Short reference - Linux commands, files, configurations etc

I haven't updated my command cheat sheat quite a while, but well today I found some time. Have fun hope it helps - Yuriy.

Short reference - Linux
(Commands, Directories, Configuration files/Scripts) 

Linux command	Description
example	start example where example is a program found in the $PATH
./example	start example (allocated in current dir.)
adduser	add a user
rmuser	remove a user
passwd	change password
cd x or cd /x	go to directory x
cd .. or cd ../ or cd /..	go back one directory
pwd	Show current directory
ls or dir	list a directory
ls -al	Formated listing with hidden files
date	Show current date/time
cal	Show this months callender
uptime	Show uptime
w	Display who is online
whoami	Who are you logged in as
uname -a	Show kernel config
df	Show disk usage
du	Show directory space usage
du -sh	Human readable size in gigabyte
free	Show memory and swap usage
whereis app	Show possible locations of an app
which app	Show which app will be run by default
cat	display a textfile on the terminal Examples: cat /proc/meminfo - more memory info cat /proc/pci - list pci devices, interrupts, io cat /proc/cpuinfo - cpu info cat /proc/version - kernel and gcc version info cat /proc/ioports – input/output range of devices cat /proc/devices - Displays various character and block devices that are currently configured. cat /proc/filesystems - Lists all file system types currently supported by the kernel. cat /proc/mdstat - Contains current information on multiple-disk or RAID configurations on the system, if they exist. cat /proc/mounts - Lists all mounts currently used by the system. cat /proc/partitions - Contains partition block allocation information.
cat > file	place standart input into a file
touch file	create or update file
more file	Displays the file - paging through text one screen at a time
less file	Displays the top of the file you can use the arrow keys and the Page-Up and Page-Down keys to move through the file
head file	first 10 lines of a file.
tail file	last 10 lines of a file
tail -f file	output contents of a file as it grows
mv x y	move or rename file x to file y
cp x y	copy file x to file y
rm -f x	force remove a file
rm -rf dir	rm -rf /old_stuff - correct rm -rf / old_stuff – common mistake leaving space between / and the directory name. This will wipe your system
mkdir x	make a directory
mkdir x	make a directory
rmdir x	remove a directory
rm -r x	remove directory x and all its underlying files
man x	get a manual page about command x
less x or more x	view text file x
echo	print something on the screen mainly used in scripts
mc	similar to Norton Commander in DOS
mount	to make a device usable to the system (CD-ROM,other HDD)
umount	remove the device from being usable to the system
halt	to shutdown. It will also power off if APM or ACPI is being used
reboot or ([ctrl] + [alt] + [del])	to reboot the system
chmod <permissions> <file>	change file permissions
chown <owner:group> <file>	change file ownership
ls -l x	perform a detailed directory listing for file or directory x
ln -s file link	make a symbolic link to "file" called "link"
top	view memory status (q to quit)
ps	to view all running processes
ps aux	ps with mored detail
kill x	to terminate process x (x is PID from ps)
kill pid	kill processes with pid 'pid'
killall -KILL pgm	to kill the program called pgm
killall -HUP pgm	to force program pgm to restart - used in case configuration is changed
killall proc	Kill all processes named proc
bg	List stoped/background jobs, resume stopped job in the background
fg	Bring most recent jobs to foreground
fg n	Brings job m to foreground
lilo	to write boot information changes to disk
ldd	shows the needed shared libraries
ldconfig	updates shared libraries
lsmod	shows loaded modules
Searching	Description
find x -name y -print	find file y, begin the search from within directory x and print the results to the screen
grep pattern files	Search for pattern in files
grep -r pattern dir	Search recursively for pattern in dir
command | grep pattern	Search recursively for pattern in dir
locate file	Find all instances of file
Networking	Description
whois domain	Get whois for domain
dig domain	Get DNS for domain
dig -x host	Reverse lookup host
wget -c file	Continue stopped download
wget -r url	Recursively download files from url
ssh user@host	Connect to host as a user
ssh -p port user@host	Connect using port p
ssh -D port user@host	Connect and use bind port
sshfs name@server:/path/folder /path/mount	Mount filesystem over ssh
ssh -t reachable_host ssh unreachable_host	Ssh trough host in the middle
python -m SimpleHTTPServer	Server current directory at http://$HOSTNAME:8000
Linux directories	Directory function
/	the root of the directory tree
/dev	the device pointer directory all devices have an entry here
/bin	main CLI executables
/sbin	main CLI system executables
/boot	location of the kernel and boot information required to boot the system
/etc	system configuration files
/root	root user home directory
/home	normal user base directory
/lib	system libraries and kernel modules
/usr	main user binary,documentation, library location eg. XFree86 and other X apps are here
/opt	extra binary/documentation,library location - eg.KDE
/var	system log files,spoolers,etc
/tmp	temporary folder for running applications that need temp files
/proc	includes files with information about the system
/mnt	filesystem mount point for devices (cdrom, usb etc.)
Linux configuration/script file	Description
/etc/lilo.conf	boot loader configuration file – you must run "lilo" after any changes
/etc/modprobe.conf	kernel module loader configuration used by the modprobe command
/etc/inittab	system runlevel configuration file - tells init what to do for each runlevel
/etc/fstab	filesystem mounting configuration file - used by the mount command
/etc/ld.so.conf	library configuration file - used by the ldconfig command to find libraries
/etc/inetd.conf	tcp wrapper configuration - used to start ftp and other network daemons
/etc/hosts	local host resolution file - manually enter hosts you want to connect to if they are not on DNS
/etc/HOSTNAME	system hostname file
/etc/profile	system defaults for bash login default paths,colours,etc
/etc/rc.d/rc.0	system halt script - run when you issue halt
/etc/rc.d/rc.6	system reboot script - run when you issue reboot or [ctrl] + [alt] + [del]
/etc/rc.d/rc.K	runlevel 1 or system administration mode
/etc/rc.d/rc.S	main system boot script - run when you boot up
/etc/rc.d/rc.M	main local startup script - activates other services you have chosen
/etc/rc.d/rc.sysvinit	SysV Init script starter
/etc/rc.d/rc.inet1	network startup script
/etc/rc.d/rc.modules	system module loader - run at startup
/etc/rc.d/rc.hotplug	hotplug starter script - for USB and PCI hotplug devices
/etc/rc.d/rc.pcmcia	pcmcia service script - for use with laptops
/etc/rc.d/rc.local	local startup script for user space programs
/etc/X11/xorg.conf	Xorg configuration file

Directories/files	Permission	Description
/var/log	751	Directory containing all log files
/var/log/messages	644	System messages
/etc/crontab	600	System-wide crontab file
/etc/syslog.conf	640	Syslog daemon configuration file
/etc/logrotate.conf	640	Controls rotating of system log files
/var/log/wtmp	660	Who is logged in now. Use who to view
/var/log/lastlog	640	Who has logged in before. Use last to view
/eto/ftpusers	600	List of users that cannot FTP
/etc/passwd	644	List of the system’s user accounts
/etc/shadow	600	Contains encrypted account passwords
/etc/pam.d	750	PAM configuration files
/etc/hosts.allow	600	Access control file
/etc/hosts-deny	600	Access control file
/etc/lilo.conf	600	Boot loader configuration file
/etc/securetty	600	TTY interfaces that allow root logins
/etc/shutdown.allow	400	Users permitted to ctrl-alt-del
/etc/security	700	System access security policy files
/etc/rc.d/init.d	750	Program start-up files on Red Hat systems
/etc/init.d	750	Program start-up files on Debian systems
/etc/sysconfig	751	System and network config files on Red Hat
/etc/inetd.conf	600	Internet SuperServer configuration file
/etc/cron.allow	400	List of users permitted to use cron
/etc/cron.deny	400	List of users denied access to cron
/etc/ssh	750	Secure Shell configuration files
/etc/sysctl.conf	400	Contains kernel tunable options on recent Red Hat