi are explained later in this tutorial.

——————————————————————————-

Another thing before moving on is that you can export a variable from a
script.

Say that you have the variable “$var” in a script and want to export
it to the system for use with some other script or something, you can
do: export var

Like this little script:

——————————————————————————-

#!/bin/bash

VAR=”10″
export VAR

——————————————————————————-

Note: VAR=”10″ can not be written as VAR = “10”, since it’s
‘whitespace-sensetive’.

——————————————————————————-

But more to how to make scripts in a second, I just thought that this would
be a good time to enlighten you about this.

So here we go ….

===============================================================================
3 – Beginning techniques.
===============================================================================

First off I’m going to show how to count in bash or how to use your command
line as a calculator, which is really easy and useful.

alien:~$ echo $[ 4 * 2 ]
8
alien:~$

or another example:

alien:~$ echo $[ 10 + 5 ]
15
alien:~$

Easy ? …. I think it is =)

The internal calculator can also be used like this:

alien:~$ echo $(( 10 + 5 ))
15
alien:~$

The second way of using the internal shell calculator is here just
so you dont get confused if you see it used that way sometime.

——————————————————————————-

Now I’d like to show the *string comparing* with “if” statements,
which can be a little hard at first contact, but as soon as you get
familiar with it, it wont be any problems.
So here’s an example.

——————————————————————————-

#!/bin/bash

echo -n “enter a name: ”
read var1
echo -n “enter another name: ”
read var2

if [ “$var1” = “$var2” ]; then
echo “The names are the same”
else
echo “The names were not the same”
fi

exit 0

——————————————————————————-

Note: “fi” is the ending of if, just like a “}” is the ending of a “{“,
exit 0 terminates the script correctly and returns you to the prompt.

Another note is that instead of ‘=’ you can use ‘-eq’ to test if
2 expressions are equal, or ‘-eg’ to check if 2 integers are equal, etc.

       It should also be said that a variable say ‘$var’ can be written
       as this: ${var}, just so you know if you see it done that way
       in some scripts, but here we will use the $var way.

——————————————————————————-

This example if executed looks like this:

(Matching names)

alien:~$ ./script1.sh
enter a name: smurf
enter another name: smurf
The names are the same
alien:~$

(Non-matching names)

alien:~$ ./script1.sh
enter a name: smurf
enter another name: guru
The names were not the same
alien:~$

You can compare any 2 strings with this, as this *mid script example*:

…
if [ “$user” = “gnu” ]; then
echo “Hello user gnu !”
else
echo “I don’t know you.”
fi
…

This compares a variable with a static string which you can set to anything.
You can also do this the other way around.

…
if [ “$user” != “gnu” ]; then
echo “I don’t know you.”
else
echo “Hello user gnu !”
fi
…

The ‘!=’ means NOT-IS, in clear text if the 2 strings are not a match.
As the above example in straight English:

…
if the variable don’t match the word gnu, then
say “I don’t know you.”
in other cases
say “Hello user gnu !”
…

If you think that a variable may not contain anything and you wanna avoid
it showing you errors you can add an x as the first character to both
the statements to test with if, like this to compare $one with -x:

…
if [ “x$one” = “x-x” ]; then
echo “$one is -x”
else
echo “$one is not -x”
fi
…

In plain english:

…
if (contents of $one) equals -x (supress error messages if any), then
say (contents of $one) is -x
in other cases
say (contents of $one) is not -x
…

This previous way is actually quite old, and only a precaution, say this:

…
echo -n “enter a number: ”
read foo
if [ $foo = 2 ]; then
echo ok foo
fi
…

Now, if you with this example dont enter any number there will be nothing
there for if to compare with, not even a blank “”, since we’re not
using quotes, but as this:

…
echo -n “enter a number: ”
read foo
if [ x$foo = x2 ]; then
echo ok foo
fi
…

There will always be something, because if $foo is nothing there is
still x.
Just read acouple of times and you’ll get it.

You can also test if a variable contains anyting at all like this:

…
echo -n “enter a number: ”
read foo
[ -n $foo ] &&
echo ok foo
…

This uses the same options as the test command, so “-z” will return true
if the variable is empty, “-z” will return true if the variable is not
empty etc, it’s ok if you dont understand this right now ….
I’ve added this for the second time readers.

You can also test if a command turns out as true, like this:

…
if echo “foo” >/dev/null; then
echo “foo”
else
echo “bar”
fi
…

Here if will check if foo echos to /dev/null, and if so, then it will
print out “foo” and if foo didnt echo to /dev/null, it’ll print out
the word “bar”

Anoter and perhaps *cleaner* way of doing the same is this:

…
if (echo “foo” >/dev/null); then
echo “foo”
else
echo “bar”
fi
…

It’s the exact same thing but with parenthases around the command,
it looks much cleaner … and so the code is easyer to follow.

You can also make if think ‘if this is a match or that is a match’, like
if the variable is one of two options do one thing else do another.
Like this:

…
if [ “$user” = “gnu” -o “$user” = “ung” ]; then
echo “Hello $user !”
else
echo “I never heard of $user…”
fi
…

The ‘-o’ means OR in an if statement, so here is the example in plain english:

…
if the variable matches the word gnu or matches the word ung, then
say Hello word ! (the word is the variable, now gnu or ung)
in other cases
say “I never heard of word… (the word is whatever the variable is set to)
…

——————————————————————————-

Note: The quotes are needed in an if statement in case the strings or
      variables it’s suppse to compare is empty, since
      if [ foo = ]; then
      would produse a syntax error, but
      if [ “foo” = “” ]; then
      would not.

——————————————————————————-

The ‘-o’ can also be made with ‘] || [‘, so that:
if [ “$user” = “gnu” -o “$user” = “ung” ]; then
can also be expressed as this:
if [ “$user” = “gnu” ] || [ “$user” = “ung” ]; then
You dont really need to remember that, but for the knowlidge I desided
to make a note out of that anyway, mostly for the more experianced readers
of this tutuorial, and for the readers that have read it several times.

——————————————————————————-

You can also set static text in a variable, which is really easy:

——————————————————————————-

#!/bin/bash

anyvar=”hello world”

echo “$anyvar”

exit 0
——————————————————————————-

Which executed would look like this:

alien:~$ ./myscript
hello world
alien:~$

Easy enough ? =)

——————————————————————————-

Now let’s move on to “for” and common for-loops.
I am actually only going to show one sort of for-loop example, of the reason that
at this stage no more is needed, and would only confuse.
as a note, for loops-can be uses (as soon shown) to import strings
from a file to be used as variables in the script.

Now, here’s the example:

——————————————————————————-

#!/bin/bash

for VAR in `cat list.txt`; do
echo “$VAR was found in list.txt”
done

exit 0

——————————————————————————-

Note: “done” terminates the loop when finished.
“in” and “do” are like bash *grammar*, I’ll explain that later.

      The `cat list.txt` part, the `s around the command will make sure
      the script/line executes that part as a command, another way of
      doing this is to: $(cat list.txt)
      which has the same effect.
      That’s just a note so you wont get confused if you see it used
      that way some time.

——————————————————————————-

The previous script example is dependent on that there is a file called
“list.txt”, so let’s make such, and fill it with something like this:

list.txt

123
234
345
456
567
678
789
890

——————————————————————————-

Then the executed script would look like this:

alien:~$ ./script2.sh
123 was found in list.txt
234 was found in list.txt
345 was found in list.txt
456 was found in list.txt
567 was found in list.txt
678 was found in list.txt
789 was found in list.txt
890 was found in list.txt
alien:~$

——————————————————————————-

Note: A space in a file read by a for-loop is taken the same way as a new line.

——————————————————————————-

Here is another example, with a for-loop with an if statement:

——————————————————————————-

#!/bin/bash

for VAR3 in `cat list.txt`; do
if [ “$VAR3” = “789” ]; then
echo
echo “Match was found ($VAR)”
echo
fi
done

exit 0

——————————————————————————-

And executed that looks like this:

alien:~$ ./script3.sh

Match was found (789)

alien:~$

If you have read this in a calm fashion it should be quite clear to you
so far, but before I move on to real practice examples I will explain
the while-loop, and some, more which can be used as to count and more,
for various purposes, as you will see.
You don’t have to *understand* all of how this works, but you should
at least learn it.

So here we go on an example with “while”:

——————————————————————————-

#!/bin/bash

count=”0″
max=”10″

while [ $count != $max ]; do count=`expr $count + 1`
echo “We are now at number: $count”
done

exit 0

——————————————————————————-

Note: expr is a calculator command, you can read more about it later in
this tutorial.

——————————————————————————-

This in plain English reads the following:

make variable “count” hold the number 0
make variable “max” hold the number 10

while 0 is not 10, do add 1 to 0 (each loop until it is 10)
say “We are now at number: $count” (each time 1 is added as long as we are
in the loop)
end the loop
return to the prompt command line.

——————————————————————————-

Which executed looks like, (you guessed it), this:

alien:~$ ./count.sh
We are now at number: 1
We are now at number: 2
We are now at number: 3
We are now at number: 4
We are now at number: 5
We are now at number: 6
We are now at number: 7
We are now at number: 8
We are now at number: 9
We are now at number: 10
alien:~$

——————————————————————————-

Here is another example of a while loop.

#!/bin/bash

agreement=
while [ x$agreement = x ]; do
    echo
    echo -n “Do you agree with this ? [yes or no]: ”
    read yesnoanswer
    case $yesnoanswer in
        y* | Y*)
          agreement=1
;;
        n* | n*)
      echo “If you don’t agree, you can’t install this sofware”;
      echo
      exit 1
;;
    esac
done

echo “agreed”
echo
——————————————————————————-

This in plain English reads the following:

Make an unknown variable named agreement
while the unknown variable is unknown and doesnt match the case,
say “Do you agree with this ? [yes or no]: ”
read the the answer into the “yesnoanswer” variable.
make a case and check the “yesnoanswer” variable for any words beginning
with y or Y, and if so, skip the rest and go on with the script
and say “agreed”.
if it doesnt begin with y or Y, check if it starts with n or N.
If it does start with a n or N, then say:
“If you don’t agree, you can’t install this sofware”
and quit the script.

——————————————————————————-

Which executed looks like this:

alien:~$ ./agree.sh

Do you agree with this ? [yes or no]: something

Do you agree with this ? [yes or no]: yes
agreed

Again executed, but with ‘no’ as answer:

alien:~$ ./agree.sh

Do you agree with this ? [yes or no]: nothing
If you don’t agree, you can’t install this sofware

alien:~$

——————————————————————————-

Note that “nothing” begins with ‘n’ and therfor matches what the script is
looking for, y or Y, and n or N.

Also see later in the tutorial about `case` statements.

——————————————————————————-

Now I’m going to explain shortly about functions in bash.

A function is like a script within the script, or you could say that
you make your own little command that can be used in a script.
It’s not as hard as it sounds though.

So here we go on a example:

——————————————————————————-

#!/bin/bash

function myfunk {
echo
echo “hello”
echo “this is my function”
echo “which I will display twice”
}

myfunk
myfunk

exit 0

——————————————————————————-

Which executed looks like this:

alien:~$ ./funk.sh

hello
this is my function
which I will display twice

hello
this is my function
which I will display twice
alien:~$

——————————————————————————-

Another example of functions can look like this:

——————————————————————————-

#!/bin/bash

myvar=”$1″
var2=”$2″

if [ “$myvar” = “” ]; then
echo “Usage: $0 <integer> <integer>”
exit 0
fi

function myfunk {
expr $1 + $2
}

myfunk $myvar $var2

exit 0

——————————————————————————-

Which executed looks like this:

Without any arguments:

alien:~$ ./funk.sh
Usage: ./funk.sh <integer> <integer>

With arguments:

alien:~$ ./funk.sh 12 3
15
alien:~$

——————————————————————————

Note: the $1 and $2 in the function is infact the first and second argument
      supplied after the function name when it’s called for within the script,
      so you could say that a function is like a separate scrip in
      the main script.

——————————————————————————

Yet another example of a function is this:

——————————————————————————

#!/bin/bash

myvar=”$1″

if [ “$myvar” = “” ]; then
echo “Usage: $0 <number>”
exit 0
fi

function calcfunc { expr 12 + $1 ; }

myvar2=`calcfunc 5`

echo “welcome”
echo “Now we will calculate 12 + 5 * $myvar”

echo “the answer is `expr $myvar2 ‘*’ $myvar`”

——————————————————————————-

Which executed looks like this:

Without any arguments:

alien:~$ ./funk.sh
Usage: ./funk.sh <number>
alien:~$

And with arguments:

alien:~$ ./funk.sh 23
welcome
Now we will calculate 12 + 5 * 23
the answer is 391
alien:~$

——————————————————————————

And for the sake of knowlidge it should also be said that a function can be
declared in the following ways aswell:

——————————————————————————

#!/bin/bash

function foo() {
echo “hello world”
}

foo

——————————————————————————

#!/bin/bash

foo () {
echo “hello world”
}

foo

——————————————————————————

Note that the paranteses after the funtion name are the new thing here.
It’s used exactly the same way as without the paranteses, I just
added that here so that you wont get confused if you see it made that
way sometime.

——————————————————————————

So if you make a function, to call for it (to make use of it), just use the
the functions name just as if it had been a command.

If there is anything that’s uncertain at this point, go back and read it again,
until you understand it, or at least get the basic idea. =)

===============================================================================
3 – Other techniques.
===============================================================================

Now let’s move on to a little bit more advanced shell scripting.
Actually it’s not that advanced, just more hard to keep in order, but let us
leave that to the head of the beholder….. errr
Anyway, let’s not make this harder then it is, so here we go, with a script
example:

——————————————————————————-
#!/bin/bash

> file1.c

cat >> file1.c << EOF
#include <stdio.h>
int main ( void )
{
printf(“Hello world\n”);
return 0;
}
EOF

cc file1.c -o file1 || gcc -o file1 file1.c
./file1

rm -f file1.c file1

exit 0

——————————————————————————-

And here as follows, is an semi-english translation of the script:

echo nothing to file1.c to create it.

cat to file1.c what comes here after in between the “EOF”‘s
// — a short hello world program in C code — //

try if there is a ‘cc’, if not then use ‘gcc’
Execute the newly compiled file

remove file1.c and file1

exit the script.

——————————————————————————-

This can be very useful, since bash do have it’s limitations, so if you
ever need something more powerful or just something else, you can always
do like the script told.

Another little trick with the same thing in a script is:

more << EOF
Here you can type whatever,
like an agreement text or something.
EOF

Play around with it.

——————————————————————————-

Here let’s have a look at the “case” command, case is like “if” ended
with it self backwards.
So that what starts with “case” ends with “esac”, here’s an example of “case”:

——————————————————————————-

#!/bin/bash

case “$1” in
    foo)
    echo “foo was written”
    ;;
    bar)
    echo “bar was written”
    ;;
    something-else)
    echo “something-else was written”
    ;;
esac

——————————————————————————-

This is the same as saying:

….
if [ “$1” = “foo” ];then
echo “foo written”
fi
if [ “$1” = “bar” ];then
echo “bar was written”
fi

etc.
….

so case is far shorter if you have alot of arguments.

Here’s a better example:

——————————————————————————-
#!/bin/bash

case “$1” in
    –help)
    echo “Usage: $0 [–help] [–port <port>] <host> [–time]”
    ;;
    –port)
    telnet $3 $2
    ;;
    –time)
    date
    ;;
esac

——————————————————————————-

This is not very hard to learn,
case the first argument vector ($1) in
firt-possible-match)
if it matches do ……..
close the ) with ;;
etc. down to “esac”

Really not much more to say about the case command at this point.

——————————————————————————-

Now let’s have a REALLY quick look at the command `sed`, which is used
to format text. say now that you have a file called “tmp” that
contains the following:

http://www.metacrawler.com
http://www.yahoo.com
http://www.webcrawler.com

and you want to change all the “www”‘s to “ftp”, then you do like this:

sed ‘s/www/ftp/g’ tmp

and if you want to store the changes to a file you can do:

sed ‘s/www/ftp/g’ tmp > tmp2

This is not sed’s only use, but for sure it’s what it’s most used for.

Here’s just one other really simple thing sed could be used as:

sed -n 3 p /etc/passwd

This will print out the 3’d line of the /etc/passwd file.

——————————————————————————-

Now let’s take up a really interesting command `dialog`, that is a command
with which you can create ncurses dialog boxes.
Ncurses dialog boxes are what one would call ‘console graphics’ or
‘ascii color graphics’, if you ever seen a blue background and a gray box
asking questions, with an <OK> and <Cancel> button, while running
something in a console you have seen an ncurses dialog box.

Now here is a small script example of a dialog box:

——————————————————————————-

#!/bin/bash

dialog –backtitle “My first dialog” \
       –title “Main menu” \
       –menu “Make your choice” 13 60 6 \
        1 “First option” \
        2 “Second option” \
        3 “Exit” 2> .tempfile
        output=`cat .tempfile`
        rm -f .tempfile

if [ “$output” = “1” ]; then
dialog –msgbox “First option was entered” 5 40
fi

if [ “$output” = “2” ]; then
dialog –msgbox “Second option was entered” 5 40
fi

exit 0

——————————————————————————-

Here is another very small example with dialog boxes:

——————————————————————————-

#!/bin/bash

dialog –yesno “Do you agree, jada jada” 10 50 && \
dialog –yesno “ok you agreed” 10 50 || \
dialog –yesno “ok fine, leav then …” 10 50

——————————————————————————-

If the first one (Do you agree, jada jada) returns ‘true’ (yes)
then it walks on to the next (ok you agreed),
and if any of those first two returns ‘false’ (no) it will display
the last (ok fine, leav then …).

——————————————————————————-

Notes: The back slashes “\” are used to say “no new line” as in what comes
       on the next line will be treated as if it were on the same line as
       the last line, the “\” really means that the next character’s
       (in this case the new lines) special meaning is overlocked.

       Just in case you didnt understand, the numbers after, like 10 50:
       dialog –yesno “ok fine, leav then …” 10 50
       is the geometry of the window.
       First number is height and the second width.

       Another note being that the command `Xdialog` works the same as
       dialog, but I wont take that up here because it doesn’t come as default
       with any other Linux distribution then Mandrake, as far as I know.

       A final note is that the `dialog` command is getting to be out dated
       but is still the most used, the newer version of it is named `whiptail`
       and works the same as `dialog`, but looks slightly different.

——————————————————————————-

Now we have covered most of it, so let’s take up some small tricks, that bash
allows you to do, here follows what it does, and then the code example:

Here we wanna check if you have a directory called “/usr/local/bin”:

if [ -d /usr/local/bin ]; then
cp file /usr/local/bin/
else
echo “NO !!”
fi

Another way of doing the same thing is this:

test -d /usr/local/bin && cp file /usr/local/bin/ || echo “NO !!”

Or:

ls /usr/local/bin/ && cp file /usr/local/bin/ || echo “NO !!”

The last way is a bit messy, but alot smaller then the first one,
but here’s yet another way that’s small and less messy:

ls /usr/local/bin/ 1>/dev/null 2>&1 && cp file /usr/local/bin/ || echo “NO !!”

That might look really weird at first sight, but it’s easy if you break it
down and look at it:

ls /usr/local/bin/ <<==== lists /usr/local/bin/
1>/dev/null        <<==== sends the contents of the listing to ‘the black hole’
2>&1               <<==== sends any errors the same way… to ‘the black hole’
     (same thing as to say 2>/dev/null)
&&                 <<==== if the first command worked, we will go on here.
cp file /usr/local/bin/   <<==== copy file to /usr/local/bin/
||                 <<==== if the first command didn’t work…
     we go on here instead.
echo “NO !!”       <<==== what it says … say NO !!

as this:
If `ls` can list /usr/local/bin/ next command can be executed, OR if not
it will echo “NO !!”, and all listings/errors are being sent to /dev/null
the ‘black hole’ of a UNIX/Linux.

——————————————————————————-

To prevent that a script is being executed more the once at the same time
for some reason you may wanna let the script make a ‘lock’ file.
This is very easy to do:

#!/bin/bash
ls script.lock 1>/dev/null 2>&1 && exit 0 && echo “lockfile detected”
> script.lock
echo “Here is where the script should be”
rm -f script.lock
exit 0

Here we first check if there is a lockfile, and if there is we terminate
the script and say that a lockfile was detected.
If there is no lockfile, we create one and start to execute the rest of the
script.
At the end of the script we remove the lockfile, so that the script can
be executed again.
All this is just to prevent the same script to be run twice at the same time,
which can be a good thing if your script does something that cant be done
twice at the same time, as mounting a hard drive/cd-rom, using sound or
anything like that.

Another neat little trick is if you from within a script are going to
create temporary files that you want unique (to not overwrite some other
files anywhere, wherever the script may get executed) you can do like this:

#!/bin/bash
echo “ls” >.tmp.$$
echo “-la” >.tmp2.$$
one=`cat .tmp.$$`
two=`cat .tmp2.$$`
$one $two
rm -f .tmp.$$ .tmp2.$$

This will make a file called .tmp.<pid of script> containing the word “ls”,
then it will make a file called .tmp2.<pid of script> containing “-la”.
After that it make 2 variables, each one when being called will `cat` one
of the .tmp.* files each.
At the end we have “$one $two” that will work the same as if we had printed:

ls -la

And last we remove the temporary files.

This is useful if your doing a script that requires you to move around alot
of text from one file to another and back, as this example:

#!/bin/bash

sed ‘s/www/ftp/g’ tmp > .tmp.$$
sed ‘s/com/org/g’ .tmp.$$ > .tmp2.$$
sed ‘s/ /_/g’ .tmp2.$$ > .tmp3.$$
mv -f .tmp3.$$ tmp
rm -f .tmp.$$ .tmp2.$$ .tmp3.$$

exit 0

Here we change all www’s in a file (tmp) to ftp, then we change all com’s
to org, and then all spaces to underscores.
After that we move the fully changed file so it overwrites the original file.
Then removing the temporary files and exit the script.

If you have a good look at it, it’s really easy.

Another nice trick is as I showed in the example prior to the last one:

…
one=`cat .tmp.$$`
two=`cat .tmp2.$$`
…

That a variable can hold a command can prove to be useful, like this:

#!/bin/bash
time=`date +%H:%M:%S`

echo “$time” >> log
echo “some input to the log” >> log
sleep 60
echo “$time” >> log
echo “some input to the log a minute later” >> log

exit 0

But, it can hold more then just a command, it can actually *hold* the contents
of a whole file.
Say now that you made a script and have a pretty large readme file, and want
to display that as a ‘man page’ to the script if the argument `–help`
is used to execute the script, then you can do like this:

#!/bin/bash
one=”$1″
help=`cat README`

if [ “$one” = “–help” ]; then
$help | more
…

Ofcorce it would be easier to say:

#!/bin/bash
if [ “$?” = “–help” ]; then
more README
fi

But these examples are just here for illustration so you get the point
of usage for commands and so.

Another trick is, if you wanna hide script/program you can rename it to:
-bash, that way it will look as a normal bash running in the `ps`
(process list), you rename it by doing:

mv script ./-bash

Then execute it like normal ./-bash

Yet another trick, is if you’re doing a script where you want each line
of a file as a variable, unlike for that takes each word as a variable.
This can be done like this:

#!/bin/bash
file=”$1″
min=”0″
max=`cat $file | wc -l`

if [ “$1” = “” ]; then
echo “Usage: $0 <file>”
exit -1
fi

while [ “$min” != “$max” ]; do min=`expr $min + 1`
curline=`head -$min $file | tail -1`
echo $curline
test $min -eq $max && exit 0
done

The `test` is there to make sure that it will end when $min and $max are the
same.
Now this can be done with `for` if you change IFS (described later), but that
is not recomended, especially if you export IFS since that would change the
enviorment and hence screw with the system scripts if they were to be runned
before changing IFS back to normal, but enough about that now, just keep
it somewhere far back in your head, dont change IFS unless you know what
you’re doing.

If you dont understand this little script at this point, dont worry, you
will understand it the second time you read this tutorial =)

——————————————————————————-

Now let’s take a quick look at arrays in shell scripting.
First off, an array is what it says, it’s an array of something,
now, to declare a variable that can hold an array we create it with the
command `declare`, let’s make a short example:

alien:~$ declare -a foo=(1 2 3 4 5)
alien:~$ echo ${foo[0]}
1
alien:~$ echo ${foo[1]}
2
alien:~$ foo[1]=bar
alien:~$ echo ${foo[1]}
bar
alien:~$

First of all, to understand the declare command better do `help declare`
at a console and it’ll desplay this:

declare: declare [-afFrxi] [-p] name[=value] …
    Declare variables and/or give them attributes. If no NAMEs are
    given, then display the values of variables instead. The -p option
    will display the attributes and values of each NAME.

The flags are:

      -a        to make NAMEs arrays (if supported)
      -f        to select from among function names only
      -F        to display function names without definitions
      -r        to make NAMEs readonly
      -x        to make NAMEs export
      -i        to make NAMEs have the `integer’ attribute set

Variables with the integer attribute have arithmetic evaluation (see
`let’) done when the variable is assigned to.

    When displaying values of variables, -f displays a function’s name
    and definition. The -F option restricts the display to function
    name only.

Using `+’ instead of `-‘ turns off the given attribute instead. When
used in a function, makes NAMEs local, as with the `local’ command.

So here we see that the -a switch to declare makes the variable an array.
So after getting that `declare -a` we declare the variable as an array,
with the array within paranteses.

And then to make use of it, we use the way to write a variable like this:
${ variable name here }
and the number inside the []’s is the number that points to which part of
the array it should use, begining from 0 which is the first.

Let’s make another short example:
declare -a foo=(this is another example)
echo “The array (${foo[*]}) has (${foo[0]}) as first, and (${foo[3]}) as last.”

The output of this would be:
The array (this is another example) has (this) as first, and (example) as last.

Now, this isn’t something you’ll use in every day scripting, but it’s still
something you should know the existance of, just in case you see it or need
it at some point.

——————————————————————————-

Now here’s a less common way of using bash, CGI scripts.
Most people dont assosiate shell scripting with cgi, but it works
just as well as any other language, so here I’d like to to show
you how to make CGI scripts in bash.

——————————————————————————-

Here is the first example which is a simple cgi counter in bash.
A note is that all CGI scripts should be in the servers cgi-bin directory
or any subdirectory there off, unless the server is configured to see
any other directorys as cgi directorys.

——————————————————————————-

#!/bin/bash

test -f date.txt || echo `date “+%B %d %Y”` > date.txt
test -f counter.txt || echo ‘0’ > counter.txt
current=`cat counter.txt`
date=`cat date.txt`
visitor=`expr $current + 1`

echo “$visitor” > counter.txt
echo ‘Content-type: text/html’
echo ”
echo ‘<br>Vitor:’
echo ‘<br>’$visitor'<br>Since’
echo ‘<br>’$date'</br>’

——————————————————————————-

Let’s take this one line by line here:

First the shell ….
#!/bin/bash

Then we test if there is a file called date.txt, if not then we echo the
current date to it and hence creating it.
test -f date.txt || echo `date “+%B %d %Y”` > date.txt

Then we test if there is a file called counter.txt and if not we echo a 0
to it and so create that one too.
test -f counter.txt || echo ‘0’ > counter.txt

Now we declare the variables, current is the contents of counter.txt.
current=`cat counter.txt`

The date variable is the contents of date.txt.
date=`cat date.txt`

And visitor is the sum of the contents of counter.txt + 1.
visitor=`expr $current + 1`

And then we echo the new increased number to counter.txt.
echo “$visitor” > counter.txt

And here comes the HTML part. the first to line is the ‘cgi header’
those should ALWAYS be there:
echo ‘Content-type: text/html’
echo ”

Then we move on to the *real* html:
echo ‘<br>Vitor:’
echo ‘<br>’$visitor'<br>Since’
echo ‘<br>’$date'</br>’

The <br> is a linebreak in html
The bash variables have to be *ouside* the ‘s else they will simply show
up as $visitor or $date litterly, that’s why it’s made like this:
echo ‘text’ $variable ‘some more text’
So that the text is enclosed with ‘s, but the variables are between or rather
outside of them.
Anyway, this cgi will create a section that looks like this on a webpage:

—————-
   Vitor:
     1
   Since
May 29 2001
—————-

To add that to a html code you add this tag to your html/shtml page:
<!–#exec cgi=”<path to counter>” –>

With the path to the counter it could look like this:

<!–#exec cgi=”/cgi-bin/counter/counter.cgi” –>

Not so hard is it ?

——————————————————————————-

Here is another example of a CGI script in bash (actually the second CGI
script I ever made).

——————————————————————————-

#!/bin/bash

method=`echo $QUERY_STRING | awk -F’=’ ‘{print $1}’`
host=`echo $QUERY_STRING | awk -F’=’ ‘{print $2}’`

if [ “$method” = “nslookup” ]; then
echo ‘Content-type: text/html’
echo ”
echo ‘<html>’
echo ‘<body bgcolor=”white”>’
echo ‘<center>’
echo ‘<br>nslookup ‘$host’ (This might take a second)<br>’
echo ‘<hr width=”100%”>’
echo ‘</center>’
echo ‘<pre>’
nslookup $host
echo ‘</pre>’
echo ‘<center>’
echo ‘<hr width=”100%”>’
echo ‘<br>nslookup compleat’
echo ‘</center>’
echo ‘</body>’
echo ‘</html>’
fi

if [ “$method” = “ping” ]; then
echo ‘Content-type: text/html’
echo ”
echo ‘<html>’
echo ‘<body bgcolor=”white”>’
echo ‘<center>’
echo ‘<br>ping ‘$host’ (This might take a second)<br>’
echo ‘<hr width=”100%”>’
echo ‘</center>’
echo ‘<pre>’
ping -c 5 $host
echo ‘</pre>’
echo ‘<center>’
echo ‘<hr width=”100%”>’
echo ‘<br>ping compleat’
echo ‘</center>’
echo ‘</body>’
echo ‘</html>’
fi

if [ “$method” = “scan” ]; then
echo ‘Content-type: text/html’
echo ”
echo ‘<html>’
echo ‘<body bgcolor=”white”>’
echo ‘<center>’
echo ‘<br>Scanning host ‘$host’ (This might take a minute)<br>’
echo ‘<hr width=”100%”>’
echo ‘</center>’
echo ‘<pre>’
nmap $host
echo ‘</pre>’
echo ‘<center>’
echo ‘<hr width=”100%”>’
echo ‘<br>Scan compleat’
echo ‘</center>’
echo ‘</body>’
echo ‘</html>’
fi

——————————————————————————-

Now let’s take a look at what that means:

——————————————————————————-

This time it wont be all the lines, but all the new parts:

First the 2 variables:
method=`echo $QUERY_STRING | awk -F’=’ ‘{print $1}’`
host=`echo $QUERY_STRING | awk -F’=’ ‘{print $2}’`

These are made this way because of how the CGI script imports the variables
from a form (I’ll come back to this), the $QUERY_STRING variable is
from the webservers enviorment, and so is one of the httpds env variables.

And what you do with the $QUERY_STRING is depending on how you create
your web form …. but as I said I’ll get back to that.

Now the rest:

if [ “$method” = “nslookup” ]; then

That was pretty obvious …. if the first feild of $QUERY_STRING (separated
by a =, is “nslookup”, then go ahead here:

echo ‘Content-type: text/html’
echo ”

Yes the header ….

echo ‘<html>’
echo ‘<body bgcolor=”white”>’
echo ‘<center>’
echo ‘<br>nslookup ‘$host’ (This might take a second)<br>’
echo ‘<hr width=”100%”>’
echo ‘</center>’
echo ‘<pre>’

Create a HTML page … and then after the <pre> we do the actual center part
of the script:

nslookup $host

Which will resolve the DNS of the host (try the command and see),
And after that we end the html page:

echo ‘</pre>’
echo ‘<center>’
echo ‘<hr width=”100%”>’
echo ‘<br>nslookup compleat’
echo ‘</center>’
echo ‘</body>’
echo ‘</html>’

and then end the if statement:

and then the same for the others, just diffent objects at what they should
do, as this was nslookup, the other sections will mnap (portscan) and ping
the host instead.

Now how would a full HTML page look to make use of this cgi script ?
As we this time need input to get the host or IP to scan/ping/nmap.

Well like this:

——————————————————————————-

<html>
<body bgcolor=”white”>
<center>
<p><font size=”+1″>Enter host or IP</font></p>
<hr width=”100%”>
<br>
<form action=”http://www.yourdomain.com/cgi-bin/scan.cgi” method=”get”>
<input type=”text” name=”scan” value=”” size=”30″>
<input type=”submit” value=”portscan”>
</form>
<p>
<form action=”http://www.yourdomain.com/cgi-bin/scan.cgi” method=”get”>
<input type=”text” name=”nslookup” value=”” size=”30″>
<input type=”submit” value=”nslookup”>
</form>
<p>
<form action=”http://www.yourdomain.com/cgi-bin/scan.cgi” method=”get”>
<input type=”text” name=”ping” value=”” size=”30″>
<input type=”submit” value=”ping -c 5″>
</form>
</center>
</body>
</html>

——————————————————————————-

Now what does all this mean ? ….
Well, I wont turn this into a HTML tutorial, but I’ll explain this so you
can make use of bash for CGI.

Right to the important HTML part here:

Here we create a form, as in an input feild, which will add it’s input
(in a specific way) to the end of the url in action=””.
the method is get since we’re getting the output of the cgi script.
we name this feild scan so we get the output this way:
?scan=<input>
Where the <input> is what you typed in the input box.
And then we make an “ok” button that says “portscan”.
So if you type say 127.0.0.1 and press the portscan button the URL it will
be directed to is this:

http://www.yourdomain.com/cgi-bin/scan.cgi?scan=127.0.0.1

And this “scan=127.0.0.1″ will be the $QUERY_STRING enviormental variable.

And so the script is starting to make sense.

——————————————————————————-

Here’s a REALLY simple cgi script just for the illustration aswell.

——————————————————————————-

#!/bin/bash

string=”Hello World”

echo ‘Content-type: text/html’
echo ”
echo ‘<html>’
echo ‘<br>’$string'</br>’
echo ‘</html>’

——————————————————————————-

And the html to call that ….. just a normal hyper link.

And that’s it.

——————————————————————————-

That’s it on the tricks, now let’s move on to practical examples so you get
a little bit of feel for how you can use bash to make things easier for you.

===============================================================================
5 – Practical Scripting Examples.
===============================================================================

I’d first like to add a note which you already probably knows:
./ == look in current directory instead of the “PATH”.
To give that an example, say now that you have a script in your home
directory called “ls” or “dir”, how would you execute that without
getting the contents of the directory ?
well, that’s why you use “./” before a name to execute it if it’s in the
current directory.
../ == previous directory (one directory further up towards “/” then you are
currently in), this can be used as this, say that you have a script called
“script” in “/home/user/” and you are standing in “/home/user/nice/” and
you don’t want to leave the directory but still want to execute the script.
Then you do, “../script” and if you are in “/home/user/nice/blah/” you
you would do, “../../script” —– “../../” == 2 directory’s back.
Get the idea ?

Anyway, now to the practical examples, which are working scripts for
various purposes, to give an idea about what you can do with shell scripting.
New things previously not explained will show up in this section, but
I will explain them as we go along.

Let’s start with simple examples and move on to harder parts.
As for first I’ll stick to useless scripts =) just for illustration.
Explanation on the scripts follow after them, as usual.
So here we go on that.

——————————————————————————-

#!/bin/bash

one=”$1″
something=”$2″

if [ “$one” = “” ]; then
echo “Usage: $0 [name] <anything goes here>”
exit 0
fi

function first {
clear
echo “this is a test script !”
echo
echo “name followed on $0 was – $one – ”
echo
echo “if you typed anything after the name it was: $something”
echo
}

first

exit 0

——————————————————————————-

Executed without any thing after the script name it looks like this:

alien:~$ ./script
Usage: ./script [name] <anything goes here>
alien:~$

Executed with a name it looks like this:

alien:~$ ./script Jerry
—————————————-
this is a test script !

name followed on ./script was – Jerry –

if you typed anything after the name it was:

alien:~$

Executed with a name and something else it looks like this:

alien:~$ ./script Jerry homer
—————————————
this is a test script !

name followed on ./script was – Jerry –

if you typed anything after the name it was: homer

alien:~$

——————————————————————————-

Notes: $0 == the script name’s variable so you can do a “Usage: <scriptname>”
       whatever the script is named after you made it.
       $1 == the first thing that’s typed after the script in the command line
       $2 == the second thing that’s typed after the script in the command line
       $3, $4 and so on …..

one=”$1″ this puts the contents of “$1” into the variable $one
which can be very useful to avoid errors.

clear == clears the screen

——————————————————————————-

This next example is a script which you really shouldn’t use…
It’s here as an example for a working help script, but *could*
cause harm if not used correctly.
So if you loose anything because of using it, it’s all on you.
and don’t say I didn’t warn you.

——————————————————————————-

#!/bin/bash

if whoami | grep -v root >> /dev/null; then
echo “you have to be root to use this”
exit 1
else

for USER in `cat user.list`; do
if cat /home/$USER/.bash_history | grep passwd >> /dev/null; then
    echo
    echo “user $USER have tried to access the passwd file”
    echo “do you want to remove $USER from your system [y/n] ”
read YN
if [ “$YN” = “y” ]; then
    echo “user $USER is being deleted”
    echo “home dir of user $USER is however intact”
    echo
    remuser $USER
else
    echo “user $USER is not deleted”
    echo
fi
else
    echo “$USER haven’t tried to access the passwd file”
fi
done

rm user.list
    echo
    echo “Script finished”
    echo
exit 0

——————————————————————————-

I will just translate this script into real/clear English:

if (check own user-name) is anything else but root >> send output to a black hole
say, “you have to be root to use this”
terminate program.
in other cases (in this case that can only be if the user is root)

list the contents of the file “/etc/passwd” combined with – cut out the
user names (field 1 separated by “:”) grep everything except lines containing the
following words/names: halt operator root shutdown sync bin ftp daemon
adm lp mail postmaster news uucp man games guest nobody and send it
to the file “user.list”
end “if” statement

for each user in the “user.list” file do the following
if the word “passwd” is present in “/home/$USER/.bash_history” >> output to
the systems black hole
say nothing
say “user $USER haver tried to access the passwd file”
say “do you want to remove $USER from your system [y/n]”
read if the input from the keyboard is a “y” or “n”

if the variable for the answer of the input is “y” then
say “user $USER is being deleted”
say “home dir of user $USER is however intact”
say nothing
removing the user from the system that tried to access the passwd file
in other cases
say “user $USER is not deleted”
say nothing
end “if” statement
in other cases
say $USER haven’t tried to access the passwd file
end “if” statement
exit the for-loop

remove the “user.list” file
say nothing
say “Script finished”
say nothing

exit and return to the shell command line.

——————————————————————————-

Note: grep -v == show everything *except* what comes after the -v

——————————————————————————-

Here is another way of doing the exact same script, just to illustrate that
the same thing can be done in several different ways:

——————————————————————————-

#!/bin/bash

if [ “$UID” != “0” ]; then
echo “you have to be root to use this”
exit -1
fi

for uids in `cat /etc/passwd`; do
    useruid=`echo “$uids” | awk -F’:’ ‘{print $(3)}’`
    test “$useruid” -ge “500” 2>/dev/null &&
    echo “$uids” | awk -F’:’ ‘{print $(1)}’ > user.list
done

for USER in `cat user.list`; do
    if (grep passwd /home/$USER/.bash_history >/dev/null); then
       echo
       echo “user $USER have tried to access the passwd file”
       echo “do you want to remove $USER from your system [y/n] ”
       read YN

       case $YN in
            y* | Y*)
        echo “user $USER is being deleted”
            echo “home dir of user $USER is however intact”
            remuser $USER
        echo
        ;;
            n* | N*)
        echo “user $USER is not deleted”
        echo
        ;;
       esac
    else
       echo “$USER haven’t tried to access the passwd file”
       rm -f user.list
       echo
       echo “Script finished”
       echo
    fi
done

exit 0

——————————————————————————-

Since this script does the exact same thing, but in another way, I’ll leav you
with the experiance of trying to figure out the differences and how it
works with the help of this tutorial, you might not get this right until
you’ve read this tutorial twice.

A tip is: try to make a comment to each line with what it does and why.

——————————————————————————-

This below script is a “Wingate” scanner, to scan for wingates that can
be used to bounce off and such things, don’t know if that’s really legal
so take that on your own risk.

Anyway here comes the script:

——————————————————————————-

#!/bin/bash
echo > .log.tmp
echo > .log2.tmp
echo “sleep 7” > wg.config
echo “killall -2 telnet” >> wg.config

scan=”$1″
count=”0″
max=”255″

clear

if whoami | grep root >> /dev/null ; then
echo “please use this as user and not root, since it would kill all users”
echo “telnet sessions”
else
clear
fi

if [ “$1” = “” ]; then
        echo ” usage is: $0 <C host> ”
        echo ” examples:”
        echo ” $0 127.0.0″
        echo ” That will scan from 127.0.0.0 to 127.0.0.255″
        echo
        echo “be aware though, while it scans it also kills any other telnet”
        echo “sessions you might have ….”
exit 0
fi

while [ “$count” != “$max” ]; do count=`expr $count + 1`
        echo “Attempting connection to $1.$count ”
        echo > .log2.tmp
        ./wg.config &
        telnet $scan.$count >> .log.tmp
        cat .log.tmp | grep -v refused | grep -v closed | grep -v Connected | grep -v Escape | grep -v login >> .log2.tmp
        echo >> .log.tmp
    done
echo “Script Finished, results stored in .log.tmp and .log2.tmp”
exit 0

——————————————————————————-

This time I will not translate the script into clear English and I will
not show how it looks executed, I leave that for you to do =)

——————————————————————————

Now a final practical example of a script, this is a small graphical front end
to the console mp3 player `mpg123` so you got to have that to work
and you need to execute this script in a directly where you have mp3’s ….
Also if you want the X-windows part of it to work you need to get and
install Xdialog, you can get that from www.freshmeat.net …
However if you have Linux Mandrake you should be good anyway, Xdialog
comes as default in Mandrake.
This script should be named `xmpg123`.
So here we go:

——————————————————————————-

#!/bin/bash
dialog –backtitle “xmpg123” \
       –title “Main menu” \
       –menu “Make your choice” 13 60 6 \
        1 “X-windows” \
        2 “Ncurses” \
        3 “Exit” 2> .tempfile
        output=`cat .tempfile`
        echo $output
        rm -f .tempfile

if [ “$output” = “1” ]; then
for songs in `ls -1 *.mp3`; do
echo “$songs mp3-file” >> .tempfile
done
output=`cat .tempfile`
Xdialog –menu 2 2 2 1 $output \
        2> .tempfile
        output=`cat .tempfile`
        mpg123 $output
        rm -f .tempfile
fi

if [ “$output” = “2” ]; then
for songs in `ls -1 *.mp3`; do
echo “$songs mp3-file” >> .tempfile
done
menu=`cat .tempfile`
dialog –menu “Make your choice” 13 70 6 $menu 2> .tempfile
       output=`cat .tempfile`
       mpg123 $output
       rm -f .tempfile
fi

exit 0

——————————————————————————-

A note being that dialog and Xdialog seems to be in early stages, so this
may look sort of buggy if you don’t have the great dialog god at your side…

——————————————————————————-
——————————————————————————-

And don’t forget to “chmod u+x <script name> or chmod a+x <script name>
to make your scripts executable.

===============================================================================
6 – Customize your system and shell.
===============================================================================

This section is dedicated to how you can customize your system in various
ways, this section was never planned to be in this tutorial, but since
I have received so many questions on how to do all this, I might as well
include it in the tutorial.

——————————————————————————-

First of I’m going to explain the local settings, this means the settings
that will only affect a single user and not the whole ‘global’ system.
And the most logical way to start this is (I think) to talk about the shell.

——————————————————————————-

At the very top of this tutorial you will find the various types of shells,
default for most systems is /bin/bash, this is set in the /etc/passwd file
so a normal user can not change that.

What a normal user can do if he wants to use another shell is to start it from
his ~/.bashrc file.
So say now that you feel the urge to run tcsh, then just add the
line /bin/tcsh in your ~/.bashrc, this may be done by doing:
echo “/bin/tcsh” >> ~/.bashrc
personally I prefer the standard bash.

But if you do have root (super user) access to the system, you can change
the shell type correctly in the /etc/passwd file.

here’s a user account with /bin/bash from /etc/passwd

User:x:500:500:my real name:/home/user:/bin/bash

And here the same line changed to /bin/tcsh (tenex C shell)

User:x:500:500:my real name:/home/user:/bin/tcsh

——————————————————————————-

Here are the system variables you can use to change your enviorment,
these can be set and exported from your ~/.bash_profile or /etc/profile
It’s not all of the variables but all the really interesting ones,
so here we go:

BASH= this can also set your shell type, it’s most commonly defaulted
to BASH=/bin/bash

BASH_VERSION= this can change the version reply of bash, on my system
this is defaulted to BASH_VERSION=’2.03.19(1)-release’

ENV= this should point to a file containing your enviorment,
this is by default: ENV=~/.bashrc

HISTFILE= this should point to a file that will contain your shell
‘history’, as in your previously used commands.
this is by default set to: HISTFILE=~/.bash_history

HISTFILESIZE= the max aloowed size of the history file, usually around 1000

HISTSIZE= about the same as HISTFILESIZE

HOME= this should point to your home dir

HOSTNAME= this is your hostname

HOSTTYPE= this should return the same as the `arch` command.

IFS= Internal Feild Separator …. this is a delimeter,
often defaulted to a new line as this:
……
IFS=’
‘
……

INPUTRC= defaulted to INPUTRC=/etc/inputrc

LANG= language variable, default is en for english

LANGUAGE= about the same as LANG, also defaulted to en for english

LINGUAS= defaulted to en_US:en also a language variable.

LS_COLORS= sets colors to the `ls` command. this on my system
is defaulted to this:

……
LS_COLORS=’no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:bd=40;33;01:\
cd=40;33;01:or=01;05;37;41:mi=01;05;37;41:ex=01;32:*.cmd=01;32:*.exe=01;32:\
*.com=01;32:*.btm=01;32:*.bat=01;32:*.tar=01;31:*.tgz=01;31:*.tbz2=01;31:\
*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.lha=01;31:*.zip=01;31:\
*.z=01;31:*.Z=01;31:*.gz=01;31:*.bz2=01;31:*.bz=01;31:*.tz=01;31:*.rpm=01;31:\
*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.xbm=01;35:*.xpm=01;35:\
*.png=01;35:*.tif=01;35:*.tiff=01;35:’
……
So just add what you want here, and colors are the same
as explained about how to set the prompt later down, but
without the [ infront and m on the end.

MAIL= mail file, usually MAIL=/var/spool/mail/<username>

OSTYPE= This can change your OS reply, it’s on a linux defaulted
to: OSTYPE=linux-gnu

PATH= changes your path, this variable is explained in
the explanation of the /etc/profile file

PPID= parent pid …. this is a read-only variable …
so you cant change it.

PS1= the prompt variable, explained later down.

PS2= the *more to come* variable, as if you type an unfinished
command string, it will bring you a new prompt where
you can finish it, this is usually defaulted to: PS2=’> ‘

SHELL= another way to change your shell type …

TERM= terminal type, usually defaulted to: TERM=linux
but can also be like: TERM=vt100
there are more video terminals then 100 though.

UID= your user ID, if your root this will be 0,
this is a readonly variable.

USER= your user name ….

USERNAME= same as $USER

Say that you want to change your shell to /bin/csh and your path to just /bin
(you dont), but just if you would in your: .bash_profile add:

——————————————————————————-

SHELL=/bin/csh
PATH=/bin

export PATH SHELL

——————————————————————————-

Not so hard huh ?

——————————————————————————-

The next thing here is a question that I’ve heard alot, and that is “how do I
change my command prompt ?”.

The command Prompts variable is named PS1 ($PS1)

for a prompt that looks like this:
[alien@localhost alien]$
the contents of the PS1 variable would be this:
[\u@\h \W]\$

All the prompts internal variables starts with a \ (backslash)

useful:

\$ = the prompt ($ for user and # for root)
\d = date
\h = abbreviated hostname (root.host.com would become root)
\H = full hostname
\s = shell type
\t = time
\T = time with seconds
\u = username
\v = shell version (short)
\V = shell version (long)
\w = full path
\W = current directory name

less useful:
\e = erase rest of line …. not very useful
\n = new line … not very useful
\r = whatever comes after \r is displayed before the first character.

A couple of examples would be:

*BSD like.
PS1=”\u: \w> ”

DOS like.
PS1=”C:\w > ”

RedHat like.
PS1=”[\u@\h \W]\$ ”

Init 1 like.
PS1=”\s-\v \$ ”

How do I use colors in the prompt ?

To use colors in the prompt you need to be familiar with the escape sequence
color codings, those are as follows:

reset         = ^[[0m
flashing      = ^[[5m
black         = ^[[0;30m
red           = ^[[0;31m
green         = ^[[0;32m
yellow        = ^[[0;33m
blue          = ^[[0;34m
magenta       = ^[[0;35m
cyan          = ^[[0;36m
white         = ^[[0;37m
highblack     = ^[[1;30m
highred       = ^[[1;31m
highgreen     = ^[[1;32m
highyellow    = ^[[1;33m
highblue      = ^[[1;34m
highmagenta   = ^[[1;35m
highcyan      = ^[[1;36m
highwhite     = ^[[1;37m
bg-white      = ^[[47m
bg-magenta    = ^[[45m
bg-blue       = ^[[44m
bg-red        = ^[[41m
bg-black      = ^[[40m
bg-green      = ^[[42m
bg-yellow     = ^[[43m
bg-cyan       = ^[[46m

Important to know is that the leading `^[` is NOT 2 characters, it’s ONE
control character that that takes up the space of 2 characters, or is
described by 2 characters, if you have a real ^[ and you try to delete the
[ do it it will delete both the [ and the ^ at the same time.

————————————————
Not really sure where to put this note but here,
^[[<number>G
Puts the cursor at column <number>, as this:

echo -n “Starting myprog:” && echo -e “^[[50G OK” || echo -e “^[[50G FAILD”
————————————————

So how do you get a real control character ?

Either you use the very old line editor ‘ed’ and press Ctrl+[ to get the
control character (ed commands are described at the end of this tutorial),
or you can use ’emacs’ or the text editor ‘joe’.

To get control characters in emacs you press ^Q and ^<what you want>,
as if you want a ^[ you press ^Q^3, and then ^X^S^X^C to save and quit.

To get control characters in joe you press ` and then the character to make
a control character, in this case [, when you do this in joe the ^[
should look like a bold [.
To save and quit in joe you press: Ctrl+K followed by Ctrl+X

It’s only the ^[ that is a control character the rest is normal [‘s and
numbers and so on.

Don’t forget to enclose all your colors codes in \[ \], this means that
^[[0;31m (red) would be written as \[^[[0;31m\].

Where do I write this and how does an example look ?

You add this in your ~/.bash_profile, you can put it at the end of the file.

Some examples are:

[ highblue-user red-@ highblue-host green-dir ] highblue-$
PS1=”\[^[[1;34m\u^[[0;31m@^[[1;34m\h ^[[0;32m\W^[[0m\]^[[1;34m\$ \[^[[0m\] ”

highblue-user highwhite-: highblue-path >
PS1=”\[^[[1;34m\]\u\[^[[1;37m\]: \[^[[0;31m\]\w \[^[[0m\]> ”

(you can not cut and paste these examples without editing the ^[‘s to real
control characters, and know that a color prompt is almost always buggy)

——————————————————————————-

The next thing to take up is how to set aliases and to change system variables.

An alias is set in the ~/.bashrc file, if you use /bin/bash else, it’s most
likely in your .`shell type`rc as .zshrc .csh .tcsh etc.

An alias means that you can make a short command for a longer command,
as the alias `l` can mean `ls` and the alias `la` can mean `ls -la`, and
so on, an alias is written like this (also a list of useful aliases):

alias rm=’rm -i’
alias mv=’mv -i’
alias cp=’cp -i’
alias s=’cd ..’
alias d=’ls’
alias p=’cd -‘
alias ll=’ls -laF –color’
alias lsrpm=’rpm -qlp’
alias lstgz=’tar -tzf’
alias lstar=’tar -tf’
alias mktgz=’tar -cfz’
alias untar=’tar -vxf’
alias untgz=’tar -vzxf’

rm will now ask before removing anything.

mv will now ask before overwriting anything.

cp will now ask before overwriting anything.

s will now work as cd ..

d will now work as ls.

p will now work as cd – (cd – == takes you to your last dir ie.
you are in /usr/local/bin/ and does a cd /, if you from here wanna go back
to /usr/local/bin/ you simply type `cd -`, or now just `p`.)

ll will do a ls -la with colors and ending * after executable files and ending
an ending / after dirs.

lsrpm will list the contents (where the files will end up if you install it) of
any rpm file.

lstgz will list the contents of a .tar.gz or .tgz file.

lstar will list the contents of a plain .tar file.

mkgz will make a tgz archive (mktar archive.tgz directory).

untar will untar a .tar file.

untgz will unzip and untar a .tar.gz or a .tgz file.

There is more alias like things you can set in the ~/.bashrc file, like
smaller functions that works as aliases, like this:

function whichrpm { rpm -qf `’which’ $1`; }

typing “whichrpm <command>” at a prompt will name the rpm file it came with.

the rpm -qf command works like this:

alien:~$ rpm -qf /usr/bin/dir
fileutils-4.0i-1mdk
alien:~$

And the function works like this:

alien:~$ whichrpm dir
fileutils-4.0i-1mdk
alien:~$

function – tells bash that it’s function.
whichrpm – user defined name of the function.
{ / } – starts/ends the function
rpm -qf – command
` command quote
‘ precise quote
which – command to locate a file in your path
$1 – first argument after the function (the command after the function name
when you execute it).
; – end line
function whichrpm { rpm -qf `’which’ $1`; }

So when you execute this, the system will think.
aaah, a function within those {}’s, which I should call for when I hear
the word “whichrpm”, and what’s after that word ($1) will be used as
argument to “which”, and what that returns will be used after “rpm -qf”.

which works like this:

alien:~$ which dir
/usr/bin/dir
alien:~$

So “`’which’ $1`” (when executed with the word ‘dir’) returns “/usr/bin/dir”,
and so the whole function will finally execute: rpm -qf /usr/bin/dir

——————————————————————————-

Now more about the files in /etc, here you cant be user anymore,
to edit the files in /etc requires you to be root.

Fist here I’m going to talk about the /etc/crontab configuration file.

——————————————————————————-

The /etc/crontab is the global system file for cron jobs.
cron is short for chronological, and as the name tells it’s doing things
in a chronological order, as you can tell it to run a script or a program
once every 1 minutes, or you can tell it to run something annually, and
anything in between.

On RedHat like systems you have the dirs:

/etc/cron.daily/
/etc/cron.hourly/
/etc/cron.monthly/
/etc/cron.weekly/

Any script or program that lives in those files will execute by the last
name of the file, as if you put a script in /etc/cron.weekly/, the script
will execute weekly.

The /etc/crontab looks like this:

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly

The SHELL determens what shell that should be used to execute the things
in the crontab.

The PATH determens what directory’s it should look in for commands/programs
if no other specific path is given to a program, command or script.

The MAILTO variable determens to what user cron should send mails to on errors.

And the HOME variable determens crons root/home/base directory.

The first 5 fields determens when to run a job, here’s what they mean:

Field 1: minutes (0-59)
Field 2: hours (0-23)
Field 3: day of month (1-31)
Field 4: month (1-12 – or names)
Field 5: weekday (0-7 – 0 or 7 is Sun, or use names)

The next field is the user that owns the execution process.

Then we have run-parts, and after that the file to execute.
(if the file to execute is a dir, it will execute everything in it)

To use the crontab as a user (root included) simply type: crontab -e
This brings you to a VI like editor (see VI commands later in this tutorial).
Say now that you have a script /home/user/check.sh that you wanna run
every 5’th minute. then you type “crontab -e”
Press ‘Esc’ followed by ‘o’ to get to “insert” or “edit” mode.
In there make the following line:

0,5,10,15,20,25,30,35,40,45,50,55 * * * * /home/user/check.sh –flag

Then press ‘Esc’ followed by ‘:’ and then type ‘wq’ followed by enter to
write/save and, quit the file, and that’s it.

When you run crontab as user you don’t have to specify what user that should
own the process, “* * * * * file” should be enough.

Another way of writing:
0,5,10,15,20,25,30,35,40,45,50,55 * * * *       /home/user/check.sh –flag
Is this:
0-59/5 * * * *       /home/user/check.sh –flag
That means do this (/home/user/check.sh –flag) from 0-59 with 5 as an
intervall.
This means that:
* 0-23/2 * * *       /home/user/check.sh –flag
Would run the same script every other hour.

Not very hard is it ?

——————————————————————————-

Then we have the /etc/fstab is a list of the HD partitions the system
should mount as what when the system boots.
This may look like this:

/dev/hda1               /                       ext2    defaults        1 1
/dev/hda3               none                    swap    sw              0 0
/dev/hda4               /home                   ext2    defaults        1 2
/dev/hda6               /tmp                    ext2    defaults        1 2
/dev/hdc1               /windows                vfat    defaults        0 0
/dev/fd0                /mnt/floppy             auto    noauto,nosuid   0 0
/dev/hdb                /mnt/cdrom              auto    noauto,ro       0 0

Fist it’s the HD partition, then (a few tabs in) the mount point (where the
eventual contents of the HD partition should end up), then what file system
the partition has, further is if it should be mounted by default etc.
and the last 2 numbers is fs_freq and fs_passno (see the man page for fstab).

The possible HD partitions you have to find for your self or know…
a tip is to go over the HD’s with fdisk, and check for free space.

The possible mount points is only limited by your imagination, though
there must always be a /
A good disk usage should have these partitions:
/ 5%
/usr 30%
/home 30%
/tmp 10%
And 25% over for other partitions, like /sources, or whatever.

The possible and supported file systems are currenty:
minix,ext,ext2,xiafs,msdos,hpfs,iso9660,nfs,swap,vfat, and perhaps ntfs

The possible mount options are:
sync,user,noauto,nosuid,nodev,unhide,user,noauto,nosuid,exec,nodev,ro etc.
see the man mount page.

So say that you are going to add another cdrom that you want user to be able
to mount, and the cdrom is on /dev/hdd, then the line to add would look like
this (make sure you have the mount point dir, like here you have to
mkdir /cdrom):

/dev/hdd /cdrom auto noauto,user,ro 0 0

And that’s about it for the /etc/fstab

——————————————————————————-

Now I’d like to explain one of the very important files, the /etc/profile file.
In this file is the Global profile settings, that will apply for all users.

Fist in this file we should have the PATH variable.
The directory’s in the PATH is the directory’s the system will look in if you
type a command, for that command to execute it.

Say now that your path looks like this:
PATH=”$PATH:/usr/X11R6/bin:/bin”

And you type “ls”, then the system will first look in /usr/X11R6/bin if it can
find any file named “ls”, and if it doesn’t find it there, it will look in /bin,
and if it finds it there it will execute it.

The most common places on a system to store commands and programs is in these
directory’s:
/usr/X11R6/bin
/bin
/sbin
/usr/bin
/usr/sbin
/usr/local/bin
/usr/local/sbin

A path with all those directory’s in it would look like this:
PATH=”$PATH:/usr/X11R6/bin:/bin:/sbin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin”

The next thing in there can/should be the PS1 (the prompt), I’ve already
taken up how to customize the prompt, so no need to do that again.

Then (at least in RedHat like systems) we have this:

[ “$UID” = “0” ] && {
ulimit -c 1000000
} || {
ulimit -c 0
}

This says: if the UID of the user is 0 (root) then do: ulimit -c 1000000
or if that doesn’t work, do: ulimit -c 0.

Then we have an if statement about umask on the user…

After that we define some system variables, where after we export them.

Then we load all the .sh scripts in /etc/profile.d/

And that’s it, in that file.

This is an important file if you wanna add any system variables, or if you
want to change anything globally for the whole system.

——————————————————————————-

Now on to the /etc/hosts.allow and /etc/hosts.deny files.

Those hosts who are in hosts.allow are always allowed to connect to the system
under the condition that they have valid login and password ofcorse.

Those hosts who are in hosts.deny can never establish a lasting connection
to your system, even if they have a valid login and password.

If you don’t want anyone to connect to your computer at all, you simply add
the following to /etc/hosts.deny:

ALL: ALL

And this to /etc/hosts.allow:

ALL: LOCAL

Or if you have a network, you may wanna add this in /etc/hosts.allow:

ALL: LOCAL, 192.168.1.

Where 192.168.1. is your network call C network.

/etc/hosts.allow and /etc/hosts.deny understands the following wildcards:

ALL      The universal wildcard, always matches.
LOCAL    Matches any host whose name does not contain a dot character.
UNKNOWN Matches any user whose name is unknown.
KNOWN    Matches any user whose name is known.
PARANOID Matches any host whose name does not match its address.

Read man hosts.allow or man hosts.deny (should be the same man file), to find
out more about this.

——————————————————————————-

Next up is the /etc/inputrc file, which contains breaf keyboad confirurations.
If you want to something like Ctrl+W or something to a function of any kind
here is the place to do that.
The example from the file looks like this:

# Just a little exemple, how do you can configure your keyboard
# If you type Control-x s it’s add a su -c ” ” around the command
# See the info files (readline) for more details.
#
# “\C-xs”: “\C-e\”\C-asu -c \””

This would mean that if you want to add say: Ctrl+W to add the command
`time` before another command you would do:

“\C-w”: “\C-e\ \C-atime \

Another example would be, if you want to add: Ctrl+W Q to add: echo “<command>”
around the <command> you would do:

“\C-wq”: “\C-e\”\C-aecho \””

This means that if you type ‘word’ and then press Ctrl+W followed by Q you
will end up with: echo “word”, pretty handy.

You can also add a .inputrc in your home dir with the same functions,
but only for that user.

Just make sure you dont overwrite some other function, test the Ctrl+<key(s)>
function that you wanna use so they dont already do something.

If you want to bind keys to functions or characters, this is not the place
to do that, then you need to find your keymap like this one:
/usr/lib/kbd/keymaps/i386/qwerty/se-latin1.kmap.gz
gunzip it, edit it and then zip it up again.

I will not explain how to edit a keymap here, but it’s not that hard,
just read the contnts of the unziped keymap a few times and use the
power of deduction.

——————————————————————————-

The /etc/passwd holds the login information which looks something like this:

root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:
daemon:x:2:2:daemon:/sbin:
adm:x:3:4:adm:/var/adm:
lp:x:4:7:lp:/var/spool/lpd:
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
alien:x:500:500:Me:/home/alien:/bin/bash
user:x:501:501::/home/user:/bin/csh

You are looking on 7 accounts, nameley: root, bin, daemon, adm, lp, shutdown,
alien and user.

each of the lines have 7 feilds separated by ‘:’.
The fields from left to right are:

1 login-name
2 encrypted-password (this field contains only ‘x’ if there is an /etc/shadow)
3 uid (user id)
4 gid (group id)
5 user-information
6 home-directory
7 shell-type

If you make an account by hand in the /etc/passwd file, put a ‘*’ in the
encrypted-password field and use the `passwd` command to set the password.

——————————————————————————-

The /etc/shadow file, if this file exists, this is where the real
encrypted passwords are located, this file can only be read by the super-user
(root), and it looks like this:

root:$1$UrbUdguK$yrO3U/dlwKC5K3y2ON/YM.:11056:0:21:7:::
bin:*:11056:0:99999:7:::
daemon:*:11056:0:99999:7:::
adm:*:11056:0:99999:7:::
lp:*:11056:0:99999:7:::
shutdown:$1$hu86lnLIhnklY8ijnHui7.nn/jYg/mU:11056:1:365:14:::
alien:$1$vf3tGCFF$YRoFUgFDR8CVK6hHOwU/p0:11056:0:50:14:31::
user:$1$asd8kiLY76JNdskDkj97kMiyBujy/jD:11074:2:100:14:3::

(I’ve changed the characters in the encrypted-password, so they are not valid)

The manual page (man 5 shadow) tells the following about the 9 fields:

Login name
Encrypted password
Days since Jan 1, 1970 that password was last changed
Days before password may be changed
Days after which password must be changed
Days before password is to expire that user is warned
Days after password expires that account is disabled
Days since Jan 1, 1970 that account is disabled
A reserved field

If anyone knows what the last field (after the final ‘:’) is reserved for …
please drop me a mail.

Read the lines from the files, and compare them with what the 9 fields
mean, and see if you can make out how the accounts for each user is set up.

——————————————————————————-

Now the /etc/motd file.

The /etc/motd contains whatever you want to display to the user
that logs into the system, this can be a set of rules for your system,
or some ascii graphics or whatever you want.

——————————————————————————-

And now the /etc/skel/ which is a dir and contains the basic files
that will be given to any new user account.

Say that you add a file called, /etc/skel/.ircrc then all new useraccounts
that are added will have a ~/.ircrc file in there home directory.

——————————————————————————-

And last the /etc/issue and /etc/issue.net file.
On most systems there is only an /etc/issue file that works as both
/etc/issue and /etc/issue.net, the issue file holds the information
or rather text that is displayed to the user just before the
login prompt, usually it is the system specifications, like operating system
version and things like that.

The /etc/issue (if there is any /etc/issue.net) is the issue file for the
local users, and the /etc/issue.net is for users that logs in
from a remote host.

——————————————————————————-

There is alot more in the /etc directory, but what I’ve written this
far is about what you need to customize your system to your needs.

===============================================================================
7 – Networking.
===============================================================================

Linux is known to be one of the best networking operating systems in the
world, perhaps even THE best, unfortionally it’s not the easiest OS to
set up a good network in, but I hope that this section will make
exclamation marks out of some question marks.

——————————————————————————-

The first thing you need to do networking is 2 computers and
network cards attached with a crossed network cable, or connected via a hub,
with normal network cable (doh?).

The next step is to make sure the network cards work properly.

Make sure you have the networking support compiled into the kernel, you need
to have the following checked in the kernel (example is from the Linux 2.2.14
kernel, using `make menuconfig`, you can read more about how you
compile/recompile your kernel in /usr/doc/HOWTO/Kernel-HOWTO):

General setup —>
[*] Networking support
Networking options —>
[*] Kernel/User netlink socket
[*] Network firewalls
<*> Unix domain sockets
[*] TCP/IP networking
[*] IP: advanced router
[*] IP: firewalling
[*] IP: transparent proxy support
[*] IP: masquerading
[*] IP: ICMP masquerading
[*] IP: aliasing support
<*> IP: Reverse ARP
[*] IP: Allow large windows (not recommended if <16Mb of memory)
Network device support —>
[*] Network device support
Ethernet (10 or 100Mbit) —>
[*] Ethernet (10 or 100Mbit)
(In here find your network card and check it.)
Filesystems —>
[*] /proc filesystem support

Then you add this line in your /etc/rc.d/rc.local

echo “1” > /proc/sys/net/ipv4/ip_forward () at boot time

——————————————————————————-

If you have more then one network card, you may wanna add one as Module and
one hard compiled (*) into the kernel, so that the kernel knows that it’s
2 network cards.

Then you need to name then eth0 and eth1, this you *may* have to do
even if you only have 1 network card, but it’s not likely.

I have 2 network cards, one “3com 509 B” and one “3com 905”
The first thing I need to do is to is to find the module name for
the network cards.
Go to /lib/modules/2.2.14/misc/ and do an “ls”
(the 2.2.14/ dir will be named after whatever kernel version you have,
`uname -r` to find out)
In there I found a file called 3c59x.o (that’s the one I compiled as module),
then I set that as eth0, like this:
I open the file /etc/conf.modules (or /etc/modules.conf depending on the
kernel and system) and add:

alias eth0 3c59x

Then I know the other card is a “3com 509 B” so I go to:
/lib/modules/2.2.14/net/ and in there I find a 3c509.o, so I again
add an alias in /etc/conf.modules:

alias eth1 3c509

Basicly, you will find the network cards you added from the kernel in either
/lib/modules/2.2.14/net/ or /lib/modules/2.2.14/misc/, or say now
that you had a Linux 2.2.15 kernel then it would be:
/lib/modules/2.2.15/net/ and /lib/modules/2.2.15/misc/

And remember to add the cardnames without the .o in the module name, as
3c509.o will be named 3c509 as an alias in /etc/conf.modules.

——————————————————————————-

Now you wanna add the network card so it starts at boot time and get an IP.
Now you must decide what network IP it should have
(either 192.168.1.* or 10.0.0.* in this example I’ve used 10.0.0.*)
Open or crate a file called: /etc/sysconfig/network-scripts/ifcfg-eth0
(if it doesn’t exist when you open it it will be created.)

In this file type the following:

ONBOOT=yes
DEVICE=eth0
IPADDR=10.0.0.1
NETMASK=255.255.255.0
NETWORK=10.0.0.0
BROADCAST=10.255.255.255
BOOTPROTO=none

The save and quit.

ifcfg-eth0 goes if this is your first network card, if it were your second
network card on the same computer it would be ifcfg-eth1, and then the
DEVICE variable would say DEVICE=eth1.

——————————————————————————-

After this you need to tell your computer what IP, network name and nick name
it has. This you do in /etc/hosts.
By default you should have this line in your /etc/hosts:

127.0.0.1 localhost localhost.localdomain

Now you add your new hosts, the current computer and the other computer(s),
here I have used the 10.0.0.* IP range.

10.0.0.1 main.bogus.com main
10.0.0.2 sidekick.bogus.com sidekick

Note that there is a TAB separating each of the 3 fields (IP hostname nick).

——————————————————————————-

After that it’s time to set up the forwarding and everything like that using
ipchains.
This you do by adding the following lines to your /etc/rc.d/rc.local

/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -i eth0 -j MASQ

You may also wanna execute the lines since /etc/rc.d/rc.local only
loads at boot time.

——————————————————————————-

At this time you may also wanna set up a caching nameserver on your system,
Both to speed up your surfing and to get your LAN (Local Area Network)
to interact in a proper way.

In the following example I’ve used:

bind-8.2.2P5-1mdk.i586.rpm
and
caching-nameserver-6.0-3mdk.noarch.rpm

(A nameserver is depending on bind)

So after you installed bind and a caching-nameserver this is what you wanna do,
(everything in this example is based on the previously written network
configurations):

First you need to edit a file named /etc/named.conf, where in you add a “zone”.
The zones in this example to add, looks like this:

zone “bogus.com” {
type master;
file “bogus.com”;
};

zone “0.0.10.in-addr.arpa” {
type master;
file “10.0.0”;
};

The first one is for the networked computers hostnames, and the second for
there IP’s.

In this example I use 10.0.0.* as the network IP, but another common network
IP is also 192.168.0.* …. those are the two most common/accepted ones.

Then you save and quit that, to go and create the files bogus.com and 10.0.0,
which you do in: /var/named/

First we can create /var/named/bogus.com, and in there type the following:

@       IN      SOA     ns.bogus.com. main.bogus.com. (
                                       2000020100 ; Serial
                                       28800      ; Refresh
                                       14400      ; Retry
                                       3600000    ; Expire
                                       86400 )    ; Minimum
               IN      NS      localhost.
      ;1       IN      PTR     localhost.
localhost       A       127.0.0.1
ns              A       10.0.0.1
sidekick        A       10.0.0.2
main            A       10.0.0.1
mail            A       10.0.0.1

(What comes before the Serial, 2000020100 is a date, 2000-02-01-00, so
you can type that as your current date.)

Then you save and quit that, and crate the file: /var/named/10.0.0, and in
there you type this:

@       IN      SOA     ns.bogus.com. main.bogus.com. (
                                      2000020100 ; Serial
                                      28800      ; Refresh
                                      14400      ; Retry
                                      3600000    ; Expire
                                      86400 )    ; Minimum
                NS      ns.bogus.com.
1               PTR     main.bogus.com.
2               PTR     sidekick.bogus.com.

Now it’s almost time to start the nameserver, but first you wanna add the
nameserver to your /etc/resolv.conf so you have any use of it.

Open /etc/resolv.conf and at the top of it add:

nameserver 10.0.0.1

and leav the rest of the file entry’s as they are if there is any, then
save and quit that.

And now it’s time to start the nameserver.
To be sure that everything works normally, do these commands:

/usr/sbin/named
/usr/sbin/ndc restart

And then type `nslookup`, that should look like this:

root:~# nslookup
Default Server: main.bogus.com
Address: 10.0.0.1

If you get that, just type exit at the “>”, and then add the following lines
to /etc/rc.d/rc.local

if
ps aux | grep named | grep -v grep >/dev/null ; then
echo >/dev/null
else
/usr/sbin/named
/usr/sbin/ndc restart
fi

This will check if you have a named running, and if not, it will start it,
note that this is not the 100% correct way to do it, but it’s by far they
most lazy way to do it, and it works.

——————————————————————————-

That was the basics of making a network at home and setting up a nameserver.
I hope it’s enough so that anyone can set up a little network at home.

===============================================================================
8 – The Init and system scripts.
===============================================================================

In this section I will cover the system V init, which is the most used
init in Linux.
Beside the Syst V inti, there are also the BSD init, which is used by
Slackware and Debian and in some smaller distributions of Linux.
The rest, as far as I know, uses the Syst V init.
There are not so much difference of the two, I’ll try to cover the
differences later.
The example and files here are taken from SysVinit-2.78-6 & initscripts-5.27-37
which is compatible in some ways with the BSD init, I’ll come back to that
later.

So here we go:

——————————————————————————-

The basic Syst V init comes with the following commands & devices:

/dev/initctl This is the init controll device.
/sbin/halt This is to shut down the system.
/sbin/init This is to change the init runlevel.
/sbin/killall5 This will kill everything but the script that runs it.
/sbin/pidof This will get the PID of a Process name.
/sbin/poweroff This will power down the system.
/sbin/reboot This will reboot the system.
/sbin/runlevel This will tell the init runlevel.
/sbin/shutdown This will shut down the system.
/sbin/sulogin This is the single user mode login.
/sbin/telinit This is the init process control initialization.
/usr/bin/last This shows who was in the system last.
/usr/bin/lastb This is about the same as last.
/usr/bin/mesg This is to toggle writeble mode on your tty.
/usr/bin/utmpdump This dumps a file for utmp (this lacks documentation)
/usr/bin/wall This sends a message to all ttys.

And then the init needs the following extra files/dirs and commands from
the initscripts package:

/bin/doexec This lets you run a program under another name.
/bin/ipcalc This lets you manipulate IP addresses.
/bin/usleep This sleeps for microseconds.
/etc/X11/prefdm This is the display manager preferrence file for X.
/etc/adjtime This is the Kernel Clock Config file.
/etc/init.d BSD init compatibilety directory.
/etc/initlog.conf This is the initlog configuration file.
/etc/inittab This is the main init configuration file.
/etc/modules This is where the kernel loads modules from at boot.
/etc/ppp/ip-down This is a script for dialup internet connections.
/etc/ppp/ip-up This is a script for dialup internet connections.
/etc/profile.d/inputrc.csh Shell Key bindings for csh and tcsh.
/etc/profile.d/inputrc.sh Shell Key bindings for sh and bash.
/etc/profile.d/lang.csh Language files – i18n stuff for csh and tcsh.
/etc/profile.d/lang.sh Language files – i18n stuff for sh and bash.
/etc/profile.d/tmpdir.csh Set temporary directory for csh and tcsh.
/etc/profile.d/tmpdir.sh Set temporary directory for sh and bash.
/etc/rc.d/init.d/functions Functions for scripts in init.d
/etc/rc.d/init.d/halt Runlevel 0 (shutdown/halt) script.
/etc/rc.d/init.d/kheader Script to regenerate the /boot/kernel.h file.
/etc/rc.d/init.d/killall Script to make sure everything is shut off.
/etc/rc.d/init.d/mandrake_everytime Mandrake specific stuff.
/etc/rc.d/init.d/mandrake_firstime Mandrake post install stuff.
/etc/rc.d/init.d/netfs Mounts network filesystems.
/etc/rc.d/init.d/network Bring up/down networking.
/etc/rc.d/init.d/random Script to help random number generation.
/etc/rc.d/init.d/rawdevices Device stuff for applications such as Oracle.
/etc/rc.d/init.d/single Single user script (runlevel 1)
/etc/rc.d/init.d/sound Launch sound.
/etc/rc.d/init.d/usb Launch USB support.
/etc/rc.d/rc.local Boot time script, (like autoexec.bat in DOS).
/etc/rc.d/rc.modules Bootup script for modules.
/etc/rc.d/rc.sysinit Main system startup script.
/etc/rc.d/rc0.d/S00killall Runlevel 0 killall script link.
/etc/rc.d/rc0.d/S01halt Runlevel 0 halt script link.
/etc/rc.d/rc1.d/S00single Runlevel 1 single script link.
/etc/rc.d/rc2.d/S99local Runlevel 2 local script link. (rc.local)
/etc/rc.d/rc3.d/S99local Runlevel 3 local script link. (rc.local)
/etc/rc.d/rc4.d   Runlevel 4 directory.
/etc/rc.d/rc5.d/S99local Runlevel 5 local script link. (rc.local)
/etc/rc.d/rc6.d/S00killall Runlevel 6 killall script link.
/etc/rc.d/rc6.d/S01reboot Runlevel 6 reboot script link.
/etc/rc.local   BSD init compatibilety file…. ?
/etc/rc.sysinit   BSD init compatibilety file…. ?
/etc/rc0.d   BSD init compatibilety directory.
/etc/rc1.d   BSD init compatibilety directory.
/etc/rc2.d   BSD init compatibilety directory.
/etc/rc3.d   BSD init compatibilety directory.
/etc/rc4.d   BSD init compatibilety directory.
/etc/rc5.d   BSD init compatibilety directory.
/etc/rc6.d   BSD init compatibilety directory.
/etc/sysconfig/console Directory for console stuff, like the keymap.
/etc/sysconfig/init Basic init boot configurations.
/etc/sysconfig/network-scripts/ifcfg-lo Network config for localhost.
/etc/sysconfig/network-scripts/ifdown Turning off interfaces script.
/etc/sysconfig/network-scripts/ifdown-post Post stuff for ifdown.
/etc/sysconfig/network-scripts/ifdown-ppp Turning off ppp.
/etc/sysconfig/network-scripts/ifdown-sl Turning off SLIP.
/etc/sysconfig/network-scripts/ifup Turning on interfaces script.
/etc/sysconfig/network-scripts/ifup-aliases Turning on alias interfaces.
/etc/sysconfig/network-scripts/ifup-ipx Turning on IPX.
/etc/sysconfig/network-scripts/ifup-plip Turning on PLIP.
/etc/sysconfig/network-scripts/ifup-post Post stuff for ifup.
/etc/sysconfig/network-scripts/ifup-ppp Turning on ppp.
/etc/sysconfig/network-scripts/ifup-routes Turning on routes.
/etc/sysconfig/network-scripts/ifup-sl Turning on SLIP.
/etc/sysconfig/network-scripts/network-functions     Functions for the scripts.
/etc/sysconfig/rawdevices Raw device bindings.
/etc/sysctl.conf System Control configurations.
/sbin/consoletype This prints the console type.
/sbin/getkey   Prints the key strokes….
/sbin/ifdown   Application for the previous config files.
/sbin/ifup   Application for the previous config files.
/sbin/initlog   Logs msgs and events to the system logger.
/sbin/installkernel Installs a kernel (not for manual use).
/sbin/minilogd   * Totally lacking documentation.
/sbin/netreport   Reports changes of the network interface.
/sbin/ppp-watch   Application used by ifup-ppp.
/sbin/service   Can send commands to all services etc.
/sbin/setsysfont Sets the system font.
/usr/bin/listhome Lists the users home directorys.
/usr/sbin/detectloader Detect the current boot loader.
/usr/sbin/supermount Automatic mount/umount application.
/usr/sbin/sys-unconfig System reconfiguration tool.
/usr/sbin/usernetctl User Network interface control application.
/var/log/wtmp   Previously logged in users entrys.
/var/run/netreport Directory for the netreport application.
/var/run/utmp   Currently logged in users entrys.

So what do you really need to know of all that ?

Well, here’s the simple basics of how it works and what you need to remember.

The /etc/inittab is already explained.

——————————————————————————-

Here is how the runlevels works:

The Runlevel can be one of 1 to 6 and the number means this:

0 – halt
1 – Single user mode
2 – Multiuser, without NFS
3 – Full multiuser mode
4 – Unused
5 – X11
6 – reboot

You change the runlevel with the `init` command, so say that you are
int runlevel 3 and you wanna go to single user mode for some reason,
then you can do: init 1
In a single user mode you can only be one user, root.
And in a single user enviorment you can’t do networking and
other tasks, the runlevel 1 is meant to be there for system maintenence.

The two mostly used runlevels as default is 3 and 5.
Mandrake and RedHat etc. uses Runlevel 5 as default, and so they
start up with a GUI in X Windows.

Typing init 0 will shut down the system, and typing runlevel 6 will
reboot the system.

——————————————————————————-

What determes what the various runlevels actually start at boot time
is what is in there respective directory:

Runlevel 0: /etc/rc.d/rc0.d/
Runlevel 1: /etc/rc.d/rc1.d/
Runlevel 2: /etc/rc.d/rc2.d/
Runlevel 3: /etc/rc.d/rc3.d/
Runlevel 4: /etc/rc.d/rc4.d/
Runlevel 5: /etc/rc.d/rc5.d/
Runlevel 6: /etc/rc.d/rc6.d/

——————————————————————————-

So, here say that you wanna stop your web server from starting at boot time.
The first thing you wanna do is to find out what runlevel you are in, that
you do with the runlevel command like this:

alien:~$ runlevel
N 3
alien:~$

This means that you are in runlevel 3.
So from here go to /etc/rc.d/rc3.d/ which is the directory for runlevel 3.

alien:~$ cd /etc/rc.d/rc3.d/
alien: /etc/rc.d/rc3.d/ $

Here you find the file that starts the webserver (this file is usually
called httpd with a character and a number infront of it (I’ll explain the
character and the numbers soon), so list the contents of the current
directory and find it, or just do like this:

alien: /etc/rc.d/rc3.d/ $ ls -l *httpd
lrwxrwxrwx 1 root root 15 Dec 5 06:14 S85httpd -> ../init.d/httpd
alien: /etc/rc.d/rc3.d/ $

This says that S85httpd is a link to /etc/rc.d/init.d/httpd
(../init.d/ if you’re standing in /etc/rc.d/init.d/ mean /etc/rc.d/init.d/)

So just remove the link like this:

alien: /etc/rc.d/rc3.d/ $ rm -f S85httpd
alien: /etc/rc.d/rc3.d/ $

And that’s how you stop something from starting with the runlevel.

——————————————————————————-

Now, if you rather would have something more start with the runlevel
at boot time you do like this:

You make a simple script that starts what you wanna have started and
put it in /etc/rc.d/init.d/.
Say that your scripts name is “mystart”, you are in runlevel 3 and you have
made your script executable (chmod a+x mystart), and you have it
in your own home directory, then you do like this:

alien: ~$ cp mystart /etc/rc.d/init.d/
alien: ~$ cd /etc/rc.d/rc3.d
alien: /etc/rc.d/rc3.d/ $ ln -s ../init.d/mystart Z00mystart
alien: /etc/rc.d/rc3.d/ $

And that’s all of that.

So now, what does the Z00 in Z00mystart or S85 in S85httpd mean ?
Well, as the system starts it will read file after file in it’s runlevels
directory in alphabetical order, so to get them to start in a preticular
order, the link names are made to determen that order.
So the later in the alphabet the first character is the later it will boot,
and the same for for the number, the higher number the later it will start.

So A00something will start before A01something
And Z99something will start later then X99something and so on.

To get something to start at boot time you can also add it as a command
in the /etc/rc.d/rc.local (or for some systems /etc/rc.local) file.
That file is meant to be used for single commands and not to start up
major things like a server etc.

Always try to load things with the actual runlevel which is the more correct
way, rather then adding them to the rc.local file

——————————————————————————-

So what’s the difference between the BSD init and the System V init ?
The only thing that differs them that you need to rememer is that they
store the startup scripts in different places.

The startup scripts for the BSD init is mainly in the following places:

/etc/rc0.d/
/etc/rc1.d/
/etc/rc2.d/
/etc/rc3.d/
/etc/rc4.d/
/etc/rc5.d/
/etc/rc6.d/
/etc/rc.boot/
/etc/rcS.d/
/etc/init.d/

While the Syst V init stores its scripts mainly in:

/etc/rc.d/rc0.d/
/etc/rc.d/rc1.d/
/etc/rc.d/rc2.d/
/etc/rc.d/rc3.d/
/etc/rc.d/rc4.d/
/etc/rc.d/rc5.d/
/etc/rc.d/rc6.d/
/etc/rc.d/init.d/

In the BSD init the /etc/rc.boot/ and the /etc/rcS.d/ directorys
are more or less substitutes for the rc.local file since you can
put things in them that starts up at boot time…
what you put in /etc/rcS.d/ will even start at single user mode,
so be careful what you put there.

So basically, the actual scripts goes in the init.d directory
and you link them to the runlevel directory with a prefix to determen where
in the bootup they should be loaded.

——————————————————————————-

Here is an example of how an init script can be made.
Here I made a script that would start a daemon named “daemon”

——————————————————————————-

#!/bin/sh
# example Example init script that would load ‘daemon’
#
# Version: @(#) /etc/rc.d/inet.d/example 0.01 19-Feb-2001
#
# Author: Billy (Alien), <alien@ktv.koping.se>
#

. /etc/rc.d/init.d/functions

function status() {
ps aux | grep daemon &&
echo “Daemon is running.” ||
echo “Daemon is not running.”
}

case “$1” in
    start)
    # Check if daemon is in our path.
    if `which daemon` > /dev/null; then success || failure; fi
    echo -n “Starting Daemon”
daemon
    echo
   ;;
    stop)
    # Check if daemon is in our path again.
    if `which daemon` > /dev/null; then success || failure; fi
    echo “Stopping Daemon”
killall -15 daemon
   ;;
    status)
    echo “Status of Daemon:”
status
   ;;
    reload)
    echo “Restarting Daemon.”
killall -1 daemon
   ;;
    restart)
    if `which echo` > /dev/null; then success || failure; fi
    $0 stop
    $0 start
   ;;
    *)
    echo “Usage: $0 start|stop|restart|status”
    exit 0
esac

——————————————————————————-

A note is that the success and failure functions/commands come from
the /etc/rc.d/init.d/functions file, which may not be present in all
distributions of Linux, since it as far as I know only comes with
RedHat and Mandrake.

——————————————————————————-

The inits main configuration file is the /etc/inittab file, here is where
you set which runlevel you you wanna have, and how many consoles you want
etc, so here we go:

The line where you actually set the runlevel looks like this (here runlevel 3):

id:3:initdefault:

Most RedHat like systems have runlevel 3 or 5 as default, but if you don’t
have any networking, you may find it better to change to runlevel 2.

Next in this file should be the system initialization.

si::sysinit:/etc/rc.d/rc.sysinit

This line tells the system the path to the rc.sysinit where it loads
alot in the system, as system clock, sets the hostname, and
performs a number of checks.

Next in line is this:

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

This tells the system where to load the programs and daemons it should load
for the runlevel it’s in.
Say that we are in runlevel 3 (Default) then it looks at this line:

l3:3:wait:/etc/rc.d/rc 3

And there after goes to load all what’s in /etc/rc.d/rc3.d/
(rc3.d or any rc?.d contains links to the real files or scripts
that’s located in /etc/rc.d/init.d, so if you wanna add something to
your runlevel, just look how they have done it and do it in a similar fashion.
and make sure to not start any network dependent application before the
network starts and so on…)

Then it comes some other various stuff as trap the Ctrl+Alt+Del etc.

After this comes the tty’s (Terminal Types), and there locations.

1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

If you wanna add some more you can add like this:

8:2345:respawn:/sbin/mingetty tty8
9:2345:respawn:/sbin/mingetty tty9
10:2345:respawn:/sbin/mingetty tty10
11:2345:respawn:/sbin/mingetty tty11

And leav tty7 reserved for X-windows.

Last in the file should only be some line about xdm and it’s location,
this is if you have xdm installed…

——————————————————————————-

And if you have read the tutorial to this point you shouldent need any real
explanation of this script.

If you still dont understand how the init scripts work, read the
scripts in your system and try to understand them.
And also read this section about the init and the init scripts again.

===============================================================================
9 – Basic Linux/UNIX commands and operations.
===============================================================================

This section is about Linux and UNIX basic commands and operations, and some
other explanations and tricks, since this is not a command bible,
I’ll explain each command breafly, with alot of help from the
man pages and the –help argument (let’s all thank the maker for cut & paste).
Then again, I’ve seen files that have claimed to be UNIX command bibles
that are even breafer and hold less commands… though most of the authors
of those seems to be totally uncapeble of handling a UNIX and cant even spell,
one of the worst examples I’ve seen was something like this:
“The UNIX bible, in this phile is all the UNIX commandz j00 need”
And after that was a list of commands without arguments… needless to say
is also that 99% of all UNIX commands were missing.
Anyway, enough of me making fun of those people now, and on with the tutorial.
(Which isn’t a UNIX command bible, just a note)
I will refer to “*nix” here, and that means any sort of UNIX system,
Linux, BSD, Solaris, SunOS, Xenix and so on included.

——————————————————————————

Here are the basic *nix commands, with breaf explanations.

——————————————————————————

adduser
Syntax: adduser [arguments] <user>
And can be used with the following arguments:
-u uid
-g group
-G group,…
-d home directory
-s shell
-c comment
-k template
-f inactive
-e expire mm/dd/yy
-p passwd
Then there are a few arguments with no explanation:
-o, -m, -n, and -r
So say that you wanna add a user named “user” with password “resu”
belonging to the group root with / as home directory using /bin/tcsh
as shell, that would look as this:

adduser -p resu -g root -d / -s /bin/tcsh user

——————————————————————————

alias
The alias command set’s an alias, as this: alias du=’du -h’
This means that whenever you type: du
it will really do: du -h

Typing alias by it self will display all set aliases.

For more information on the alias command do: help alias

——————————————————————————

apropos
apropos checks for strings in the whatis database. say that you
        are looking for a manual page about the `shutdown` command.
        Then you can do: apropos shutdown
        for more information, do: man whatis
        Or: man apropos

——————————————————————————

awk
awk is a text formatting tool, that is HUGE, it’s actually a whole
language, some say it’s not totally wrong to say that awk is not
far off from a scripting version of C.
However I wouldent go as far as to say that there resemblance
is that great.
awk’s most common use is about the same as ‘cut’, and it works like
this: awk [argument-1] [argument-2] ….
Here’s some example’s of converting an URL:

echo “http://www.bogus.com/one/two.htm” | awk -F’/’ ‘{print $3}’
This will return: www.bogus.com
The -F will set a delimiter, and the ‘{print $3}’ will print the
third feild, separated by the delimiter, which is www.bogus.com,
because there is 2 slashes, which makes the second slash the second
feild, and so www.bogus.com is the third feild.
Here’s another example:

echo “http://www.bogus.com/one/two.htm” | awk -F’/’ ‘{print $(NF)}’
This will return: two.htm
The -F set’s the delimiter, which once again is /, but this time
we have used $NF which always resembles the last feild.
Another example with NF is this:

echo “http://www.bogus.com/one/two.htm” | awk -F’/’ ‘{print $(NF – 1)}’
This will return: one
Because $(NF – 1) means the last feild minus one feild, which always
will be the next last feild.

You only have to use the ()’s around variables when you do something
with them like here “$(NF – 1)”, but you can use $(var) all the time
if you want.

Here’s another example:

echo “http://www.bogus.com/one/two.htm” | awk -F’/’ ‘{print $3 “/” $(NF – 1)}’

This will return: www.bogus.com/one
It will first print out the third feild separated by /’s, which is
www.bogus.com, then it will print a /, and then it will print out
the next last feild which is one.

Here is a very shoer final example of awk:

echo “http://www.bogus.com/one/two.htm” | awk ‘{ while ( $(1) ) print }’

This will return: “http://www.bogus.com/one/two.htm” forever.
The “while ( $(1) )” means that as long as there is first feild,
it will print the line line.
And since there will always be a first feild it will continue
forever.
while in awk works as this: while ( condition ) action

As I said, awk is huge and is actually a whole language, so
to explain all of it it would need a tutorial of it’s own.
So I will not go any deeper into awk here, but you can as always
read it’s manual page which is quite large.

So, for more info do: man awk

——————————————————————————

basename
basename will strip directory and suffix from filenames.
This command only have the two following flags:

–help display this help and exit
–version output version information and exit

It works like this:
alien:~$ basename /usr/local/bin/BitchX -a
BitchX
alien:~$ basename http://www.domain.com/path/to/file.html
file.html
alien:~$

For more info do: man basename

——————————————————————————

bc
A precision calculator, can be used with the following arguments:
       -l     Define the standard math library.
       -w     Give warnings for extensions to POSIX bc.
       -s     Process exactly the POSIX bc language.
       -q     Do not print the normal GNU bc welcome.
       -v     Print the version number and copyright and quit.

——————————————————————————-

BitchX
BitchX is usually not default on any system, but it’s the far
msot advanced IRC client to *nix.
BitchX started as a script to ircii (ircii is irc2 an extended
irc protocol, also EPIC which is more bareboned then BitchX is
made from ircii), until BitchX got hard coded to the protocol
in C, by panasync I belive.

BitchX has alot of arguments but can be executed without any
arguments.
This is the synatx: BitchX [arguments] <nickname> <server list>
And here are the arguments anyway:

-H <hostname> this is if you have a virtual host.
-c <#channel> auto join a channel, use a \ infront of the #
-b load .bitchxrc or .ircrc after connecting to a server
-p <port> connect on port (default is 6667)
-f            your terminal uses flow controls (^S/^Q),
   so BitchX shouldn’t
-F            your terminal doesn’t use flow control (default)
-d dumb terminal mode (no ncurses)
-q dont load the rc file ~/.ircrc
-r <file>       loads file as list of servers to connect to
-n <nickname> set the nickname to use
-a              adds default servers and command line servers
   to server list
-x           runs BitchX in “debug” mode
-Z              use NAT address when doing dcc
-P              toggle check pid.nickname for running program
-v show client version
-B              fork BitchX and return you to shell. pid check on.
-l <file>     loads <file> in place of your ~/.ircrc
-L <file>     loads <file> in place of your .ircrc and
   expands $ expandos

The most common way of starting BitchX is this, say that you want
to have the nick ‘Bash’ on server irc.bogus.com, then you can do:

BitchX Bash irc.bogus.com

There is so much to say about BitchX that it would need a tutorial
of it’s own, I’m currently writing a BitchX script, so maybe
I’ll write a BitchX tutorial some time =)

——————————————————————————-

bzcat

bzcat will uncompress a .bz2 file ‘on the fly’ as it cat’s it.
the actual file will remain compressed after bzcat has displayed
the contents.
bzcat has to my knowlidge only one switch, and that’s
-s, that uses less memory.
bzcat works like this:

bzcat file.bz2

This can be good if you wanna search something in a text file
that has been bzip2’d.
Examples:

bzcat file.bz2 | grep ‘text string’
bzcat file.bz2 | wc -l

——————————————————————————-

bzip2

Compression tool, compresses harder then the standard gzip.
bzip2 can be used with the following arguments:
-h –help           print this message
-d –decompress     force decompression
-z –compress       force compression
-k –keep           keep (don’t delete) input files
-f –force          overwrite existing output files
-t –test           test compressed file integrity
-c –stdout         output to standard out
-q –quiet          suppress noncritical error messages
-v –verbose        be verbose (a 2nd -v gives more)
-L –license        display software version & license
-V –version        display software version & license
-s –small          use less memory (at most 2500k)
-1 .. -9            set block size to 100k .. 900k
Normally used as: bzip2 -d file.bz2 (to decompress a file)
or bzip2 -z file (to compress a file)

——————————————————————————-

cat
cat followed by a filename will bring the contents of the file
out to the screen (stdout), and can be used with the following
arguments:
-A, –show-all           equivalent to -vET
-b, –number-nonblank    number nonblank output lines
-e                       equivalent to -vE
-E, –show-ends          display $ at end of each line
-n, –number             number all output lines
-s, –squeeze-blank      never more than one single blank line
-t                       equivalent to -vT
-T, –show-tabs          display TAB characters as ^I
-u                       (ignored)
-v, –show-nonprinting   use ^ and M- notation, except for LFD and TAB
–help               display this help and exit
       –version            output version information and exit

——————————————————————————-

cc
C compiler, can be used with ALOT of arguments, do a man cc to find
out just how many, it’s normally used to compile a .c source file to an
executable binary, like this:
cc -o program program.c

——————————————————————————-

cd
change directory, works as this:
cd /way/to/directory/I_want_to/be/in/

No further explanation needed.

——————————————————————————-

chattr
This is a very powerful command with which you can change the
attributes on an ext2 file system.
This means that you can make a file impossible to remove
for as long as the attributes are there.

The attributes that can be added or removed are the follwoing:

A Don’t update atime.
S Synchronous updates.
a Append only.
c Compressed.
i Immutable.
d No dump.
s Secure deletion.
u Undeletable.

So here is an example:

chattr +iu /etc/passwd

This makes it impossible to remove the /etc/passwd file unless
you first do:

chattr -iu /etc/passwd

This can also be good for the logs, esecially, with the a attribute.
To see the attributes, use: lsattr

For more info do: man chattr

——————————————————————————-

chmod
chmod is a very useful command, it changes the rights of any file.
To understand this command you need to understand how the permission
line works:

-rwxr-xr-x 1 alien users 58 Feb 7 13:19 file1
-rw-r–r– 1 alien users 3.1k Feb 3 15:47 file2

Let’s break the -rwxr-xr-x down into 4 sections:
– rwx r-x r-x
The first – you can not change, that tells what sort of file it is,
as if it’s a special file, a directory or a normal file.
The second rwx is the rights of the owner of the file.
The third r-x is the rights the group of the file has.
And the fourth r-x tells us what right others/anyone else has.
The rights can be:

r read rights.
w write rights.
x execute rights.
s suid (su id, execute with someome else’s uid, usually root)
t saves the programs text on the swap device
X executes file only if it’s in a dir that has execute rights

Then we need to know in what of those 3 last fields to set those
rights, they can be set to:

a all (changes the 3 fields syncroniously)
u user
g group
o others/anyone else

You can add or remove rights with the following arguments:

+ add a right
– remove a right
= absolute right

So say now that we have a file called file1, that looks like this:

-rwxr-xr-x 1 alien users 58 Feb 7 13:19 file1

And we wanna take away all execution rights.
Then we can either do:
chmod a-x file1
or
chmod ugo-x file1
And if we wanna make a file executable to everyone in it’s group,
in this case the group “users”, then we do:
chmod g+x file1

The other way to do this, is to use octal numbers to set the
rights in the permission line.
This requires a bit more thinking if your not use to it, but here’s
how it works:

First we break up the permission line into 3 sections again (not
counting the leading – or d), and then we put numbers on each
of the 3 fields in each of the 3 sections.

– rwx rwx rwx
421 421 421

Now to change a line to say: -rwxrx-r-x
You would:
x and r in the last field, that would mean 1+4=5, then the same thing
in the middle field, and last we have r, w and x in the first so then
we count them all, 1+2+4=7.
If we now line up our results of this little mathematic we get: 755
And so to change a permission line to -rwxrx-r-x we do:

chmod 755 <file>

Here’s how it looks:

Oct Bin Rights

        0         0 —
        1         1 –x
        2        10 -w-
        3        11 -wx
        4       100 r–
        5       101 r-x
        6       110 rw-
        7       111 rwx

Then we have the suid stuff for this with octal counting, that you set
before the normal rights, I’ll explain that in a bit, first here
is the number codes for the special options as suid.

7*** SUID (user & group and set’s file +t)
6*** SUID (user & group)
5*** SUID +t (saves the files text to the swap partition and SUID user)
4*** SUID (user)
3*** SUID (group and set’s file +t)
2*** SUID (group)
1*** +t (saves the files text to the swap partition)
0*** nothing

Here’s how it looks:

Oct Bin    Rights
– — rwx rwx rwx
0     0 — — —
1   1 — — –t
2 10 — –s —
3 11 — –s –t
4 100 –s — —
5 101 –s — –t
6 110 –s –s —
7 111 –s –s –t

So if you have a file that we can call ‘foo.sh’ and you wanna make
so that only the user has write permissions to it, the user
and group has read and execute permissions, and all others has no
rights at all to it.

Then we would count: others, 0, group 5, user 7, and then to SUID
the group we add a 2 in front of what we have, which means:

chmod 2750 foo.sh

This will make foo.sh’s permission line look like this:

-rwxr-s—

To do the exact same with characters, you do:

chmod u+rwx,go-rwx,g+s foo.sh

The most common premissions for files is

Executeble: (755) -rwxr-xr-x
Non-Executeble: (644) -rw-r–r–

The easyest way of setting these is by eather do:

chmod 755 file
or
chmod =rwxrxrx file

chmod 644 file
or
chmod =rwrr file

For more information, do: man chmod

——————————————————————————-

chown
chown changes owner of a file, it can actually also change the group.
it works like this:

chown user file

This would change the owner of the file to user, but note that
you can not change to owner of a file to a user that’s owned
by someone else, same thing is that you can not change another
users files so that you own them.
Basicly, you need to be root to for this command in most cases.
If you wanna change both the user and the group of a file, you do
like this:

chown user.group file

That would change the owner of the file to user and the group
of the file to group.
For more info on this do: man chown

——————————————————————————-

chroot
runs a command or interactive shell with special root directory.
It works like this:

chroot /new/root/directory/ command

This can be good for some programs or commands, that rather
would have / as root directory then ~/ etc.

——————————————————————————-

cmp
compares 2 files for differences, it can be used with the
following arguments:

-l Print the byte number (decimal) and the differing byte
values (oc- tal) for each difference.

-s Print nothing for differing files; return exit status only.

It works like this:

cmp file1 file2
Or
cmp -s file1 file2

Not a very big, but still useful command.

——————————————————————————-

cp
copy, copy’s a file from one location to another, may also copy
one filename to another, used as this:
cp file /some/other/dir/
or
cp file file.old

——————————————————————————-

crontab
Crontab has already been explained in this tutorial.

——————————————————————————-

cut
cut is a very powerful command, that allows you to cut in texts,
It works like this: cut [arguments] <file>

-b, –bytes=LIST
output only these bytes

-c, –characters=LIST
output only these characters

-d, –delimiter=DELIM
use DELIM instead of TAB for field delimiter

-f, –fields=LIST
output only these fields

-n
(ignored)

-s, –only-delimited
do not print lines not containing delimiters

–output-delimiter=STRING
use STRING as the output delimiter

the default is to use the input delimiter

–help
display the help and exit

–version
output version information and exit

One of the many ways to use it is like this, say that you have a file
named “hostlist” that contains this:

beta.linux.com has address 216.200.201.197
shiftq.linux.com has address 216.200.201.195
irc.linux.com has address 216.200.201.199
oreilly.linux.com has address 208.201.239.30
srom.linux.com has address 204.94.189.33
admin.linux.com has address 216.200.201.194

And you ONLY wanna list the IP’s from it, then you do this:

cut -d ‘ ‘ -f 4 testfile

That will output only the IP’s, first we set the delimiter to ‘ ‘
which means a space, then we display the 4’th field separated by
the delimiter, which here is the IP’s.

Or that you have a file (say named column.txt) that contains this:

something                if we have to
or someone              cut and paste
likes to write          the columns.
in columns, we          So what do
don’t like that          we do about
especially not          this ?

To cut out each column is done like this:

cut -c 1-14 column.txt
cut -c 23-40 column.txt

This would fist cut the file lengthwise and display characters
1-14 and then the same thing again but characters 23-40.

Now a simple way to get them in a long row instead of columns
in a file is this:

cut -c 1-14 column.txt > no-columns.txt
cut -c 23-40 column.txt >> no-columns.txt

——————————————————————————-

date
date alone returns the current date and time in the following format:

day month date hr:min:sec timezone year

But can be executed with the following arguments:

%%   a literal %
        %a   locale’s abbreviated weekday name (Sun..Sat)
%A   locale’s full weekday name, variable length (Sunday..Saturday)
   %b   locale’s abbreviated month name (Jan..Dec)
   %B   locale’s full month name, variable length (January..December)
   %c   locale’s date and time (Sat Nov 04 12:02:33 EST 1989)
   %d   day of month (01..31)
   %D   date (mm/dd/yy)
   %e   day of month, blank padded ( 1..31)
   %h   same as %b
   %H   hour (00..23)
   %I   hour (01..12)
   %j   day of year (001..366)
   %k   hour ( 0..23)
   %l   hour ( 1..12)
   %m   month (01..12)
   %M   minute (00..59)
   %n   a newline
   %p   locale’s AM or PM
   %r   time, 12-hour (hh:mm:ss [AP]M)
   %s   seconds since 00:00:00, Jan 1, 1970 (a GNU extension)
   %S   second (00..60)
   %t   a horizontal tab
   %T   time, 24-hour (hh:mm:ss)
   %U   week number of year with Sunday as first day of week (00..53)
   %V   week number of year with Monday as first day of week (01..52)
   %w   day of week (0..6); 0 represents Sunday
   %W   week number of year with Monday as first day of week (00..53)
   %x   locale’s date representation (mm/dd/yy)
   %X   locale’s time representation (%H:%M:%S)
   %y   last two digits of year (00..99)
   %Y   year (1970…)
   %z   RFC-822 style numeric timezone (-0500) (a nonstandard extension)
   %Z   time zone (e.g., EDT), or nothing if no time zone is determinable

For example, if you want to the time as hr:min:sec day, you would do:

date +’%H:%M:%S %a’

Or if you wanted to display the name of the month only, you would do:

date +%B

——————————————————————————-

dc
dc is an arbitrary precision calculator.
man dc for more info.

——————————————————————————-

dd
disk duplicator, this is a very powerful command, that is
useful for doing backups as well as creating boot floppy’s
from images.
Say now that you have a Slackware standard boot floppy image (bare.i)
and you want to write it to a floppy, then you do this:

dd if=bare.i of=/dev/fd0 conv=sync

If you instead have a RedHat or Mandrake boot image, just replace
the bare.i in the line with boot.img, under the condition that
you are standing in a directory that contains that specific image.

The conv=sync part is just there to make sure that the disks are
synced.

dd is a quite big command so I suggest you take a look at the man page.

——————————————————————————-

declare
declare will declare a variable and may set attributes to it.
The attributes declare can set or use with the following flags are:

        -p        show variable with attributes.
        -a        to make a variable(s) an array (if supported)
        -f        to select from among function names only
        -F        to display function names without definitions
        -r        to make variable(s) readonly
        -x        to export variable(s)
        -i        to make variable(s) have the `integer’ attribute set

Using `+’ instead of `-‘ turns off the given attribute(s) instead
of setting them.
If declare is used within a function, the variables will be
local, the same way as if the `local` command had been used.

The -r option works the same as the `readonly` command.
And the -r option can not be removed once it’s set.

Here’s a short example:

declare -xr foo=bar

This would do the same as to do:

export foo=bar; readonly foo

For more info on this, do: help declare

——————————————————————————-

depmod
depmod loads kernel modules, and is a very powerful command,
it’s greatest use is that it can reload all kernel modules
in a single line:

depmod -a

This is especially good if you have recompiled some modules and
installed them, and you don’t wanna reboot the system.
The command also allows you to load single modules or several
modules, like this:

depmod module1.o module2.o … etc.

For more info, man depmod

——————————————————————————-

df
Reports filesystem disk space usage.
df can be used with the following arguments:

-a, –all
include filesystems having 0 blocks

–block-size=SIZE use SIZE-byte blocks

-h, –human-readable
print sizes in human readable format (e.g., 1K 234M 2G)

-H, –si
likewise, but use powers of 1000 not 1024

-i, –inodes
list inode information instead of block usage

-k, –kilobytes
like –block-size=1024

-l, –local
limit listing to local filesystems

-m, –megabytes
like –block-size=1048576

–no-sync
do not invoke sync before getting usage info (default)

-P, –portability
use the POSIX output format

–sync invoke sync before getting usage info

-t, –type=TYPE
limit listing to filesystems of type TYPE

-T, –print-type
print filesystem type

-x, –exclude-type=TYPE
limit listing to filesystems not of type TYPE

-v (ignored)

–help display this help and exit

–version
output version information and exit

My favorite is to use: df -h

——————————————————————————-

dhcpcd
dhcpcd is used to obtain an IP if you have dynamic IP on a LAN
such as a cable modem with dynamic IP.

——————————————————————————-

dialog
The dialog command has already been explained in this tutorial.

——————————————————————————-

diff
diff is a very large command that finds the difference between
two files, it’s very handy to have to make patches.
The basic use of diff is as follows:
diff file1 file2
for more and full info on this command, do: man diff

——————————————————————————-

dir
Same as “ls”.

——————————————————————————-

dmesg
dmesg can print or control the kernel ring buffer.
by default it’ll show a log of loaded and unloaded modules
and other kernel events, like initialization if RAM disks etc.
(this is flushed at each reboot)
This is useful to make a boot.messages file, bu simply doing this:
dmesg > boot.messages
If there is any errors at the boot up this command is the first
you would use to try to determen the error.

This is the syntax of dmesg (cut’n’paste of the man page):

dmesg [ -c ] [ -n level ] [ -s bufsize ]

The options (-c/-n/-s) means the following:

-c
clear the ring buffer contents after printing.

        -s bufsize
               use a buffer of bufsize to query the kernel ring
               buffer. This is 8196 by default (this matches the
               default kernel syslog buffer size in 2.0.33 and
               2.1.103). If you have set the kernel buffer to
               larger than the default then this option can be
               used to view the entire buffer.

        -n level
               set the level at which logging of messages is done
               to the console.   For example, -n 1 prevents all
               messages, expect panic messages, from appearing on
               the console.   All levels of messages are still
               written to /proc/kmsg, so syslogd(8) can still be
               used to control exactly where kernel messages
               appear. When the -n option is used, dmesg will not
               print or clear the kernel ring buffer.

When both options are used, only the last option on
the command line will have an effect.

An example of usage is this:

dmesg -c -s 16392

This would print the kernel ring buffer (with a buffer size of 16392)
And then flush the contents.

For more info on this command do: man dmesg

——————————————————————————-

do
do just does what it says, and is used in among others
‘while’ loops, if you have read the whole tutorial this far
(and have photographic memory) you understand what I’m saying.

——————————————————————————-

domainname
See hostname.

——————————————————————————-
du
du shows estimated file space usage.
du is a good command to show how much space a directory takes up.
I prefer to use it with the -h argument (human readable, see df).
du has lots of arguments, do `man du` for a full list.

——————————————————————————-

echo
echo will redisplay anything you put after it.
This is perhaps the most used command in bash scripting, and
very useful in everyday *nix handling as well, I’ll get back
to that in a moment. but first, echo has the following arguments:

-n do not output the trailing newline

-e enable interpretation of the backslash-escaped characters
listed below

-E disable interpretation of those sequences in STRINGs

–help display this help and exit (should be alone)

–version
output version information and exit (should be alone)

AND these:

e       backslash
        c       suppress trailing newline
        a       alert (BELL)
        f newline and vertical tab
n new line
r delete recursively (rest of line backwards)
t vertical tab
v newline and vertical tab (vertical tab ?)
xa new line
xb newline and vertical tab
xc newline and vertical tab
xd delete rest of line forward
xe ascii … screws up the console (type reset to get it back)

So to get a bell (beep) you just do:

echo -e “\a”

Or to screw up your console, do:

echo -e “\xe”

——————————————————————————-

eject
With eject you can eject removable medias, such as tapes, JAZ, ZIP,
CD-rom and so on.
The command is pretty self explanatory, and can be used with the
following arguments:

-h –help
        -v –verbose
        -d –default
        -a –auto
        -c –changerslot
        -t –trayclose
        -n –noop
        -r –cdrom
        -s –scsi
        -f   –floppy
        -q –tape

The eject command is used as follows: eject [argument] <name>
The name is the name of th drive, either from /dev, /mnt or
by it’s mountpoint name.

——————————————————————————-

else
Used in ‘if’ statements, and does what it says, used like this:
if [ “arg1” = “arg2” ]; then echo “match” ; else echo “no match” ; fi

——————————————————————————-

env
Display the enviorment settings.
Can be used with the following arguments:
       -i, –ignore-environment. start with an empty environment
       -u, –unset=NAME. remove variable from the environment
       –help display this help and exit
       –version

——————————————————————————-

exit
exit is used to kill the current process.
It can either be used to logout or to kill a running script from
within the script, in the later case it can be used with a
return number as argument, ie. exit 0

——————————————————————————-

expr
expr is a counter or command line calculator, it can handle most
simple integer calculations.
It can use all the normal ways of counting including boolean
operators, such as | OR, != NOT IS, and so on.
It’s simply used as this: expr 1 + 1
One thing to remember, since this is in the command line, if you use
* (times), you have to use it like this: expr 2 ‘*’ 2
The ‘ precise quote makes sure that the star is not treated
as a wildcard.

——————————————————————————-
fdisk
fdisk is the classic disk handler, with fdisk you can edit your
hard drive(s) in alot of ways, as adding or removing partitions,
list the partitions and so on.
You start fdisk as this: fdisk /dev/<disk to veiw/edit>
This may be a disk such as /dev/hda /dev/hdb /dev/hdc and so on.
Note that you can not determen a specific HD partition to
start from, since fdisk operates on the whole HD.

When you start fdisk you will have the following commands,
followed by there explanation:

    a   toggle a bootable flag
    b   edit bsd disklabel
    c   toggle the dos compatibility flag
    d   delete a partition
    l   list known partition types
    m   print this menu
    n   add a new partition
    o   create a new empty DOS partition table
    p   print the partition table
    q   quit without saving changes
    s   create a new empty Sun disklabel
    t   change a partitions system id
    u   change display/entry units
    v   verify the partition table
    w   write table to disk and exit
    x   extra functionality (experts only)

And in ‘x’ the extra functionality (experts only) mode.

    b   move beginning of data in a partition
    c   change number of cylinders
    d   print the raw data in the partition table
    e   list extended partitions
    g   create an IRIX partition table
    h   change number of heads
    m   print this menu
    p   print the partition table
    q   quit without saving changes
    r   return to main menu
    s   change number of sectors/track
    v   verify the partition table
    w   write table to disk and exit

For more info on fdisk, do: man fdisk

——————————————————————————-

file
The file command will tell you what type of file a file is.
file basically works like this:
file [ -bciknsvzL ] [ -f namefile ] [ -m magicfiles ] file
The options are as follows:

-b Do not prepend filenames to output lines (briefmode).

        -c      Cause a checking printout of the parsed form of
                the magic file. This is usually used in conjunction
                with -m to debug a new magic file before installing it.

        -f namefile
                Read the names of the files to be examined from
                namefile (one per line) before the argument list.
                Either namefile or at least one filename argument
                must be present; to test the standard input, use
                “-” as a filename argument.

        -i      Causes the file command to output mime type
                strings rather than the more traditional human
                readable ones. Thus it may say “text/plain;
                charset=us-ascii” rather than “ASCII text”. In
                order for this option to work, file changes the
                way it handles files recognised by the command
                it’s self (such as many of the text file types,
                directories etc), and makes use of an alternative
                “magic” file. (See “FILES” section, below).

-k Don’t stop at the first match, keep going.

        -m list
Specify an alternate list of files containing
                magic numbers.   This can be a single file, or a
                colon-separated list of files.

        -n      Force stdout to be flushed after check a file.
                This is only useful if checking a list of files.
                It is intended to be used by programs want filetype
output from a pipe.

-v Print the version of the program and exit.

-z Try to look inside compressed files.

-L option causes symlinks to be followed, as the
like-named option in ls(1). (on systems that support
symbolic links).

        -s      Normally, file only attempts to read and determine
                the type of argument files which stat(2) reports
                are   ordinary files.   This prevents problems,
                because reading special files may have peculiar
                consequences.   Specifying the -s option causes
                file to also read argument files which are block
                or character special files. This is useful for
                determining the filesystem types of the data in
                raw disk partitions, which are block special
                files. This option also causes file to disregard
                the file size as reported by stat(2) since on some
                systems it reports a zero size for raw disk partitions.

Here’s a very simple usage example:
file /bin/sh
file script.sh

For more info do: man file

——————————————————————————-

find
find is a very powerful and useful command, it is as good for finding
a file name as to helping you secure your system against hackers.

find works basicly like this: find <path> [argument] <file>

You REALLY need to read it’s manual page, if you wanna know
about this command, but here are some examples:

Find all files that are set suid root:
find / -perm +4000

Find all regular files named core (this will skip directory’s):
find / -type f -name core

Find all filenames that contains the word ‘conf’:
find / -name *conf*

Find all directory’s that ends with ‘bin’:
find / -type d -name *bin

Find all files named test.sh and execute them:
find / -name test.sh -exec {} \;

Find all regular files that contains the word .exe and
remove them by force without asking:
find / -type f -name *.exe -exec rm {} -rf \;

Even if you are root you may come across errors like this:

find: /proc/10502/fd: Permission denied

The easiest way to deal with this is to add a: 2>/dev/null
after your command string, that will direct all such errors
to /dev/null (the black hole of UNIX :P)

——————————————————————————-

ftpwho
ftpwho is a command where you can see how many users there are
logged on to your ftp, under the condition that you have an
ftp server on your system that is.

——————————————————————————-

g++
GNU C++ compiler.
See it’s man page.
——————————————————————————-

gcc
GNU C Compiler.
See cc
And see the gcc man page

——————————————————————————-

gdb
GNU Debugger, has ALOT of commands and arguments,
see: man gdb.

——————————————————————————-

gpm
gpm is the Linux mouse daemon, it’s unspareble when it comes to
working an a console, cut & paste is a wonderful thing.
gpm works basicly as this: gpm [options]
The most common options would be as this:

gpm -m /dev/mouse -t ps2

This would start a PS/2 mouse, under the conditions that the
PS/2 port (/dev/psaux) is linked to the mouse device (/dev/mouse).

You can use “gpm -m /dev/psaux -t ps2” just as well.
Or if you have a serial mouse no COM1 you can start it like this:

gpm -m /dev/cua0 -t ms

The -m argument means, the mouse device, and the -t argument is
the protocol it’s going to use.

For a list of all gpm’s arguments do: gpm -h
And for a list of all the possible mouse protocols, do: gpm -t help

The basic console cut & paste functions for a 3 button mouser is:

Left button – hold and drag to highlight text (copy’s text to memory).

Middle button – pastes text that are in memory (see left button)

Right button – mark a starting point with a single left click and then
mark an end point with the right button to highlight the whole section.

Once you get it to work, you may add the line to: /etc/rc.d/rc.local

——————————————————————————-

grep
grep is another of the very powerful commands

——————————————————————————-

halt
This will halt (shutdown -h now) your system.

——————————————————————————-

hdparm
hdparm is a powerful tool to control your hard drives.
It works like this: hdparm <arguments> <hard drive>
The arguments can be:

-a   get/set fs readahead
-A   set drive read-lookahead flag (0/1)
-c   get/set IDE 32-bit IO setting
-C   check IDE power mode status
-d   get/set using_dma flag
-D   enable/disable drive defect-mgmt
-E   set cd-rom drive speed
-f   flush buffer cache for device on exit
-g   display drive geometry
-h   display terse usage information
-i   display drive identification
-I   read drive identification directly from drive
-k   get/set keep_settings_over_reset flag (0/1)
-K   set drive keep_features_over_reset flag (0/1)
-L   set drive doorlock (0/1) (removable harddisks only)
-m   get/set multiple sector count
-n   get/set ignore-write-errors flag (0/1)
-p   set PIO mode on IDE interface chipset (0,1,2,3,4,…)
-P   set drive prefetch count
-q   change next setting quietly
-r   get/set readonly flag (DANGEROUS to set)
-R   register an IDE interface (DANGEROUS)
-S   set standby (spindown) timeout
-t   perform device read timings
-T   perform cache read timings
-u   get/set unmaskirq flag (0/1)
-U   un-register an IDE interface (DANGEROUS)
-v   default; same as -acdgkmnru (-gr for SCSI, -adgr for XT)
-V   display program version and exit immediately
-W   set drive write-caching flag (0/1) (DANGEROUS)
-X   set IDE xfer mode (DANGEROUS)
-y   put IDE drive in standby mode
-Y   put IDE drive to sleep
-Z   disable Seagate auto-powersaving mode

Some examples:
hdparm -Tt /dev/hda (Time the cache/device read times)
hdparm -c 1 /dev/hda (This made my HD read the cache twice as fast)
hdparm -Yy /dev/hda (This will totally power down the HD until
it’s needed, very useful to save power
or if you just need a minutes silence)

For more info: man hdparm

——————————————————————————-

head
the head command by default brings up the 10 top lines of a file,
but can be used with these arguments:

-<n>    where the <n> is the number of lines to get
   -c, –bytes=SIZE         print first SIZE bytes
   -n, –lines=NUMBER       print first NUMBER lines instead of first 10
   -q, –quiet, –silent    never print headers giving file names
   -v, –verbose            always print headers giving file names
           –help               display this help and exit
          –version            output version information and exit

Here’s some examples:

head file

head -1 file

head -50 file

head -c 100 file

This command can prove to be very useful.

——————————————————————————-

help
help is a command that shows information on built in commands.
like ., cd, jobs, %, test, etc.
It works like this: help <command>

——————————————————————————-

hexdump
hexdump is a command that will give a hex dump of any file.
For more info on this command do: man hexdump

——————————————————————————-

hexedit
hexedit is a hex editor, very good for debugging binarys,
hexedit has alot of internal commands, do: man hexedit
for more help on it.

——————————————————————————-

hostname
With no arguments it displays the current hostname.
But can also set a new hostname, here are it’s arguments:

     -s, –short           short host name
     -a, –alias           alias names
     -i, –ip-address      addresses for the hostname
     -f, –fqdn, –long    long host name (FQDN)
     -d, –domain          DNS domain name
     -y, –yp, –nis       NIS/YP domainname
     -F, –file            read hostname or NIS domainname from given file

Here’s an example if you wanna change your hostname:

hostname -F /etc/HOSTNAME

——————————————————————————-

id
Shows you a users ID, default your user UID, GID and group name.
The command has some arguments it can be used with, like this:

id [argument] <user>

Here are the arguments:

   -a              ignore, for compatibility with other versions
   -g, –group     print only the group ID
   -G, –groups    print only the supplementary groups
   -n, –name      print a name instead of a number, for -ugG
   -r, –real      print the real ID instead of effective ID, for -ugG
   -u, –user      print only the user ID
       –help      display this help and exit
       –version   output version information and exit

So `id -u` will return ‘0’ if you are root (same as `echo $UID`).

——————————————————————————-

ifdown
ifdown is a command that will let you shutdown (deactivate) any
ethernet device. I works as this: ifdown <device>
So say that you have an eth0 running that you wanna shut down, then
you just do this: ifdown eth0

For more info on how to set up an ethernet device,
see section 7 (Networking) in this tutorial.

——————————————————————————-

ifup
ifup works the same as ifdown, but activates the ethernet device
rather then deactivate it.

For more info on how to set up an ethernet device,
see section 7 (Networking) in this tutorial.

——————————————————————————-

init
init sets the runlevel for you.
If you have read the whole of this tutorial to this point you know
about where to look for what they mean.
So if you do: init 0
The system will shutdown and halt there.
And if you type: init 6
The system will reboot, etc.

——————————————————————————-

insmod
insmod tries to installs a loadable module in the running kernel.
It works like this:

insmod [arguments] <-o module_name> object_file [ sym-bol=value … ]

Here are the possible arguments:
   -f, –force         Force loading under wrong kernel version
   -k, –autoclean     Make module autoclean-able
   -m                  Generate load map (so crashes can be traced)
   -o NAME
       –name=NAME     Set internal module name to NAME
   -p, –poll          Poll mode; check if the module matches the kernel
   -s, –syslog        Report errors via syslog
   -v, –verbose       Verbose output
   -V, –version       Show version
   -x                  Do not export externs
   -X                  Do export externs (default)

An example of how to use this is:

insmod -o 3c90x /lib/modules/2.2.14/net/3c90x.o

This would load the 3c90x.o module with 3c90x as name.

——————————————————————————-

install
install is a command that installs a file properly,
it works like this: install [arguments] source destination
The arguments can be any of the following:

-b, –backup
make backup before removal

-c
(ignored)

-d, –directory
treat all arguments as directory names; create all
components of the specified directories

-D
create all leading components of DEST except the last,
then copy SOURCE to DEST; useful in the 1st format

-g, –group=GROUP
set group ownership, instead of process’ current group

-m, –mode=MODE
set permission mode (as in chmod), instead of rwxr-xr-x

-o, –owner=OWNER
set ownership (super-user only)

-p, –preserve-timestamps
apply access/modification times of SOURCE files to
corresponding destination files

-s, –strip
strip symbol tables, only for 1st and 2nd formats

-S, –suffix=SUFFIX
override the usual backup suffix

–verbose
print the name of each directory as it is created

-V, –version-control=WORD
override the usual version control

–help
display the help and exit

So if we have a file called foo and we want to install it in
/usr/local/bin/, and we want it to have the following permission line:
-rwxr-x—, then we want it to belong to the group ftp, then
we do like this:

install -m 750 foo -g ftp /usr/local/bin/

We could also use:

install -m u+rwx,g+rx foo -g ftp /usr/local/bin/

Which would produce the same permission line.

The install command is good to use if you ever do anything that
needs to be installed to the system, in a proper way.

——————————————————————————-

ipchains
ipchains is a firewall/wrapper that has ALOT of argument,
it’s one of those huge commands, do: man ipchains
for more information on this command.

——————————————————————————-

ispell
Interactive Spell check, this is a useful little command,
it’s basic usage is: ispell <file>
It has the following commands:

R       Replace the misspelled word completely.
Space   Accept the word this time only.
A       Accept the word for the rest of this session.
I       Accept the word, and put it in your private dictionary.
U       Accept and add lowercase version to private dictionary.
0-n     Replace with one of the suggested words.
L       Look up words in system dictionary.
X       Write the rest of this file, ignoring misspellings,
                and start next file.
Q       Quit immediately. Asks for confirmation.
                Leaves file unchanged.
!       Shell escape.
^L      Redraw screen.
^Z      Suspend program.
?       Show the help screen.

Just run it on a file and test it for your self.

——————————————————————————-

kill
kill is a very powerful command that can (if you’re root)
kill any running process no the system.
it works as: kill -<signal> <PID>

Pid is short for Process ID, which you get with the `ps` command.

The signals can be any of the following:

POSIX signals:

        Signal     Value     Action   Comment
        ———————————————————————-
        SIGHUP        1        A     Hangup detected on controlling terminal
                                     or death of controlling process
        SIGINT        2        A     Interrupt from keyboard
        SIGQUIT       3        C     Quit from keyboard
        SIGILL        4        C     Illegal Instruction
        SIGABRT       6        C     Abort signal from abort(3)
        SIGFPE        8        C     Floating point exception
        SIGKILL       9       AEF    Kill signal
        SIGSEGV      11        C     Invalid memory reference
        SIGPIPE      13        A     Broken pipe: write to pipe with no readers
        SIGALRM      14        A     Timer signal from alarm(2)
        SIGTERM      15        A     Termination signal
        SIGUSR1   30,10,16     A     User-defined signal 1
        SIGUSR2   31,12,17     A     User-defined signal 2
        SIGCHLD   20,17,18     B     Child stopped or terminated
        SIGCONT   19,18,25           Continue if stopped
        SIGSTOP   17,19,23    DEF    Stop process
        SIGTSTP   18,20,24     D     Stop typed at tty
        SIGTTIN   21,21,26     D     tty input for background process
        SIGTTOU   22,22,27     D     tty output for background process

Non-POSIX signals:

        Signal       Value     Action   Comment
        ———————————————————————-
        SIGBUS      10,7,10      C     Bus error (bad memory access)
        SIGPOLL                  A     Pollable event (Sys V). Synonym of SIGIO
        SIGPROF     27,27,29     A     Profiling timer expired
        SIGSYS      12,-,12      C     Bad argument to routine (SVID)
        SIGTRAP        5         C     Trace/breakpoint trap
        SIGURG      16,23,21     B     Urgent condition on socket (4.2 BSD)
        SIGVTALRM   26,26,28     A     Virtual alarm clock (4.2 BSD)
        SIGXCPU     24,24,30     C     CPU time limit exceeded (4.2 BSD)
        SIGXFSZ     25,25,31     C     File size limit exceeded (4.2 BSD)

Other signals:

        Signal       Value     Action   Comment
        ——————————————————————-
        SIGIOT         6         C     IOT trap. A synonym for SIGABRT
        SIGEMT       7,-,7
        SIGSTKFLT    -,16,-      A     Stack fault on coprocessor
        SIGIO       23,29,22     A     I/O now possible (4.2 BSD)
        SIGCLD       -,-,18            A synonym for SIGCHLD
        SIGPWR      29,30,19     A     Power failure (System V)
        SIGINFO      29,-,-            A synonym for SIGPWR
        SIGLOST      -,-,-       A     File lock lost
        SIGWINCH    28,28,20     B     Window resize signal (4.3 BSD, Sun)
        SIGUNUSED    -,31,-      A     Unused signal (will be SIGSYS)

When you use the kill you can either use the numeric code, as
say that we have a PID 1234 that we wanna kill, then we can either
do: kill -9 1234 or we can do: kill -KILL 1234
So you don’t have to include that leading SIG in the signals
when you use them by name.

——————————————————————————-

killall
killall is the same as kill but kills processes by name,
As say that you have 10 processes running all named: httpd
and you wanna kill them all in one command.
Then: killall -9 httpd would be the way to go about it.

——————————————————————————-

lastlog
lastlog is a command that shows you a list of the users and when
they last logged in, from what host and on which port.
lastlog can be used with the following arguments:

-u username
-t number of days

so if I wanna check if a user named ‘user’ has logged in during
the last 50 days I do: lastlog -u user -t 50

——————————————————————————-

ldconfig
ldconfig updates the list of directory’s in where library’s can be
found as /lib and /usr/lib, if you wanna add a directory to this you
can add them in /etc/ld.so.conf
By just typing `ldconfig` you will update this, but it can
also be executed with more arguments, for more info on this
command do: man ldconfig

Just note that this is not really a command that you will use
every day.

——————————————————————————-

ldd
ldd can check what librarys a dynamicly executable file needs.
and it can have the following switches:

       –help                  print this help and exit
       –version               print version information and exit
   -d, –data-relocs       process data relocations
   -r, –function-relocs   process data and function relocations
   -v, –verbose           print all information

It works like this:

ldd <file>

Example:

ldd /sbin/ifconfig

——————————————————————————-

less
less is more then more ….. ummmm
less works a bit like cat but it will stop at each screen and you
can scroll up and down in the file to view it’s contents,
it works basicly like this: less <textfile>
Do a: less –help
For a full index of it’s commands, and note that you get out
of less by pressing the letter ‘q’.

——————————————————————————-

lilo
lilo is the LInux LOader, and is on most distros the default
boot loader, with lilo you can rewrite your boot sector and
everything that involves your booting or switching between
several installed operating systems, lilo’s configuration file
is /etc/lilo.conf
for more info about lilo and what lilo can do do: man lilo

——————————————————————————-

ln
link, with ln you can link any file, this is essential to *nix
as, say that you have a config file that needs to be in the same
dir as it’s program but you want it in /etc with all the other
configuration files, then you can link it to /etc so the link
appears in /etc and works just like the real file.

Usually ln is used to set symbolic links (sym links) where you
can see the difference of the link and the file and you can remove
the link without it affecting the real file.
A symbolic link is set in this way: ln -s file link

——————————————————————————-

lndir
link directory, about the same as ln but links directory’s,
see the: man lndir

——————————————————————————-

loadkeys
loadkeys, basicly works like: loadkeys /usr/lib/kbd/keymaps/<keymap>
but also has some arguments (that I never used), if you want
more info: man loadkeys

——————————————————————————-

locate
locate can locate any file that’s read into a database,
you update this database if you as root type: updatedb
locate works basicly like: locate <whatever-you-wanna-find>
but can be executed with alot of arguments, do: locate –help
or for more info: man locate

——————————————————————————-

logout
logout does what it says, it logs you off the shell.

——————————————————————————-

lpq
line printer que, checks if you have any printer jobs on que.

——————————————————————————-

lpr
line printer, has alot of commands, but basicly works as: lpr <file>
to print a file, the lpr command has alot of arguments,
do: man lpr for more info.

——————————————————————————-

lprm
line printer remove, removes any qued jobs (lpq) by there entry number.

——————————————————————————-

ls
this is the most basic of all basic commands to know.
ls lists the contents of a directory, if you type just `ls`
it will list the contents of the current directory, but it can also
be used as `ls /way/to/some/other/dir/` to list the contents of
some other directory, ls has alot of arguments which are:

-a, –all
do not hide entries starting with .

-A, –almost-all
do not list implied . and ..

-b, –escape
print octal escapes for nongraphic characters

–block-size=SIZE
use SIZE-byte blocks

-B, –ignore-backups
do not list implied entries ending with ~

-c
sort by change time; with -l: show ctime

-C
list entries by columns

–color[=WHEN]
control whether color is used to distinguish file
types. WHEN may be `never’, `always’, or `auto’

-d, –directory
list directory entries instead of contents

-D, –dired
generate output designed for Emacs’ dired mode

-f
do not sort, enable -aU, disable -lst

-F, –classify
append indicator (one of */=@|) to entries

–format=WORD
across -x, commas -m, horizontal -x, long -l,
single-column -1, verbose -l, vertical -C

–full-time
list both full date and full time

-g
(ignored)

-G, –no-group
inhibit display of group information

-h, –human-readable
print sizes in human readable format (e.g., 1K 234M 2G)

-H, –si
likewise, but use powers of 1000 not 1024

–indicator-style=WORD
append indicator with style WORD to entry names:
none (default), classify (-F), file-type (-p)

-i, –inode
print index number of each file

-I, –ignore=PATTERN
do not list implied entries matching shell PATTERN

-k, –kilobytes
like –block-size=1024

-l
use a long listing format

-L, –dereference
list entries pointed to by symbolic links

-m
fill width with a comma separated list of entries

-n, –numeric-uid-gid
list numeric UIDs and GIDs instead of names

-N, –literal
print raw entry names (don’t treat e.g. control
characters specially)

-o
use long listing format without group info

-p, –file-type
append indicator (one of /=@|) to entries

-q, –hide-control-chars
print ? instead of non graphic characters

–show-control-chars
show non graphic characters as-is (default)

-Q, –quote-name
enclose entry names in double quotes

–quoting-style=WORD
use quoting style WORD for entry names:
literal, shell, shell-always, c, escape

-r, –reverse
reverse order while sorting

-R, –recursive
list subdirectories recursively

-s, –size
print size of each file, in blocks

-S
sort by file size

–sort=WORD
extension -X, none -U, size -S, time -t, version -v
status -c, time -t, atime -u, access -u, use -u

    –time=WORD
show time as WORD instead of modification time:
                atime, access, use, ctime or status; use
                specified time as sort key if –sort=time

-t
sort by modification time

-T, –tabsize=COLS
assume tab stops at each COLS instead of 8

-u
sort by last access time; with -l: show atime

-U
do not sort; list entries in directory order

-v
sort by version

-w, –width=COLS
assume screen width instead of current value

-x
list entries by lines instead of by columns

-X
sort alphabetically by entry extension

-1
list one file per line

–help display this help and exit
–version output version information and exit

Some good examples are:

ls -la
ls -laF
ls -laF –color
ls -d */

Also see earlier in this tutorial about the `alias` command

——————————————————————————-

lsattr
list attributes, this command lists a files file system attributes.
For more info see: man lsattr

——————————————————————————-

lsmod
list modules, lists all loaded modules with a very brief information.

——————————————————————————-

lsof
list open files, this is a huge command, so if you really
wanna find out more about this interesting command you will have
to read the manual page for it.
But here’s an example of use for it:

lsof -p 1

Which would be the same as:

lsof -p `pidof init`

Here’s another example:

lsof -p `pidof httpd | sed ‘s/\ /,/g’`

The “-p” means that the following argument will be a PID (Process ID).
The “sed” part in the later example replaces any spaces with “,” since
lsof doesnt want spaces between the pids, as the output of pidof gives.

For more info see: man lsof

——————————————————————————-

lynx
lynx is a console based world wide web browser, that has alot of
arguments with which it can be executed, but it basicly works like
this: lynx <url>
If you press ‘g’ while in lynx you can type in the url where you
wanna go, and if you press ‘q’ you quit lynx.
You search in text with lynx with ‘/’ and move around with
the arrow keys and the TAB key.

A tips is that lynx works as a file manager, as this: lynx </path/>

A good usage for lynx is that you can use it as direct downloader,
like this: lynx -souce ftp://ftp.bogus.com/foo/bar.tar.gz > bar.tar.gz

For more help or information do: lynx –help
Or: man lynx

——————————————————————————-

mail
mail is most commonly used to just check your mail in the most
simple way by just typing `mail`, but it can also be used
with alot of arguments, I have personally never used
any arguments to the mail command, but if you wanna check
them out do: man mail

——————————————————————————-

man
manual pages, there are several different manual pages, say for example
the command exec, `man exec` should bring you little, while
`man 3 exec` should bring you the C function manual on exec.

The man pages traditional way of storing is:

man1 misc user commands
man2 C programming functions
man3 more C programming functions
man4 network related manuals
man5 system related files
man6 game manuals
man7 misc technical manuals
man8 misc superuser commands
man9 misc system/devices

I may be wrong about the category’s there, but that’s how it seems
to me.
Anyway, to bring up a manual page simply do: man <command>
or: man <number> <command>

——————————————————————————-

mc
midnight commander is a visual shell for *nix Operating Systems.
mc is quite large and has alot of arguments, I personally don’t use
midnight commander at all, but if you wanna learn more about it
do: man mc

——————————————————————————-

mesg
mesg is a command with which you control if other users should
have write access to your terminal, as `wall` messages, `write`
or anything similar.

mesg y turns on the access for others to write to your terminal.
mesg n turns off the access for others to write to your terminal.

——————————————————————————-

mkdir
make directory, creates a directory, works as: mkdir [arguments] dir/
The arguments can be as follows:

-m, –mode=MODE see chmod’s octal (numerical) modes

-p, –parents no error if existing, make parent
directories as needed

–verbose print a message for each created directory

–help display the help and exit

–version output version information and exit

mkdir is most commonly used as: mkdir <newdir>

——————————————————————————-

mknod
mknod is used to create special files, as devices.
mknod’s syntax is this: mknod [arguments] <name> <type> [MAJOR MINOR]
It can be used with the following arguments:

-m, –mode=MODE
set permission mode (as in chmod), not 0666 – umask

–help
display this help and exit

–version
output version information and exit

MAJOR MINOR are forbidden for <type> p, else they must be used.

b create a block (buffered) special file

c, u create a character (unbuffered) special file

p create a FIFO

You need to know the devices major/minior number if you gonna use this
command, those are located in /usr/src/linux/Documentation/devices.txt
that comes with the kenrnel source.
The “char” is the minior and the number before the devices are the
major numbers so say that you wanna make a new /dev/null for some
reason, then you read the devices.txt and see this:

        1 char        Memory devices
                    1 = /dev/mem          Physical memory access
                 2 = /dev/kmem         Kernel virtual memory access
                        3 = /dev/null         Null device

And so you make the null device like this:

mknod /dev/null b 1 3

Or if you wanna make a new /dev/scd device to support another
emulated scsi cdrom device. (there are 7 scd devices default)
So here’s how you make another:

mknod /dev/scd8 b 11 8

This is not as hard at all …..

for more info: info mknod
or: man mknod

——————————————————————————-

modprobe
modprobe loads modules in a similar way as depmod.
See modprobe’s manual page: man modprobe

——————————————————————————-

more
more is a command to display a files contents, it’s very similar
to the `less` command.
See `less` and more’s manual pages: man more

——————————————————————————-

mount
mount, mounts a media, that is to say that you make the contents
of say a hard drive visible to the system on some mountpoint,
ie. mount -t vfat /dev/hda1 /windows
This command would mount hda1 (the first harddrive’s (hd a)
first partition (hda 1), as (-t <filesystem>) vfat which is
the windows native filesystem.
Linux native filesystem is ext2.

mount has ALOT of arguments, if you wanna read about them all
do: man mount

——————————————————————————-

mv
mv, moves a file or directory.
It works like this: mv [argument] <file-to-move> <new-name/location>
This is an example: mv /home/alien/bash.tutor /home/old/bash.tutor
Or just to rename a file: mv bash.tutor bash.file

mv can also be executed with alot of arguments, which are:

-b, –backup
make backup before removal

-f, –force
remove existing destinations, never prompt

-i, –interactive
prompt before overwrite

-S, –suffix=SUFFIX
override the usual backup suffix

-u, –update
move only older or brand new non-directories

-v, –verbose
explain what is being done

-V, –version-control=WORD
override the usual version control

–help
display the help and exit

–version
output version information and exit

Here’s an example: mv -f /home/alien/bash.tutor /
This will by force mv the file to / (if you have write rights to /)

——————————————————————————-

nc / netcat
netcat is by default usually located in: /usr/lib/linuxconf/lib/
netcat is very useful in internet based shell scripts, since
it can listen on a socket or send to sockets, depending on the version.
the default netcat can as far as I know only send to sockets.
works basicly like this:

/usr/lib/linuxconf/lib/netcat –file <file> <ip> <port>

But can be executed with the following arguments:
–head <nb_lines>
–tail <nb_lines>
–send <file>

A tip is to make one or two links from /usr/lib/linuxconf/lib/netcat
to /usr/local/bin/netcat and perhaps /usr/local/bin/nc

——————————————————————————-

ncftp
ncftp is a very powerful ftp client.
ncftp has the following syntax: ncftp [arguments] <host>
If no arguments is given it will try to login as anonymous user
with an e-mail as password.

Most common non-anonymous usage is this: ncftp -u <username> <host>

The commands you will use the most once logged on to an ftp
is the following:

get <name> download a file
put <name> upload a file
ls list current directory
cd <dir-name> change directory
lls list local directory
lcd change local directory

If you want to read all ncftp’s commands and arguments do: man ncftp

——————————————————————————-

ncftpget
ncftpget is a command line based ftp download client. It works
like this: ncftpget [arguments] <host> <local-dir> <remote-files>

ncftpget comes with ncftp, if you want to see all it’s commands,
do: man ncftpget

——————————————————————————-

ncftpput
ncftpput is a command line based ftp upload client. It works
like this: ncftpput [arguments] <host> <remote-dir> <remote-files>

ncftpput comes with ncftp, if you want to see all it’s commands,
do: man ncftpput

——————————————————————————-

netstat
netstat will show you the network connections to and from your computer
that’s currently active, it can simply be used by typing `netcat`
or it can me used with it’s arguments, if you wanna learn
more about this command, do: man netcat

——————————————————————————-

nice
nice is a command that can set the priority (cpu time) of a program
or a command, the prioretys can be from -20 which is max priority
to 19 which is the minimum priority.
nice works like this: nice [argument] <command> <argument>
The arguments “[argument]” for nice can be:

-ADJUST
increment priority by ADJUST first

-n, –adjustment=ADJUST
same as -ADJUST

–help
display the help and exit

–version
output version information and exit

Example: nice -n -20 make bzImage
This will make the kernel with as much CPU as it can.
This means this process has more rights then any other process.

Another example is: nice -n 19 zgv
This will give zgv absolutely lowest priority, and will there for
be the slowest moving processes on the system, as if it runs
with nice 19 and another process comes and wants more CPU power
then there is free, `zgv` will in this case give the other
process of it’s own power.

——————————————————————————-

nmap
nmap is getting to come as default for some Linux distributions,
and is a port scanner, maybe the best port scanner there is.

nmap is used like this: nmap [arguments] <host / ip>
So say you want to port scan yourself you could do:
nmap 127.0.0.1
Or: nmap localhost
The most commonly used arguments to nmap is the ‘-sS’ which
is a SYN scan, and will in most cases not reveal your IP
to the one that your scanning, BUT if the other side
has any kind of modern logging device as a fairly new
firewall or port logger your IP will be shown to him anyway.

The other perhaps next most common argument to use is the ‘-O’
argument, which will give you a good guess of what the remote
operating system is this function works the same as for
the operating system guess program `queso`.

Example: nmap -sS -O localhost > localhost.log

The ‘> localhost.log’ part will put the outcome of the scan in a file
called localhost.log.

——————————————————————————-

ntpdate
ntpdate has no manual page nor any help page what I can found,
perhaps I’ll write one if I’m bored some day …..

ntpdate will synchronize your computers system clock with an atomic
clock.

ntpdate’s help usage gives this:

usage: ntpdate [-bBdqsv] [-a key#] [-e delay] [-k file] [-p samples]
[-o version#] [-r rate] [-t timeo] server …

I only use it as: ntpdate <server>
Like this: ntpdate ntp.lth.se

——————————————————————————-

ntsys / ntsysv
runlevel confuration tool.
This tool lets you configure what services that should be
started with your runlevel, alteast ntsysv has a nice
ncurses interface that’s easy to handle.

For moreinformation on this command do: man ntsys
Or: man ntsysv
Depending on your system.

——————————————————————————-

objdump
objdump is a quite large command, that allows you to dump objects
out of a binary file.
To dump all objects do: objdump –source <binary file>
For more info do: man objdump

——————————————————————————-

passwd
passwd is a little tool to set a password to a user account,
it basicly works like this: passwd [arguments] <username>
or if you just type `passwd` you will change your own password.
passwd can be sued with the following arguments:

-d, –delete        delete the password for the named account
       (root only)
   -f, –force         force operation
   -k, –keep-tokens   keep non-expired authentication tokens
   -l, –lock          lock the named account (root only)
   -S, –status        report password status on the named account
       (root only)
       –stdin         read new tokens from stdin (root only)
   -u, –unlock        unlock the named account (root only)

Help options

-?, –help Show the help message
–usage Display brief usage message

You still need to do a: man passwd

——————————————————————————-

patch
patch simply works like this: patch <original-file> <patch-file>
A patch is done with the `diff` command as
this: diff file1 file2 > patchfile
So then to make file1 identical to file2: patch file1 patchfile

patch can however be used with a whole lot of arguments,
if you are interested do: man patch
Or: patch –help

——————————————————————————-

pidof
pidof simply gives the PID of a running process without you having
to use “ps”, say that you want to find out what pid your init has,
(it will always be one for the init), then you do: pidof init
Or if you wanna find out which pids are used by the web server (httpd)
then you do: pidof httpd
So basically you find out the pids from the process name(s).

pidof has the following switches:

-s Single shot – this instructs the program to only return one pid.

-x Scripts too – this causes the program to also return process
id’s of shells running the named scripts.

        -o     Tells pidof to omit processes with that process id.
               The special pid %PPID can be used to name the parent process of
               the pidof program, in other words the calling shell or shell
               script.

For more info see: man pidof

——————————————————————————-

ping
ping is a pretty basic command, that will work
as: ping [arguments] <ip-or-host>
The arguments can be as follows:

-c <number> count pings to send
-d debug
-f ping flood
-i <number> wait number of seconds between each ping
-l <number> preload number of pings
-n numeric IP’s only
-p pattern (in hex) to send as pad code in the ping header
-q quiet
-R record route
-s <number> packet size in bytes
-v Verbose output

So say that you wanna send 5 pings that’s 128 bytes each to
IP 127.0.0.1, then you would do: ping -s 128 -c 5 127.0.0.1

——————————————————————————-

pmake
pmake is *BSD make (so I’m told), see make and: man pmake

——————————————————————————-

pnpdump
pnpdump gives a dump of all ISA pnp devices, good to use
with isapnp etc.
This is the command you wanna have a look at if your either
looking for exact info of some ISA device that is pnp, or
if your system has problems finding a ISA pnp device.
See the manual pages.

——————————————————————————-

portmap
portmap is the server that maps all RPC services, so if you
wanna use any RPC service you wanna have portmap running.
For more info: man portmap

——————————————————————————-

ps
ps gives you the process list, as in showing you the running
processes with there pid and other info.
do: ps –help
or: man ps for more info on what arguments it can be executed
with, personally I use: `ps aux` and `ps x` the most.

——————————————————————————-

pstree
process tree, a bit more (ascii) graphical version of ps,
do: pstree –help
or: man pstree
for more help on the arguments, personally I use it alone without
arguments.

——————————————————————————-

pwd
print working directory, shows you your current directory.
This command can be useful for 2 things what I know of,
one is to show you where you are, and the other in scripts
to do say: echo “output will go to: `pwd`/logfile”

——————————————————————————-

quota
quota prints the users quota, it works like
this: quota [arguments] <user/group>
Where the arguments can be:

-g Print group quotas for the group of which the user
is a member. The optional

-u flag is equivalent to the default.

-v will display quotas on filesystems where no storage
is allocated.

-q Print a more terse message, containing only infor-
mation on filesystems where usage is over quota.

For more info on the quota command do: man quota

——————————————————————————-

quotaoff
quotaoff turns the quota off for a file system.
quotaoff works like this: quotaoff [arguments] <filesystem>
The arguments can be as follows:

-a Force all file systems in /etc/fstab to have their
quotas disabled.

-v Display a message for each file system affected.

-u Manipulate user quotas. This is the default.

-g Manipulate group quotas.

This command is close to quotaon.

For more info: man quotaon
(Don’t think there is a quotaoff man page, quotaon and quotaoff
seems to have the same manual page)

——————————————————————————-

quotaon
        quotaon turns the quota on for a file system.
        quotaon works like this: quotaon [arguments] <filesystem>
        The arguments can be as follows:

-a      All file systems in /etc/fstab marked read-write
               with quotas will have their quotas turned on. This
               is normally used at boot time to enable quotas.

-v Display a message for each file system where quotas
are turned on.

-u Manipulate user quotas. This is the default.

-g Manipulate group quotas.

For more info: man quotaon

——————————————————————————-

quotastats
quotastats displays the quota stats …. cant find any help, –help
or manual page for it.

——————————————————————————-

read
read, reads a variable.

Example:

echo -n “password: ”
read pass
echo “Password was: $pass”

For more info: help read

——————————————————————————-

reboot
reboot does what it says, it reboots the system, you have to be root
to use this command.
reboot works the same as: shutdown -r now
or also the same as if you press: Ctrl+Alt+Del
Nothing much more to say about the reboot command.

——————————————————————————-

reset
reset resets the console, say that you have accidently done
cat <binary-file> so you totally screwed up your console
and you cant read anything on it, then just type `reset`
and press enter, and it should be back to normal within some seconds.

——————————————————————————-

rlogin
remote login, if you wanna use this command do: man rlogin
bore using it.
The most common use of it is: rlogin -l <username> <host>

——————————————————————————-

rm
remove, remove/unlink files, rm can be used with the
following arguments:

   -d, –directory       unlink directory, even if non-empty
         (super-user only)
   -f, –force           ignore nonexistent files, never prompt
   -i, –interactive     prompt before any removal
   -r, -R, –recursive   remove the contents of directories recursively
   -v, –verbose         explain what is being done
           –help            display this help and exit
           –version         output version information and exit

An example is, that if you have a directory called /foo
that you wanna delete recursively, then you do: rm -rf /foo
Or say that you have a file /foo/bar that you wanna remove
without being prompted, then you do it like this: rm -f /foo/bar
——————————————————————————-

rmmod
        remove modules, remove a loaded module.
        List the modules that you can remove with lsmod.
        And load modules with insmod.
        man any of them for more information.

——————————————————————————-

route
route, displays the routing table by default.
The most common way of adding a route is like this:
route add -host <ip> gw <other-ip>

And to remove a post:
route del -host <ip> gw <other-ip>

An example would be, say that you want to route IP 123.123.123.123
to 127.0.0.1, this would drop any connection attempts from
123.123.123.123 to 127.0.0.1 so he cant connect to you or scan you,
(this is true in most cases), you would do:

route add -host 123.123.123.123 gw 127.0.0.1

Now the route command is bigger then that, so if you wanna
learn more about it do: man route

——————————————————————————-

rpm
rpm is a command that is is very important to most distributions.
rpm is short for ‘redhat package manager’ and was developed for
RedHat by Caldera.
rpm is a HUGE command, and works like this: rpm [arguments] <file>
but here are the most commonly used arguments:

rpm -ivh <package.rpm> installs package.rpm
rpm -Uvh <package.rpm> updates package.rpm
rpm -e <package> un-installed/erases package
rpm -qf <file> displays what package the file came with
rpm -qlp <package.rpm> displays the contents of the package.rpm
rpm -qRp <package.rpm> displays the dependencys needed by package.rpm

Other arguments and that are commonly used but not recommended are:

–force force install something
–nodeps do not check dependences

Another thing is if you installed a *.src.rpm file (that ends up in
/usr/src/RPM/*), you can compile a binary .rpm from it.
Say that you installed some-package.src.rpm, then you would go to:
/usr/src/RPM/SPECS/, and there type: rpm -ba some-package.spec
wait a while during the compile, and then you would have a
/usr/src/RPM/RPMS/<platform>/some-package.<platform>.rpm

the “<platform>” is your platform, as i386, i486, i586, i686,
k6, ppc, sprac, noarch etc.

To create an rpm from a .src.rpm you first need to know that
this should not be done as root for the simple reason that
if you make an rpm as root several unworking parts of it may
remain in your system generating errors if the compile of
the rpm isnt successful.

So the first thing you do to do this as user is to create a file
named .rpmmacros
And in that add the following:
%_topdir ~/RPM

This should work to create the file:
echo “%_topdir $HOME/RPM” > ~/.rpmmacros

Then you do this:
mkdir -p ~/RPM/{SOURCES,SPECS,BUILD,RPMS,SRPMS}

Now you’re ready to start to build an rpm from a .src.rpm
first (as user, not as root) install the source rpm.

rpm -ivh package.src.rpm

Then you go to ~/RPM/SPECS/

The .src.rpm should have installed the sources in ~/RPM/SOURCES
and the spec file in ~/RPM/SPECS/
The spec file is like a script file, it tells rpm how to compile
the source and build the rpm.

Now find the spec file in ~/RPM/SPECS/, it’s usually named the same
as the package, like this:

package.spec

So not to make an rpm out of it, do this:

rpm -ba package.spec

If this is successful (which it sadly enough isnt every time because
of ill written spec files)
You should now have an rpm file in ~/RPM/RPMS/<your architecture>

If you have a Pentium 2, the arch command will show “i586” and
so the rpm will be found in ~/RPM/RPMS/i586/

You will also have a brand new .src.rpm in ~/RPM/SRPMS/

If you need to do the rpm to any other target then your own
architecture, say you want to do it for i386, then you may do:

rpm -ba package.spec –target=i386

And so the new rpm will be found in ~/RPM/RPMS/i386/
This is about all there is to say about the rpm command in this
tutorial.
The rpm command and the spec file *scripting* langauge
would need a rather large tutorial by it self to be explained
in full …. so I wont take up all that here.

For more info on the rpm command do: man rpm

——————————————————————————-

sed
sed, stream editor, is already breafly explained in this tutorial,
so if you want more info do: man sed

——————————————————————————-

setleds
setleds may show or set the flags and lights on NumLock, CapsLock
and ScrollLock.
On it’s own without any arguments it shows the current settings.

The syntax is this: setleds [arguments] <+/-num,caps,scroll>

Here’s the arguments:

        -F This is the default. Only change the VT flags (and
               their setting may be reflected by the keyboard
               leds).

        -D      Change both the VT flags and their default settings
               (so that a subsequent reset will not undo the
               change). This might be useful for people who always
               want to have numlock set.

        -L      Do not touch the VT flags, but only change the
               leds. From this moment on, the leds will no longer
               reflect the VT flags (but display whatever is put
               into them). The command setleds -L (without further
               arguments) will restore the situation in which the
               leds reflect the VT flags.

        -num +num
               Clear or set NumLock.   (At present, the NumLock
               setting influences the interpretation of keypad
               keys.   Pressing the NumLock key complements the
               NumLock setting.)

        -caps +caps
               Clear or set CapsLock. (At present, the CapsLock
               setting complements the Shift key when applied to
               letters. Pressing the CapsLock key complements the
               CapsLock setting.)

        -scroll +scroll
               Clear or set ScrollLock. (At present, pressing the
               ScrollLock key (or ^S/^Q) stops/starts console out-
               put.)

Here is a few example, where the first one is from the manualpage,
(I’d hate to break the cut’n’paste tradition from the manual pages
now), so here are some examples:

       INITTY=/dev/tty[1-8]
              for tty in $INITTY; do
                     setleds -D +num < $tty
              done

This would set numlock on for tty1 to tty8

Here’s another short example:

              while /bin/true; do
      setleds -L +caps; usleep 500000
       setleds -L +num; usleep 500000
      setleds -L -caps; usleep 500000
       setleds -L -num; usleep 500000
       done

This would flash the NumLock and CapsLock leds, for infinety.

For more info do: man setleds

——————————————————————————-

seq
sequence numbers.
seq works baskically like this:

seq [OPTION] LAST
seq [OPTION] FIRST LAST
seq [OPTION] FIRST INCREMENT LAST

And can be used with the following options:

        -f, –format FORMAT      use printf(3) style FORMAT (default: %g)
        -s, –separator STRING   use STRING to separate numbers (default: \n)
        -w, –equal-width        equalize width by padding with leading zeroes
        –help               display this help and exit
        –version            output version information and exit

Here’s some small examples and what they do:

seq 10 (Count from 1 to 10)
seq 5 10 (Count from 5 to 10)
seq 1 2 10 (Count from 1 to 10 by incrementing two: 1,3,5,7,9)
seq 10 0 (Count backwards from 10 to 0)

For more info do: seq –help

——————————————————————————-

sleep
sleep works like this: sleep <number of seconds>
Not much to say about this command, … if you wanna read
more about it: man sleep

——————————————————————————-

sort
sort, sorts the contents of a file and gives the output to stdout.
By default it sorts it in alphabetical order, sort works
like this: sort [arguments] <file>

sort can be executed with the following arguments:

-b ignore leading blanks in sort fields or keys

-c check if given files already sorted, do not sort

-d consider only [a-zA-Z0-9 ] characters in keys

-f fold lower case to upper case characters in keys

-g compare according to general numerical value, imply -b

-i consider only [ 40- 176] characters in keys

        -k POS1[,POS2]
               start a key at POS1, end it *at* POS2
field numbers and character offsets are numbered
               starting with one (contrast with zero-based +POS form)

-m merge already sorted files, do not sort

-M compare (unknown) < `JAN’ < … < `DEC’, imply -b

-n compare according to string numerical value, imply -b

-o FILE
write result on FILE instead of standard output

-r reverse the result of comparisons

-s stabilize sort by disabling last resort comparison

-t SEP use SEParator instead of non- to whitespace transition

-T DIRECTORY
use DIRECTORY for temporary files, not $TMPDIR or /tmp

-u with -c, check for strict ordering; with -m, only
output the first of an equal sequence

-z end lines with 0 byte, not newline, for find -print0

–help display the help and exit

–version output version information and exit

One more time I give thanks to the cut & paste function.

Here’s an example of sort: sort file1 -o sorted-file2
This command works good with the `uniq` command to sort out
duplica words, like this: sort file1 | uniq > sorted-file

For more info do: man sort

——————————————————————————-

ssh
secure shell, works a bit like telnet but has encryption,
ssh is becoming a good standard of encrypted remote shell connections.
ssh is however not usually default included in any distros,
and there is several versions of it, so if you download it
make sure to read all documentations about it.
Even though it’s not default included, I still wanned to include it
in this tutorial to make users that use LAN connections
as local networks with more then one user or cable modems aware
of this tool, because if they use telnet anyone on the local
subnet can sniff the connection and get any login and password
used with incoming or outgoing telnet connections.
Really anyone can sniff anything that’s not encrypted, like
ftp logins and passwords, http, IRC, and everything like that.
but the most vital to protect is the ways people can enter
your system, so if you are on a LAN with more then one user
or have any form of cable or non-dialup connection,
then disable telnet (put a # in front of the telnet line in
/etc/initd.conf and after that do: killall -HUP initd), and then
install ssh.

——————————————————————————-

strip
strip strips binary files (executables) of junk code,
such as debugging information.
This may be very useful to bring down the size of executable files.
BUT beware, if you strip the kernel or any other very complex
binary, they are likely to malfunction, so use this command
wisely, and read it’s manual page.

——————————————————————————-

su
su, the manual pages says substitute user and the UNIX command bible
says super user … so it means any of those, it’s however used
to *become another user*, if you are root and su <user> you wont
need to supply any password.
If you type only `su` as user you will become root if you have the
aproperiet root password.
su can be used with the following arguments:

-, -l, –login               make the shell a login shell
   -c, –commmand=COMMAND       pass a single COMMAND to the shell with -c
   -f, –fast                   pass -f to the shell (for csh or tcsh)
   -m, –preserve-environment   do not reset environment variables
   -p                           same as -m
   -s, –shell=SHELL            run SHELL if /etc/shells allows it
           –help                   display this help and exit
           –version                output version information and exit

Say now that you wanna su to root and have root’s path/enviorment.
then you do: su –
Or say that you wanna execute a single command as root from being
a user, say the command `adduser`, then you do: su -c “adduser”
you will be prompted for the password, and if you can supply it
the command will be executed as root.

——————————————————————————-

swapoff
turns swap off, it can be used with the following arguments:

        -h     Provide help
        -V     Display version
        -s     Display swap usage summary by device. This option
               is only available if /proc/swaps exists (probably
               not before kernel 2.1.25).
        -a     All devices marked as “sw” swap devices in
               /etc/fstab are made available.
-p priority (man swapon and swapoff for more info on prioretys)

Example, say that you wanna turn all swap partitions (from /etc/fstab)
off then you do: swapoff -a
Again, for more info: man swapoff

——————————————————————————-

swapon
swapon is the opposite of swapoff but has the same arguments.
See: man swapon

——————————————————————————-

tail
tail gives by default the last 10 lines out of a file, it’s very alike
the `head` command, ad works like this: tail [arguments] <file>
The most common usage of tail is this:

tail -f <file> This will append the data to stdout as the file grows.
very good to view logs as they come in.

tail -50 <file> Displays the last 50 lines from a file.

tail has more arguments which you can learn in it’s manual page
if you are interested, do: man tail

——————————————————————————-

talk
talk is a little daemon controlled by inetd, so if it doesn’t
work on your local machine make sure the talk line in
/etc/inetd.cond are not remmed by a leading # character.

Talk gives a real time text chat, in a horizontally divided
window or rather console.

Talk works like this: talk user@host
or just user if it’s on the local machine.
Say that I wanna send a talk request to user `alfa` on IP
123.123.123.132, and I’m user `beta` on 234.234.234.234.
Then I type: talk alfa@123.123.123.132
And he as answer when the request comes
types: talk beta@234.234.234.234

What to type as answer comes up when you get a talk request.

For more info on the talk command do: man talk

——————————————————————————-

tar
tar, UNIX tape archive, is yet another huge command,
it’s used to compress a directory to a compressed .tar file,
or a single file to a tar file.
tar works like this: tar [arguments] <directory-or-file>

Here are the most common examples of tar usage:

tar -zvxf <file.tar.gz> uncompress a .tar.gz or .tgz archive
tar -vxf <file.tar> uncompress a .tar archive
tar -c –file=<file.tar> <directory> crates a .tar archive
tar -cf <file.tar> <directory> – same as above –
tar -tf <file.tar> list the contents of a .tar file
tar -tzf <file.tar.gz> list the contents of a .tar.gz or a .tgz file
tar -czvf <file.tar.gz> <directory> crates a .tar.gz archive

For more info on the tar command, do: man tar

——————————————————————————-

tcpdump
tcpdump is a command that let’s you view the traffic on the local
subnet or segment, It’s not default on many Linux distributions.
So if you have it or get it, read it’s documentation and it’s
manual pages, if you want to use it.

——————————————————————————-

telnet
telnet is the most basic of all clients to know.
It’s not often you will ever use it in other ways
then: telnet <host-or-ip> <port>
And it’s not even so often one uses it with the port number after.

Telnet creates a real time connection to another computer,
ofcorse the other computer needs a running telnet daemon,
and you need to have a login and a password to get in.
But when you get in you can remotely work on the other system
just as if you sat in front of it.

Times when it’s good to supply a port number after the host is
most commonly to check the version of some daemon/server,
as if you want to know the version of your own sendmail, you
can always do: telnet 127.0.0.1 25
smtp (send mail transfer protocol) runs on port 25.
If you wonder what port something runs on check in /etc/services

For more info on telnet do: man telnet

——————————————————————————-

test
test is a big command, and is used to generate boolean results
out of 2 arguments, to explain the whole command here would take up
to much space and time, it can be used like this:

test -f /sbin/shutdown && echo “It’s there” || echo “It’s not there”

That line says in clear english:
test if file /sbin/shutdown is there, if outcome is true
echo “It’s there” else echo “It’s not there”.

You can test if a file is executeble, if a string is non-zero etc.
Just about anything you can think of.

For more info on the many things you can do with the `test`
command, do: man test

——————————————————————————-

touch
touch will by default change the date on a file to the current date.
It works like this: touch [arguments] <file>
If the file doesn’t exist if will create a file that’s 0 bytes big.

The following arguments can be used with touch:

-a change only the access time

-c do not create any files

-d, –date=STRING
parse STRING and use it instead of current time

-f (ignored)

-m change only the modification time

-r, –reference=FILE
use this file’s times instead of current time

-t STAMP
use [[CC]YY]MMDDhhmm[.ss] instead of current time

–time=WORD
access -a, atime -a, mtime -m, modify -m, use -a

–help
display the help and exit

–version
output version information and exit

So say that you have a file called ‘file’ that I want to change date of
to say ‘Aug 21 1999 04:04′,
then you would do: touch -t 9908210404 file

For more info on this command do: man touch

——————————————————————————-

tr
translate characters, this command can change all upper case
characters to lower case characters in a file or substitute
all mumbers to some other characters etc.
tr’s syntax is: tr [arguments] <SET1> <SET2>
tr can be used with the following arguments:

-c, –complement
first complement SET1

-d, –delete
delete characters in SET1, do not translate

-s, –squeeze-repeats
replace sequence of characters with one

-t, –truncate-set1
first truncate SET1 to length of SET2

–help
display this help and exit

–version
output version information and exit

And the SET’s are as follows:

[:alnum:]
all letters and digits

[:alpha:]
all letters

[:blank:]
all horizontal whitespace

[:cntrl:]
all control characters

[:digit:]
all digits

[:graph:]
all printable characters, not including space

[:lower:]
all lower case letters

[:print:]
all printable characters, including space

[:punct:]
all punctuation characters

[:space:]
all horizontal or vertical whitespace

[:upper:]
all upper case letters

[:xdigit:]
all hexadecimal digits

[=CHAR=]
all characters which are equivalent to CHAR

Examples of tr is:
cat file | tr [:upper:] [:lower:] (change all uppercase to lower)
cat file | tr -d [:alnum:] (delete all numbers and chars)

For more info on tr, do: man tr

——————————————————————————-

traceroute
traceroute is a command that traces a route to an IP/host
and will give you the number of hops from your computer
to the remote computer, and will display the ping times
to each computer in the way.

traceroute has some arguments that I never needed to use
but if you feel curious about this command, feel free
to look at the manual pages for it: man traceroute

——————————————————————————-

ulimit
ulimit sets a limit for how much memory etc. users are allowed
to use.
It works like this: ulimit [arguments]
And the arguments can be the following:

-S     use the `soft’ resource limit
-H     use the `hard’ resource limit
-a     show all settings
-c     core file size (in blocks)
-d     data seg size (in kilo bytes)
-f     file size (in blocks)
-l     max locked memory (in kilo bytes)
-m     max memory size (in kilo bytes)
-n     open files (number)
-p     pipe size (512 bytes)
-s     stack size (in kilo bytes)
-t     cpu time (in seconds)
-u     max user processes (number)
-v     virtual memory (kilo bytes)

Say that I want to set a limit that users can only run 50
processes each, the I would do: ulimit -u 50

——————————————————————————-

umount
un mount, un mounts a mountpoint, say that you have mounted your
CD-rom drive on /mnt/cdrom then you would do: umount /mnt/cdrom
to unmount it.

I never used any arguments to this command, but if you wanna learn
about them, feel free to do: man umount

——————————————————————————-

unalias
unalias removes a defined alias, say that you have an alias
like this: alias du=’du -h’
And you want to remove it: then you simply do: unalias du
To remove all aliases do: unalias -a

For more info do: help unalias

——————————————————————————-

uname
uname gives info on the current system, and works as
this: uname [arguments]
The arguments can be the following:

   -a, –all         print all information
   -m, –machine     print the machine (hardware) type
   -n, –nodename    print the machine’s network node hostname
   -r, –release     print the operating system release
   -s, –sysname     print the operating system name
   -p, –processor   print the host processor type
   -v                print the operating system version
       –help         display this help and exit
       –version      output version information and exit

The most common way of using uname is: uname -a

——————————————————————————-

uncompress
uncompress uncompresses .Z files, for more info do: man uncompress

——————————————————————————-

uniq
uniq does by default take away duplica words out of a text,
which can be good if your sorting out a dictionary.
But `uniq` can also be executed with the following arguments:

-c, –count
prefix lines by the number of occurrences

-d, –repeated
only print duplicate lines

-D, –all-repeated
print all duplicate lines

-f, –skip-fields=N
avoid comparing the first N fields

-i, –ignore-case
ignore differences in case when comparing

-s, –skip-chars=N
avoid comparing the first N characters

-u, –unique
only print unique lines

-w, –check-chars=N
compare no more than N characters in lines

-N same as -f N

+N same as -s N

–help
display the help and exit

–version
output version information and exit

For more info on this command do: man uniq

——————————————————————————-

unset
this command will remove an alias or function.
It has the following options:

-v unset a variable only.
-f unset a function only.

By default unset will first try to unset as a variable and if that
fails it will try to unset as a function.

Here’s an example:

alien:~$ foo=bar
alien:~$ echo $foo
bar
alien:~$ unset foo
alien:~$ echo $foo

alien:~$

For more info, do: help unset

——————————————————————————-

unzip
unzip is the tool or command to unzip files, it works like this:
unzip [arguments] <file.zip>

unzip has some arguments I never used, do: unzip –help
to get a list of valid arguments.
Also feel free to do: man unzip

——————————————————————————-

updatedb
update the locate database, updatedb works like this:
updatedb [arguments] <pattern>
By default updatedb updates the locate database so it covers the
whole system and all it’s files, but has the following arguments:

-u Create slocate database starting at the root direc-
tory. This is the default behavior when called as updatedb.

-U path
Create slocate database starting at path path.

        -e dirs
               Exclude directories in the comma-separated list
               dirs from the slocate database.

        -f fstypes
               Exclude file systems in the comma-separated list
               dirs from the slocate database.

        -l <num>
               Security level.   -l 0 turns security checks off,
               which will make searches faster. -l 1 turns security
checks on. This is the default.

-q Quiet mode; error messages are suppressed.

-v Verbose mode; display files indexed when creating database

–help
Print a summary of the options to slocate and exit.

–version
Print the version number of slocate and exit.

If you have the whole system updataded in the locate databse,
to find a file all you have to do is to: locate <file>

For more info: man updatedb

——————————————————————————-

uptime
displays the current uptime (the time the system has been on).
with the load average.
It shows from left to right:
The current time, how long the system has been running,
how many users are currently logged on, and the system load
averages for the past 1, 5, and 15 minutes.

Also do: man uptime

——————————————————————————-

useradd
useradd adds a user account to the system.
useradd works like this: useradd [arguments] user

Here’s a cut & paste from it’s manual page (as usual).

-c comment
The new user’s password file comment field.

        -d home_dir
               The new user will be created using home_dir as the
               value for the user’s login directory. The default
               is to append the login name to default_home and use
               that as the login directory name.

        -e expire_date
               The date on which the user account will be dis-
               abled.   The date is specified in the format YYYY-
               MM-DD.

        -f inactive_days
               The number of days after a password expires until
               the account is permanently disabled. A value of 0
               disables the account as soon as the password has
               expired, and a value of -1 disables the feature.
               The default value is -1.

        -g initial_group
               The group name or number of the user’s initial
               login group.   The group name must exist. A group
               number must refer to an already existing group.
               The default group number is 1.

        -G group,[…]
               A list of supplementary groups which the user is
               also a member of. Each group is separated from the
               next by a comma, with no intervening whitespace.
               The groups are subject to the same restrictions as
               the group given with the -g option. The default is
               for the user to belong only to the initial group.

        -m      The user’s home directory will be created if it
               does not exist.   The files contained in skele-
               ton_dir will be copied to the home directory if the
               -k option is used, otherwise the files contained in
               /etc/skel will be used instead.   Any directories
               contained in skeleton_dir or /etc/skel will be cre-
               ated in the user’s home directory as well. The -k
               option is only valid in conjunction with the -m
              option. The default is to not create the directory
               and to not copy any files.

        -M      The user home directory will not be created, even
               if the system wide settings from /etc/login.defs is
               to create home dirs.

        -n      A group having the same name as the user being
               added to the system will be created by default.
               This option will turn off this Red Hat Linux spe-
               cific behavior.
        -r      This flag is used to create a system account. That
               is, an user with an UID lower than value of UID_MIN
               defined in /etc/login.defs. Note that useradd will
               not create a home directory for such an user,
               regardless    of    the    default    setting    in
               /etc/login.defs.   You have to specify -m option if
               you want a home directory for a system account to
               be created. This is an option added by Red Hat.

        -p passwd
               The encrypted password, as returned by crypt(3).
               The default is to disable the account.

        -s shell
               The name of the user’s login shell. The default is
               to leave this field blank, which causes the system
               to select the default login shell.

        -u uid The numerical value of the user’s ID.   This value
               must be unique, unless the -o option is used. The
               value must be non-negative. The default is to use
               the smallest ID value greater than 99 and greater
               than every other user. Values between 0 and 99 are
               typically reserved for system accounts.

When the -D argument is used useradd with either give the
default values or update them if there is more arguments.
The other arguments can be:

        -b default_home
               The initial path prefix for a new user’s home
               directory. The user’s name will be affixed to the
               end of default_home to create the new directory
               name if the -d option is not used when creating a
               new account.

-e default_expire_date
The date on which the user account is disabled.

        -f default_inactive
               The number of days after a password has expired
               before the account will be disabled.

        -g default_group
               The group name or ID for a new user’s initial
               group. The named group must exist, and a numerical
               group ID must have an existing entry .

        -s default_shell
               The name of the new user’s login shell. The named
               program will be used for all future new user
               accounts.

Also feel free to read the manual page: man useradd

——————————————————————————-

userdel
userdel removes a user from the system.
userdel works like this: userdel [argument] <user>
The only argument to this command is:
-r removes the users home directory, along with the user.

This will delete the users login and everything from the system.

userdel will not remove the user if he is currently logged
in to the system or have any processes running.
So make sure you kill all processes owned by the user,
if any, before removing his/her account.

To kill the all running processes owned by the same user
you can do the following command (change <user> to the username):

for pids in `ps U <user> | cut -c 1-6`; do kill -9 $pids ; done

——————————————————————————-

users
Display the currently logged in users.

——————————————————————————-

usleep
usleep is another version of the sleep command, but instead of beeing
told how many seconds to sleep, it sleeps in microseconds.
So `usleep 1000000` makes it sleep for 1 second.

——————————————————————————-

w
w is like a mix of who and finger, it’s used to see who’s logged
on to the system and will show the following:
login name, terminal, host, login time, idle time, JCPU (total cpu time
that user (terminal) takes up), PCPU (cpu time of the users current
process which is shown in the next field), what (process)

——————————————————————————-

wall
wall is a superuser command to send a string of text to all
consoles/terminals, wall can work either like: wall <string>
or: wall <file with string in it>
To wall special characters like “=)” you need to do it like
this: wall ‘<string> =)’

——————————————————————————-

wc
word count, works basicly like this: wc [argument] <file>
Where the arguments can be any of the following:

-c, –bytes, –chars   print the byte counts
   -l, –lines            print the newline counts
   -L, –max-line-length print the length of the longest line
   -w, –words            print the word counts
           –help             display this help and exit
           –version          output version information and exit

So to find out the number of words in a file called say “file1”,
you would do: wc -w file1
Or to find out the number of lines in the same file you would
do: wc -l file1

This little tool can prove to be very useful, though when you
use it with the -l/–lines argument it will only count lines that
contains any characters, if you wanna count all lines
including empty lines, use: grep -c . file1
or the same thing in another way: cat file1 | grep -c .

——————————————————————————-

whatis
whatis searches for words in the whatis database, say that you
are looking for a manual page about the `shutdown` command.
Then you can do: whatis shutdown
for more information, do: man whatis
Or: man apropos

——————————————————————————-

whereis
whereis looks for something just as the `which` command here below.
but looks for matches in more places, as the manual page directory’s.
It works like this: whereis [argument] <what-you-wanna-find>
Try this command a few times, and if you want to learn
more about it as it’s arguments and so do: man whereis

——————————————————————————-

which
which will tell you where a command is located, as if you
do: which shutdown
it will answer: /sbin/shutdown
This command will search your path for whatever you type after it.
This command is best used in scripts and functions, like this:

function whichrpm { rpm -qf `which $1`; }

The which command has some arguments, and more examples in it’s
manual page, so for more info do: man which

——————————————————————————-

who
who is a little command that shows you who’s logged on,
on what tty and at what time they logged on.
I never ever used this command with any arguments,
but if you want to learn more about this command do: who –help
or: man who

——————————————————————————-

whoami
displays your user name, same as `id -un`.
whoami can be used with the following arguments:
–help display this help and exit
–version output version information and exit

Not much more to say about this command.

——————————————————————————-

whois
whois is a tool that asks internic for information on a domain name.
This is only for .com .org .net etc.
If any luck it will give you the name and other info of the one that
registered the domain, and it’s name servers.

whois can also be used to do: whois user@host

For more info on this command do: man whois
Or: man fwhois

——————————————————————————-

yes
yes is a command that repeats the same thing over and over again,
it’s used as this: yes <string>
If no string or word is supplied it will repeat the character ‘y’.
yes can be used with the following arguments:

–version display the version and exit.
–help display the help and exit.

——————————————————————————-

zip
zip is a compression tool, to compress with zip do:

zip [arguments] <file.zip> <file1> <file2> etc.

The arguments can be the following:

-f   freshen: only changed files
-u   update: only changed or new files
   -d   delete entries in zipfile
-m   move into zipfile (delete files)
   -r   recurse into directories
-j   junk (don’t record) directory names
   -0   store only
-l   convert LF to CR LF (-ll CR LF to LF)
   -1   compress faster
-9   compress better
   -q   quiet operation
-v   verbose operation/print version info
   -c   add one-line comments
-z   add zipfile comment
   -@   read names from stdin
-o   make zipfile as old as latest entry
   -x   exclude the following names
-i   include only the following names
   -F   fix zipfile (-FF try harder)
-D   do not add directory entries
   -A   adjust self-extracting exe
-J   junk zipfile prefix (unzipsfx)
   -T   test zipfile integrity
-X   eXclude eXtra file attributes
   -y   store symbolic links as the link instead of the referenced file
   -R   PKZIP recursion (see manual)
   -h   show the help
-n   don’t compress these suffixes

To uncompress a zip file, use the `unzip` command.

——————————————————————————-

And that is most of the commands you’ll ever encounter while scripting or
using a *nix system.
There are LOADS of other commands, but not many that are as used as these
I just explained.

There are more really useful commands that I never seen as default
on any system aswell, like pgp and gpg, I havent included those since
there full documentation comes with the same package as that
command/application if you download it.

So, as I said these are the most useful commands, but if someone out there
think I missed some really useful command send me a mail and I’ll add it.

===============================================================================
10 – Other Frequently asked questions with answers.
===============================================================================

Q: How can I play an .au file ?
A: The file suffix .au means it’s an audio file, so you can either do
   the same as for mp3’s: mpg123 file.au
   or you can (since .au files are raw audio): cat file.au > /dev/dsp
   or: cat file.au > /dev/audio

Q: What exactly is bash ?
A: If you have read this tutorial you would know … it’s a shell type.

Q: I wanna make some sub-directory’s to /usr/local/ but I’m to lazy to write
almost the same line over and over again, is there any easier way ?
A: Yes there is: mkdir /usr/local/{dir1,dir2,dir3}

Q: I have a dir with files like this: file.1 file.2 file.3 etc.
is there any way I can list say, file.3, file.4, file.6, file.9 only
without using grep ?
A: Yes there is: ls file*[3469]*

Q: I want to remove some files with wildcards included in the command
(rm -rf .??*), is there any way I can see what the command will remove
before I actually do the command ?
A: Yes there is: echo rm -rf .??*

Q: How can I remove file names that are/have special characters like a file
   named: -!?* !!?
A: Do this: rm ./-\!\?\*\ \!\!\?
   The ./ makes sure it will look in the current directory, and the \
   (back slashes) will make sure that the special characters special meaning
   is over looked, so they are treated just like any other character.

Q: I accidently deleted something on my system, is there any way
   of getting it back ?
A: Yes there is, read this file /usr/doc/HOWTO/mini/Ext2fs-Undeletion
   (or /usr/doc/HOWTO/mini/Ext2fs-Undeletion.gz)
   This is also good knowledge if someone *hacks* your system
   and think they are safe just because they deleted the logs.
   Or you can download a program called ‘recover’ from www.freshmeat.net

Q: How do I compile my kernel ?
A: Read this file: /usr/doc/HOWTO/Kernel-HOWTO

Q: Can I make a variable read-only so noone can change it ?
A: Yes you can: readonly variable_name
   As say that I have a variable: $myvar
   Then I would do: readonly myvar
   And to display all the read-only variables just do: readonly

Q: How can I display all the set variables ?
A: With the command: set
To get the eviorment use this command: env
And to display the system variables, type a $ and press TAB.

Q: Something is wrong with a script, but I dont know what, how can I find out ?
A: by doing this: /bin/sh -x <scriptname>
+ means that the command was successful.
– means that the command was unsuccessful.

Q: I’m using hexedit and simlar commands alot, but I’m getting to lazy to
   find out where all the binarys live, isn’t there any faster way of
   opening a binary or script that’s in my $PATH then to locate, find or
   something like that and then go from there ?
A: Well, I dont know how much faster it is, but you can always
   do this: hexedit `which <file>`

Q: How can I list only the directorys in a directory without the files ?
A: Well, some distros has an alias “lsd”, and it does: ls -d */

Q: How can I transfer a file if the computer doesn’t have any FTP ?
A: If you wanna actually copy a file to a place that dont have ftp
   or for some other reason you can’t use ftp, there is 2 commands that can
   do this: scp (secure copy – requiers ssh)
   And: rcp (remote copy – requiers rlogin)
   They work like this:
   scp local.file user@host.domain.com:/remote/directory/
   rcp local.file user@host.domain.com:/remote/directory/

Q: Is there any way I can view my processes so I can see the free stack,
father processes siblings and children etc. ?
A: Yes there is, press: Ctrl + Scroll-Lock

Q: Is there any way I can view the memory buffers etc. ?
A: Yes there is, press: Shift + Scroll-Lock

Q: Is there any way to get some info from the stack ?
A: Yes there is press: AltGr + Scroll-Lock

Q: My volume is really low when I play stuff, how can I change it ?
A: Use the program `aumix` it should be on most systems by default,
and it’s pretty self explanatory.

Q: I think it’s a pain pressing upp arrow until I reach the command I want
to use, that is to long to type again, is there any faster way ?
A: Yes, press Ctrl+R and type something that matches a previously used
command, and just press enter to execute it or Ctrl+C to cancel.

Q: Is there any console based mpeg movie players ?
A: Not that I know of, but if there is, I’d like to know myself.

Q: How can I take a screenshot without having to install Gimp or something
   like that ?
A: Well, the easyest way of taking a screen shot in X is to do the
   following command: import -window root foo.jpg
   That will dump a screen shot as foo.jpg, in your current directory.

Q: How can I import variables from one script to another, like a config file ?
A: You can read all variables from a file by doing “. <file name>”, say
   that you have a file called myvars and you want to you those variables
   in a script, then you add the line: . myvars
   in the beginning of the script, after the #!/bin/bash line.
   The . is actually a command, that reads and executes commands in a file,
   which here works to imported the variables since they are executed
   from within the script.

Q: I’m using `port sentry` as a firewall controll software, now my routing
   table is over full, how can I take away all that’s routed to ‘localhost’
   in one command or string ?
A: Well like this: for ips in `route | grep local | cut -c 1-14`; do route del -host $ips gw 127.0.0.1 2>/dev/null ; done
   That should do the trick.

Q: If I’m in a directory full or rpm files and I wanna find out which rpm that
contain say the file vga.h, how would I do that ?
A: Well you can do this:
for foo in `ls -1 *.rpm`; do rpm -qlp $foo | grep vga.h 1>/dev/null 2>&1 && echo $foo; done

Q: Is there any place I can find out where all the ^ (Ctrl) characters mean ?
A: Yes, look in the ascii table below, it works like this:
   M is the 13’th character in the alphabet, and in the ascii table
   013 (dec) has the value CR which means Carriage Return.
   this means that ^M (Ctrl+M) is the same as pressing the return button.
   And ^A which is 001 (dec) is Start of Header, in other words take the
   cursor to the beginning of the current line.

Q: How do I write stuff in hex code ?
A: Well, like this:

——————————————————————————-
ASCII codes
——————————————————————————-

ASCII Table (7-bit)

       Decimal   Octal   Hex    Binary     Value
       ——-   —–   —    ——     —–
         000      000    000   00000000      NUL    (Null char.)
         001      001    001   00000001      SOH    (Start of Header)
         002      002    002   00000010      STX    (Start of Text)
         003      003    003   00000011      ETX    (End of Text)
         004      004    004   00000100      EOT    (End of Transmission)
         005      005    005   00000101      ENQ    (Enquiry)
         006      006    006   00000110      ACK    (Acknowledgment)
         007      007    007   00000111      BEL    (Bell)
         008      010    008   00001000       BS    (Backspace)
         009      011    009   00001001       HT    (Horizontal Tab)
         010      012    00A   00001010       LF    (Line Feed)
         011      013    00B   00001011       VT    (Vertical Tab)
         012      014    00C   00001100       FF    (Form Feed)
         013      015    00D   00001101       CR    (Carriage Return)
         014      016    00E   00001110       SO    (Serial In)
         015      017    00F   00001111       SI    (Serial Out)
         016      020    010   00010000      DLE    (Data Link Escape)
         017      021    011   00010001      DC1 (XON) (Device Control 1)
         018      022    012   00010010      DC2       (Device Control 2)
         019      023    013   00010011      DC3 (XOFF)(Device Control 3)
         020      024    014   00010100      DC4       (Device Control 4)
         021      025    015   00010101      NAK    (Negative Acknowledgement)
         022      026    016   00010110      SYN    (Synchronous Idle)
         023      027    017   00010111      ETB    (End of Trans. Block)
         024      030    018   00011000      CAN    (Cancel)
         025      031    019   00011001       EM
         026      032    01A   00011010      SUB
         027      033    01B   00011011      ESC    (Escape)
         028      034    01C   00011100       FS    (File Separator)
         029      035    01D   00011101       GS
         030      036    01E   00011110       RS    (Request to Send)
         031      037    01F   00011111       US
         032      040    020   00100000       SP    (Space)
         033      041    021   00100001        !
         034      042    022   00100010        ”
         035      043    023   00100011        #
         036      044    024   00100100        $
         037      045    025   00100101        %
         038      046    026   00100110        &
         039      047    027   00100111        ‘
         040      050    028   00101000        (
         041      051    029   00101001        )
         042      052    02A   00101010        *
         043      053    02B   00101011        +
         044      054    02C   00101100        ,
         045      055    02D   00101101        –
         046      056    02E   00101110        .
         047      057    02F   00101111        /
         048      060    030   00110000        0
         049      061    031   00110001        1
         050      062    032   00110010        2
         051      063    033   00110011        3
         052      064    034   00110100        4
         053      065    035   00110101        5
         054      066    036   00110110        6
         055      067    037   00110111        7
         056      070    038   00111000        8
         057      071    039   00111001        9
         058      072    03A   00111010        :
         059      073    03B   00111011        ;
         060      074    03C   00111100        <
         061      075    03D   00111101        =
         062      076    03E   00111110        >
         063      077    03F   00111111        ?
         064      100    040   01000000        @
         065      101    041   01000001        A
         066      102    042   01000010        B
         067      103    043   01000011        C
         068      104    044   01000100        D
         069      105    045   01000101        E
         070      106    046   01000110        F
         071      107    047   01000111        G
         072      110    048   01001000        H
         073      111    049   01001001        I
         074      112    04A   01001010        J
         075      113    04B   01001011        K
         076      114    04C   01001100        L
         077      115    04D   01001101        M
         078      116    04E   01001110        N
         079      117    04F   01001111        O
         080      120    050   01010000        P
         081      121    051   01010001        Q
         082      122    052   01010010        R
         083      123    053   01010011        S
         084      124    054   01010100        T
         085      125    055   01010101        U
         086      126    056   01010110        V
         087      127    057   01011111        W
         088      130    058   01011000        X
         089      131    059   01011001        Y
         090      132    05A   01011010        Z
         091      133    05B   01011011        [
         092      134    05C   01011100        \
         093      135    05D   01011101        ]
         094      136    05E   01011110        ^
         095      137    05F   01011111        _
         096      140    060   01100000        `
         097      141    061   01100001        a
         098      142    062   01100010        b
         099      143    063   01100011        c
         100      144    064   01100100        d
         101      145    065   01100101        e
         102      146    066   01100110        f
         103      147    067   01100111        g
         104      150    068   01101000        h
         105      151    069   01101001        i
         106      152    06A   01101010        j
         107      153    06B   01101011        k
         108      154    06C   01101100        l
         109      155    06D   01101101        m
         110      156    06E   01101110        n
         111      157    06F   01101111        o
         112      160    070   01110000        p
         113      161    071   01110001        q
         114      162    072   01110010        r
         115      163    073   01110011        s
         116      164    074   01110100        t
         117      165    075   01110101        u
         118      166    076   01110110        v
         119      167    077   01110111        w
         120      170    078   01111000        x
         121      171    079   01111001        y
         122      172    07A   01111010        z
         123      173    07B   01111011        {
         124      174    07C   01111100        |
         125      175    07D   01111101        }
         126      176    07E   01111110        ~
         127      177    07F   01111111      DEL

——————————————————————————-

Say that you want to echo “Hi” with hex code, you do this:

echo -e “\x048\x069”

The \x part is to let `echo -e` know that it’s hexa decimal code.
You can even hide commands like that.

Here is a script example of hiding the `top` command in hex and execute it:

——————————————————————————-

#!/bin/bash

hexcode=’\x074\x06F\x070’

`echo -e $hexcode`

——————————————————————————-

This will execute what echo echos, due to the “`”‘s.
So that script will actually start the `top` command.

——————————————————————————-

Another question I got a while back is how to make a DWORD (Double Word),
that means how to rewrite an address or IP to hex/oct/dec.

And it’s not that hard, all it takes is some mathematics.
It works like this:

There are several methods, but let’s start with the Decimal way
of making a DWORD.
Say you have IP: 127.0.0.1
then you do:
127 * 16777216 = 2130706432
0 * 65536      = 0
0 * 256        = 0
1 * 1          = 1
Sum:             2130706433

Or if you have the IP: 123.123.123.123
123 * 16777216 = 2063597568
123 * 65536    = 8060928
123 * 256      = 31488
123 * 1        = 123
Sum:             2071690107

Note:
      16777216 = 2^24
         65536 = 2^16
           256 = 2^8
             1 = 2^0

Next method is to convert it to HEX, OCT etc, to convert from dec to oct etc.
you can either use the ascii table a few lines up, or you can download
a program called ascii from www.freshmeat.net.
Last time I saw it it was located at:
http://freshmeat.net/projects/ascii/download/ascii-3.0.tar.gz

So assuming you have downloaded that and and wanna covert 127.0.0.1 and
123.123.123.123 to HEX DWORDs, do this:

alien:~$ ascii 127 0 0 1
ASCII 7/15 is decimal 127, hex 7f, octal 177, bits 01111111: called ^?, DEL
Official name: Delete

ASCII 5/7 is decimal 087, hex 57, octal 127, bits 01010111: prints as `W’
Official name: Majuscule W
Other names: Capital W, Uppercase W

ASCII 3/0 is decimal 048, hex 30, octal 060, bits 00110000: prints as `0′
Official name: Digit Zero

ASCII 3/1 is decimal 049, hex 31, octal 061, bits 00110001: prints as `1′
Official name: Digit One

alien:~$

Take the hex numbers after the decimal of 127, 0 and 1 and you’ll come
to the conclution that 127.0.0.1 in a hex DWORD is: 7F303031

You can use OCT the same way .. with as many leading 0’s as you please

0173.0173.0173.0173 or 000173.00000173.000173.000000000000000000000173,
it still means IP 123.123.123.123

And ofcorse to add on the confusion you can mix the methods.
0173.0x7b.00173.123

Now there is even more to this like that you can add any multiple of the
number 4294967296 (2^32) to the number without the IP changing ….
But let’s not get into that ….

So basically typing:
http://0173.0x7b.00173.123/
in your web browser will end you up at IP 123.123.123.132 (which doesnt excist)
but the idea is the same for everything, so if you see some lame spammer
thinking that you wont know from what address he sent something …
The just back count it and send abuse mail to his internet service provider.

——————————————————————————-

If someone has more questions mail, them to me at: alien@ktv.koping.se
maybe I’ll include them in the tutorial, but I’ll do my best to answer
the questions anyway.

===============================================================================
10 – Basics of the common UNIX and Linux text editors.
===============================================================================

Here we go with the text editors vi, ed and emacs.
ed is just explained for historical reasons.

——————————————————————————-
Most commonly used VI commands
——————————————————————————-

Here we go with the vi commands, these are unlogical but still good to know
because all computers doesn’t have emacs, joe, pico and so on.
Solaris / SunOS comes default with vi as only text editor.
Vi has 2 basic modes, command mode and edit mode, you change between them
by pressing the Esc button, and to start to edit a file you must have a
free line, which you get by pressing, Esc followed by `o`.
vi is bound to be the hardest and most confusing text editor to learn,
and it has LOTS of commands, I included just a few of the most used
commands.

So here we go with the vi commands:

Inserting text

esc + i                 insert text informant of the cursor
esc + a                 append text after the existing text
esc + O                 opens new line above the current line
esc + o                 opens new line under current line (insert mode)

Deleting text

esc + x                 deletes one character
esc + 5x                deletes five charters
esc + dw                deletes a word
esc + 5dw               deletes five words
esc + dd                deletes the whole line
esc + D   deletes the line from cursor and forward
esc + d)                deletes the sentence from cursor and forward
esc + d(                deletes the sentence from cursor and backwards
esc + u                 undelete

Note: esc + d) or d( removes the sentence from cursor and forward/backwards
until it reaches a dot “.”

Moving around in VI:

Make sure you are in command mode and the following letters will do:

j               moves you down
k               moves you up
h               moves you left
l               moves you right

Finding Text

Hit esc then type in a / you then go to the bottom of the screen
where you will see your / type in the text to look for.
ie. /Linux
that will find the word `Linux` in the open file.

Replacing Text

Hit esc and do: :start,stop,s/s_text/r_text/g

:               indicates that this is an ex command
start           is the starting line number
stop            is the stopping point
s               is the substitute command
s_text          is the search string (the text you are looking for )
r_text          is the text you are replacing with
g               is global

Example:

Esc + :5,8,s/l/ll/g

This would replace all “l”‘s with “ll” on lines 5 to 8.

Note to Replacing Text:
Line numbers can also be:
. current line
$ last line

Basic save & quit commands

Hit Esc and do a : where after you can type the commands.

w write (save)
q quit
! force

ie. :q! or :wq

To create control characters do:

Ctrl+V Ctrl+<the character>

Example:

Ctrl+V Ctrl+A

That will create a ^A character.

(These last 3 commands are very alike ed commands)

Another useful thing in VI is split-screen mode, so you can edit 2 files
at once, this is:

:split

Just press Esc and type “:split”.
You can do this in most big editors ….. but ofcorse in another way, you’ll
see when you’re reading the emacs section.

——————————————————————————-
Most commonly used ED commands
——————————————————————————-

ed is a very very old line editor, and the grand father of most editors,
perhaps even the grandfather of all editors, it dates back to the time of
the old CP/M machines, and is the father of the old DOS edlin line editor.
So out of historical perspective, it can be fun to know how to operate ed.

Creating a file in ed:

alien:~$ ed newfile
newfile: No such file or directory

Don’t worry, as soon as you save it it will create it.
ED is pretty simple, here’s an example (the “(ed says)” and “(we type)” is
just there to make it easier to follow the editing in this tutorial and is
not there in reality):

alien:~$ echo “abcd” >> newfile; echo “efgh” >> newfile; echo “ijkl” >> newfile
alien:~$ ed newfile
15 (ed says)
1,$ n (we type)
1       abcd (ed says)
2       efgh (ed says)
3       ijkl (ed says)
1 (we type)
abcd (ed says)
s/ab/ll (we type)
llcd (ed says)
$ n (we type)
3       ijkl (ed says)
a (we type)
here we end (we type)
. (we type)
w (we type)
27 (ed says)
q (we type)
alien:~$

Not all that hard is it ?
Here’s a list of the most basic commands for ed:

1,$ n    displays all lines with numbers
$ n display last line, with number
2 n      takes you to line 2
s/new/old       replaces old with new
a        takes you to editor mode
.        takes you to command mode
d        deletes line
w write file (save)
q quit

——————————————————————————-

The final thing in this tutorial is a really quick look at emacs commands:

Most commonly used Emacs commands
——————————————————————————-

^A Cursor to the beginning of line
^E Cursor to the end of line
^K Deletes rest of line forward
^D Deletes current character
^L Horizontally center the current line
^S Search for a word forward in the file
^R Search for a word backwards in file

^Q Followed by Ctrl+<anything>, gives the real control character in a text file

^X ^F Open file
^X ^- ^- Undo
^C+Shift+- Undo
^X ^C ! Quit without saving
^X 2 split screen (horizontaly)
^X 3 split screen (verticaly)
^X O move to other screen (if in splitscreen mode)
^X ^W Save As
^X ^S Save

(^X 1 to get back a single window from splitscreen mode)

Shift+Esc Shift+5: Replace query (press y to replace words)
Meta+backspace: Deletes rest of word backwards (note “Meta” == “Alt”)
Home: Takes cursor to the top of the file (Or equal to ^A)
End: Takes cursor to the end of the file (Or equal to ^E)
Delete: Deletes current character
Page Up / Page Down: Does what they say
Meta+X: Will load any emacs plugin, you may type any plugin name after pressing
the Meta+X (Alt+X), if you press TAB here once you will get a list of the
commands, if you type ‘a’ followed by a tab you will get all commands
starting with a and so on …. try: Meta+X doctor to try the
interactive eliza bot, or try telnet, ftp, webjump or shell.

To reach the menus “Buffers Files …” etc. press F10
and if you wanna get out of the menus press ^G.

You may think that all this is weird, but know that emacs use to work
as a VERY primitive window manager, before the times of X.

Backspace and the arrow key’s works as normal.

A tip is tp press: ^X then press 2 then press ^X and then O, now press
Meta+X and type ‘shell’, and you should have a split window, with a
shell in the lower one, so you can code or write in the upper one
at the same time as you have a shell in the lower one.
To change between the windows simply press: Ctrl+X and then press: o
A note is that if you want to run BitchX in the shell part you need
to start it with: BitchX -d, to get it in dumb terminal mode.

Usless or obsolete commands:

^I TAB
^O Move text forward
^P same as UpArrow
^F same as RightArrow
^J Enter/Return
^B same as LeftArrow
^N same as DownArrow
^M Enter/Return

^U Del deletes 4 characterss backwards
^U ^U Del deletes 16 characterss backwards
^U ^U ^U Del deletes 64 characterss backwards

All you really need to know to start using emacs is how to save and quit.

( ^X ^S ^X ^C will save and quit, a tip is: hold down ^ (Ctrl) and
press X S X C )

===============================================================================
——————————————————————————-
===============================================================================

This should be enough for you to start to script in bash, and make useful
scripts.
The only thing that limits what you can do is your imagination (well almost).

Go over this tutorial several times so you really understand everything.
If you accomplish that, you have a really good chance of learning UNIX well.

And that’s what it’s all about, to learn new things and explore new ways.
As long as you learn you live, not the contrary.

This tutorial turned out rather large, but I hope that those of you out there
that have the determination to learn shell scripting, also have the patinace
to read it all, and if not, you can always use it as a small dictionary.

I’ve got the question many times, which Linux distribution is the best ….
The question in it self is pointless and as ilitterat as asking
what version linux is up to….
The later question can only be answerd with a kernel version number,
and that is what Linux is, Linux is the kenrel and all distributions
use the same kernel, everything else in the system is just “stuff around
the kernel”, to this point I’ve found that Mandrake is the distibution
that is most compleat for my needs, and it’s suitable for beginners
aswell as for proffessionals, and it has nice configuration tools
that have been written especially for Mandrake.
But as I said, a Linux is a Linux, and the main difference between different
distributions is the package manager, where of rpm is the most stanard
and accepted, though I find Debians dpkg good aswell.
This is to the difference of distributions that have no indiginous package
manager like Slackware, that emulates a package manager with it’s .tgz
package format (note that .tar.gz is not .tgz since .tgz should have it’s
packages compressed with there path beginning from / )
Now there is nothing wrong with that if you like to compile most stuff on the
system your self, and many people preffer to do that.

My conclution is that the best distrinution is the one you personally
like the best, the one that fits _your_ needs.

So anyway, when you know bash scripting well enough, my suggestion is to
learn C programming, which, if you look at it with bash behind you,
isn’t that hard.

So, I better go to bed and stop this nonses now.

Happy scripting all of you out there.

===============================================================================
————— Written by Billy Wideling <-> alien@koping.net —————-
===============================================================================

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