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Useful Linux Commands and typical examples

Author:  Christophe Gevrey
Updated: [udate]

Area	Command	Description and/or Example
daemons	kill -9 PIDnumber	Kills the process PIDnumber that we want to (it stops running) kill -HUP PIDnumbe does the same. Kill -STOP PIDnumber Stopis until a new command the NumberPID process. Kill -CONT PIDnumber Resumes the numberPID process that we stopped before.
daemons	killall processname	Kills processname.
daemons	ps aux	Lists the aplications that are now running with his PID(Process IDentifier). ps aux | more Pauses between screens. Very useful to get information to kill a running process.
daemons	top	Shows the processes sorted by CPU use on real time, also free RAM and used SWAP.
daemons	xkill	Kills on X-windows the process that we select by clicking it with the mouse. It's the same as kill but on graphical mode. Hotkey: Ctrl+Alt+ESC
files	alias ls='ls --color=tty'	When you type ls you'll see color output but only if the output goes to screen (not a file) you could insert this line in ~/.bash_profile to always do it.
files	dd if=/dev/fd0 of=diskimagename	Makes a disk image and saves it on diskimagename file.
files	dd if=diskimagename of=/dev/fd0	Saves the diskimagename file to a floppy disk.
files	df	Shows free disk space.
files	du -c files	Shows the total size used by the files.
files	du -s directory	Shows the directory size.
files	echo $PATH	Shows the current path.
files	emacs filename	Edits the filename Ctrl+X Ctrl+S (save), Ctrl+X Ctrl+C (quit).
files	find /directory -name 'filename'	Searches from directory the specified filename.
files	for x in $(ls /directory) do echo $x done	A little bash script to loop on the files in a directory.
files	grep	Searches for a string on a file. cat file.txt | grep stringtolookfor
files	joe filename	Text editor.
files	less file	I'ts like a better more, allows to go up and down and doesn't load the all the entire file when you call it.
files	ln -s /mnt/cdrom/Mame/roms /usr/games/lib/xmame	Makes a soft link to the cdrom roms directory as if it was /usr/games/lib/xmame (xmame must not exist)
files	mke2fs /dev/hda2	Formats the second partition from the first hard disk using the Linux format (ext2).
files	more filename	Shows filename on screen (it's lik: type | more on ms-dos) .
files	mount /dev/hda1 /mnt/c -t vfat	Mounts fat32 partition.
files	pico filename	A basic text editor. Needs It's size in bytes is very low.
files	rm -rf directory	Deletes the directory and all the files within. No confirmation requiered.
files	sed	Changes a string for another one on a file (used with pipes).
files	sed 's/stringA/StringB/' filename > newfilename	Changes the first occurrence of stringA on filename for stringB and saves it in newfilename.
files	sed 's/stringA/stringB/g' filename > newfilename	Changes all the occurrence of stringA on filename for stringB and saves it in newfilename.
files	tail -f filename	Shows only the last lines of filename (good to follow on real-time log files).
files	tar -zcvf filename.tar.gz directory	Compresses in tarball the directory and all subdirectories into filename.tar.gz
files	tar -zxvf filename.tar.gz	Decompress filename.tar.gz
files	wc filename	Line count, word cound and byte count for the file.
files	whereis filename	Finds filename and says where it is using the internal data base, that must be updated. updatedb updates it.
files	zip -r targetfilename directory	Compress directory and all its folders on ficherodestino.zip
files	zip -r zipfilenameyouwant.zip desiredirectoryname	Compresses using zip the desiredirectoryname and all the subdirectories.
image	convert -resize 640x480 original.jpg modified.jpg	Converts image to 640x480
image	mplayer videoyouwant.avi -vo aa	Plays the video on ascii art.
network	/etc/network/interfaces	Edit this file to change IP on Debian
network	ifconfig	Shows your IP also is used to configure your network card.
network	ncftp	An improved ftp client for console
network	netstat -lnp --ip	If you type it being root, will display current running daemons.
network	scp root@192.168.0.201:/boot/vmlinux .	Copies the file vmlinux remote from the host 192.168.201 via ssh to current directory.
network	wget -c --passive-ftp ftp://filename	Downloads the file or continues the download using FTP passive mode.
network	wget -c http://filename	Downloads the requested filename or continues the download if the connection was lost.
network	wget -rl 4 http://domainname	Downloads the website and all files on it until level 4
sound	mpg123 -q /directory/*.mp3 &	Plays in background from the shell the .mp3 music files allocated on the directory.
system	/sbin/hdparm -d 1 /dev/hda	Sets using_dma bit to 1 to enable Ultra-DMA access to disk.
system	/sbin/hdparm -tT /dev/hda	Performs a timing benchmark on device reads.
system	/sbin/hdparm /dev/hda	Shows hard disk configuration parameters.
system	bash	sh Extension.
system	bc	Is a text mode calculator.
system	chs	C shell.
system	dpkg -i package.deb	Installs package.deb (Debian).
system	if [ -x /path/to/dnetc ]; then echo "Starting Distributed.net Client..." /path/to/dnetc -quiet fi	The file /etc/rc.d/rc.local is like autoexec.bat from ms-dos and we cand add this lines on it. If it's not running, will start dnetc application.
system	ksh	Korn shell, combines sh and csh.
system	last	Show list of last logged in users (reads /var/log/wtmp).
system	ltrace elfexecutable	Traces an elf executable program (nice hacking tool)
system	nohup scriptname &	Runs scriptname in background and keeps running even if you close the window shell.
system	pdksh	ksh Extension.
system	rpm -e rpmname	Uninstalls rpm previous isntalled package (the rpmname must be obtained from rpm -qa and without .rpm).
system	rpm -qa |grep ftp	List current installed ftp servers.
system	rpm -qpl package.rpm	Shows what files are on the package.
system	rpm -Uvh package.rpm	Upgrades an installed package with the new one or installs it.
system	setterm -blank 0	Turns off console blank screensaver (that is On by default), you can put it on /etc/rc.local
system	sh	Changes to bash shell (Unix standard).
system	shutdown -h now	Shutdowns the computer. The same as halt
system	shutdown -r now	Reboots the computer. The same as reboot.
system	strace -s 200 executable	Intercepts system calls which are received by a process -s 200 is for string size 200 (nice hacking tools)
sytem	rpm -qi rpmname	Querys about version, complete description and more info for the package.
time	at 7:00 cdplayd	Sets the computer to play the cd at 7:00.
time	atq	Lists the automatic programmed jobs.
time	atrm 8	Deletes automatic job number 8.
time	date	Shows system date and time.
time	date -s "04/25/05" +"%D"	Changes sytem date to April, 25th 2005 .
time	date -s "15:00:00" +"%T"	Changes system time to 15:00.
time	Edit this file to memorize a job: etc/crontab	Ex: 00 00 20 10 * echo 'The winter is here' >/dev/null (this last command is to not send a mail to root). On the next directories you could copy applications or scripts that will run every time period. /etc/cron.hourly/ /etc/cron.daily/ /etc/cron.wee
time	rdate -p ntp.nasa.gov	Shows the server date and time.
time	rdate -s ntp.nasa.gov	Synchronizes your time and date with the server.
time	time application	Runs the application and when it's finished shows the running time.
time	uptime	Shows the total time since the computer was turned on.
users	/usr/bin/gpasswd -a user group	Asign that user to that group.
users	chmod mode file	Changes the file permissions
users	chown user:group file	Changes the file user and group owner.
users	gpasswd -d user group	To remove users from a group. The same is to edit: /etc/group
users	groups username	Shows groups that username is on
users	id username	Shows user identification and groups where he is on.
users	su	You become root until type: exit.
users	su -	Becomes root and reads root user's environment.
users	usermod -G group1,group2 user	Asign groups to a user.
X	setxkbmap	Try if your AltGr keys doesn't work on X mode.
X	switchdesk desktoptype	Changes the default desktop to anther (gnome, kde, wmaker, etc...).