Getting started with *nix

This is a quick and by no means comprehensive reference for handy little tid bits you can use in red hat linux, and various other unices. For more information on any command, dont forget to use 'man' and 'info' pages.

Quick Command Reference:

DOS/WINDOWS and Linux Compared
DOS Command	Linux Command	Purpose
CD	cd	Change directory
DIR	ls	List the contents of a directory
CD	pwd	shows your full location in the filesystem
MOVE	mv	Move files
COPY	cp	Copy files
DEL	rm	Remove files
DELTREE	rm -r	Recursive delete, wipe directory and its contents, use rmdir for empty dir
REN	mv, rename	Rename files
EDIT	pico/vim/vi/nano	Edits files with simple text editor
TYPE	less or more or cat	View files

User Management and Permission Commands
Command	Function	Basic Syntax
su	Login as another user account	su -[user]
adduser	Add a user account(only availble to root)	adduser <account name>
passwd	Change a user's password	passwd <account>
chmod	Change permissions for files and folders	chmod <permissions> <target>
chown	Change ownership of files and folders	chown <user>:<group> <target>

Process Management
Command	Function
ps	Display processes currently running
ps aux	More informative ps display
top	Automatically refreshing list of running processes
kill <process id>	kill a processs with teh specified process id
kill -9 <process id>	kill a stubborn process

Installing Software (redhat and mandrake packages only)
Command	Function
rpm -ivh <pakcage file>	Install a new package
rpm -uvh <package file>	Upgrade a package
rpm -e <installed package>	uninstall a package
rpm -q <package>	Find out if a particular package is installed
rpm -q --requires <package file>	Find out a packages dependencies
rpm -qlp <package>	Lists all the files stored within a package
rpm -qix <package>	read a description of the installed package
rpm -qixp <package file>	read a description of an uninstalled package
rpm -v <installed package>	verify an installed package

Commands for Common tasks
Command	Function	Syntax
locate	Locates a specific file	locate <file name>
ln	Creates a link to another file	ln -s <target> <link name>
xhost	Add/Remove X access to your dislpay	xhost +[host name]
du	Shows disk usage of a file or directory	du <directory>
df	Shows free disk space on mounted filesystems	df
tar	Create and extracts the contents of .tar and .tar.gz files	tar -zxvf <filename.tar.gz> Extracts archive tar -cxvf <source> <filename.tar.gz> creates archive
tail	shows the bottem lines of a text file. Generally used with log fils to show the most recent data	tail <options> <filename>
reboot	Reboots the machine	reboot
shutdown	Shuts down the machine	shutdown <options> <time>

Popular Configuration files
Application or Service	Configuration file	Description	Initiate Changes
Samba	/etc/samba/smb.conf <redhat> /etc/smb.conf <mandrake>	Configures winows file and print sharing using the SMB protocol. SAmba allwos linux and windows machines to share files, pirnters, accounf information and more.	Service samba restart
LILO	/etc/lilo.conf	The linux loader. LILO is a samll program that launches when you start yoru machine, and allows your to choose between different operating systems, as well as different linux kernels	lilo
Filesystems	/etc/fstab	Teh filesystem table stores teh details of all your automatically mounted filesystems, as well as default optoins for temporary filesystems.	No action needed unless non-Linux filesystem permissions have been modified, when a user should log out and back in again
Modules	/etc/modules.conf	Specifids which modules to laod at boot time	reboot
X	/etc/X11/X86Config	Specifies your grahics card and montor, display size, display resolution and colour depth.	Log out and restart X
Default runlevel	/etc/inittab	There are six different runlevels on linux. Each runlevel changes teh services that are running. For example, runlevel 5 has a GUI login, runlevel 3 is console based, and runlevel 1 only a small set of servies, and is used fro troubleshooting. Edit the initdefault line to specify which runlevel to boot into.	Changes will be seen on reboot.

Bash Scripting:

built in shell variables:

$*	All of the script arguments starting from first
$#	The number of positional parameters
$-	current option flags
$$	Process ID of the Shell
$!	Process ID of the most recently executed background process
$0	Name of the shell
$_	The absolute filename of the shell script
$1,$2..$9	First, second through ninth arguments passed to the script

to see script executing line by line, try bash -x <scriptname>

Built in tests:

String Tests
[-n] STRING	the length of STRING is non-zero
[-z] STRING	the length of STRING is zero
STRING1 = STRING2	The strings are identical
STRING1 != STRING2	the Strings are not identical

Numerical Tests
NUM1 -eq NUM2	NUM1 is equal to NUM2
NUM1 -ge NUM2	NUM1 is greater or equal to NUM2
NUM1 -gt NUM2	NUM1 is greater than NUM2
NUM1 -le NUM2	NUM1 is less than NUM2
NUM1 -ne NUM2	NUM1 is not equal to NUM2

File Tests
FILE1 -nt FILE2	FILE1 is newer (modification date) than FILE2
FILE1 -ot FILE2	FILE1 is older than FILE2
-e FILE	FILE exists
-d FILE	FILE exists and is a directory
-f FILE	FILE exists adn is a regular file
Try man test for more tests

User Environment:

You can do nifty things with your dot files, for example, if you want to change your prompt, you can modify the PS1 variable in your .bashrc (if using bash that is) file. Some control characters are as follows:

Control Characters:

\a	A bell character
\d	The date: 'Weekday Month Date'
\e	An escape character
\h	The hostname, upto the first .
\H	The hostname
\n	The newline
\r	A carriage return
\s	The name of the shell
\t	the time in 24-hour HH:MM:SS format
\T	The time in 12-hour HH:MM:SS format
\@	The time in 12-hour am/pm format
\u	Username
\v	Bash Version
\V	Bash release number
\w	Current work directory
\W	BAsename of the current work directory
\!	History number of the current command
\#	Command number of the current command
\$	# for uid=0, else $
\\	A backslash
\[	Begin an escape sequence
\]	End an escape sequence

Colour Escape Sequences

Black	\[\033[0;30m\]
Red	\[\033[0;31m\]
Green	\[\033[0;32m\]
Brown	\[\033[0;33m\]
Blue	\[\033[0;34m\]
Purple	\[\033[0;35m\]
Cyan	\[\033[0;36m\]
Light Grey	\[\033[0;37m\]
Grey	\[\033[1;30m\]
Light Red	\[\033[1;31m\]
Light green	\[\033[1;32m\]
Light yellow	\[\033[1;33m\]
Light Blue	\[\033[1;34m\]
Light Purple	\[\033[1;35m\]
Light Cyan	\[\033[1;36m\]
White	\[\033[1;37m\]
Terminal Default	\[\033[0;0m\]

You can toggle the behaviour of the shell by setting and unsetting various shell options using the shopt command. To see what options are set for you, type 'shopt'. One handy non-default option is 'cdspell', you can enable it using: shopt -s cdspell

To see what other options do, look at man bash, and use '/' to search for each option you see outputed from shopt.

Extracted from the APC pocket book for linux (3rd edition + advanced) with my added comments.