Appendix B: BASH Command Index

This appendix provides a whistle-stop tour of commands that can be used at the BASH shell. This is a highly selective listing, which is to say it is a guide to commands that see day-to-day use on average desktop systems. In a similar fashion, although some command options are listed, they’re strictly limited to those that receive regular deployment.

The descriptions of each command are deliberately simple. It’s important to note that the quantity of space a command is given is not an indication of its importance or usefulness. To this end, commands in the list with an asterisk after their name offer far more than the brief description here hints at. In such cases, I strongly advise you to refer to the command’s man page for more information.

Various conventions are used in the list:

• Italics: You should substitute your own details wherever italicized words appear.

• $: Commands that can and might be run by ordinary users are preceded with a dollar sign ($).

• #: Commands that require root privileges, or that are ordinarily run by root, are preceded with a hash (#).

Commands that present dangers to the system through misuse are clearly marked. Such commands should not be used without research into the command’s usage and function.

Command	Notes/Command Options	Example of Typical Use
$ alias	Create or display command aliases	alias list='l'
$ apropos	Search man pages for specified words/phrases	apropos "word or phrase"
$ bzip2	Compress specified file (replaces original file with compressed file and gives it .bz2 file extension) -d: Decompress specified file -k: Don’t delete original file -t: Test; do a dry run without writing any data	bzip2 myfile
$ bzip2recover	Attempt recovery of specified damaged .bz2 file	bzip2recover myfile.tar.bz2
$ cal	Display calendar for current month (or specified month/year)	cal 4 2005
$ cat	Display a file on screen or combine and display two files together	cat myfile
$ cd	Change to specified directory	cd /usr/bin
$ cdparanoia *	Convert CD audio tracks to hard disk files -B: Batch mode; convert all tracks to individual files -S: Set CD read speed (2, 4, 8, 12, and so on; values relate to CD-drive spin speed; used to avoid read errors)	cdparanoia –S 8 –B
# cdrecord *	Burn audio or CD-R/RW data discs (the latter usually based on an ISO image; see mkisofs) -dev=: Specify the drive’s device number (can be discovered by running cdrecord with the --scanbus option) --scanbus: Scan to see which CD-R/RW drives are present and return device numbers	cdrecord dev=0,0,0 –speed=16 -v myfile.iso
-speed=:	Specify the write speed (2, 4, 6, 8, and so on) -v: Verbose output; obligatory for feedback on cdrecord's progress
# cfdisk *	DANGEROUS! Menu-based disk-partitioning program	cfdisk /dev/hda
# chgrp	Change group ownership of a file/directory -R: Recursive; apply changes to subdirectories	chgroup mygroup myfile
# chkconfig	Administer or display services that comprise current run level	chkconfig servicename on
$ chmod	Change permissions of a file/directory (where a=all, u=user, g=group, r=read, w=write, x=executable) -R: Recursive; apply to subdirectories --reference=: Copy permissions from specified file	chmod a+rw myfile
$ chown	Change file ownership to specified username -R: Recursive; apply to subdirectories	chown username myfile1
# chroot	Change the root of the file system to the specified path	chroot /home/mydirectory
# chvt	Switch to the specified virtual terminal (equivalent of holding down Ctrl+Alt and pressing F1–F6)	chvt 3
$ clear	Clears terminal screen and places cursor at top	clear
$ cp	Copy files -r: Recursive; copy subdirectories and the files therein -s: Create symbolic link instead of copying	cp myfile1 directory/
$ crontab	Edit or display the user’s crontab file (scheduled tasks) -e: Edit the crontab file (create/amend) -l: List crontab entries -r: Delete the crontab file -u: Specify a user and edit their crontab file	crontab -e
$ date	Display the date and time	date
$ df	Display free disk space within file system -h: Human readable; display sizes in KB, MB, GB, and TB, as appropriate -l: Restrict to local file systems, as opposed to network mounts	df -h
$ diff	Display differences between specified files -a: Consider all files text files (i.e. don’t halt when asked to compare binary files) -i: ignore lowercase and uppercase differences	diff myfile1 myfile2
$ diff3	Display differences between three specified files	diff3 myfile1 myfile2 myfile3
$ dig	Look up IP address of specified domain	dig mysite.com
# dmesg	Display kernel message log	dmesg
# dosfsck *	Check and repair MS-DOS–based file hard disk partition (see also fsck) -a: Repair without asking user for confirmation -r: Repair file system asking user for confirmation when two or more repair methods are possible -v: Verbose; display more information	dosfsck -rv /dev/hda4
$ du	Show sizes of files and folders in kilobytes -h: Human readable; produce output in MB, GB, and TB -s: Summary; display totals only for directories rather than for individual files	du -h /home/myuser
$ eject	Eject a removable storage disk -t: Close an already open tray	eject /media/dvd-rom
$ emacs *	Start the emacs text editor program	emacs myfile
$ ex *	Start a simple text-editor program used principally within shell scripts	ex myfile.txt
$ exit	Log out of shell (end session)	exit
$ fdformat	Low-level format a floppy disk (this won’t create a file system; see also mkfs)	fdformat /dev/fd0
# fdisk *	DANGEROUS! Hard-disk partitioning program -l: List partition table	fdisk /dev/hda
$ fg	Brings job running in background to foreground	fg 1
$ file	Display information about specified file, such as its type	file myfile
$ find *	Find files by searching directories (starting in current directory) -maxdepth: Specify the number of subdirectories levels to delve into, starting from 1 (current directory) -name: Specify name of file to search for -type: Specify file types to be returned; -type d returns directories and -type f returns only files	find -name "myfile"
$ findsmb	Search network for Windows file sharing (SMB) computers	findsmb
$ free	Display information about memory usage -m: Show figures in MB -t: Total the columns at bottom of table	free -m
# fsck *	Check file system for errors (usually run from rescue disc)	fsck /dev/hda1
$ ftp *	FTP program for uploading/downloading to remote sites	ftp ftp.mysite.com
$ fuser	Show which processes are using a particular file or file system -v: Verbose; detailed output	fuser -v myfile
$ grep *	Search specified file for specified text string (or word) -i: Ignore uppercase and lowercase differences -r: Recursive; delve into subdirectories (if applicable) -s: Suppress error messages about inaccessible files, etc.	grep "phrase I want to find" myfile.txt
# groupadd	Create new group	groupadd mygroup
# groupdel	Delete specified group	groupdel mygroup
$ groups	Display groups the specified user belongs to	groups myuser
$ gzip	Compress files and replace original file with compressed version -d: Decompress specified file -v: Verbose; display degree of compression	gzip myfile
# halt	Initiate shutdown procedure, ending all processes and unmounting all disks -p: Power off system at end of shutdown procedure	halt -p
# hdparm *	DANGEROUS! Tweak hard disk settings	hdparm /dev/hda
$ head	Print topmost lines of text files (default is first 10 lines) -n: Specify number of lines (such as -n 5)	head myfile.txt
$ help	Display list of common BASH commands	help
$ history	Display history file (a list of recently used commands)	history
$ host	Query DNS server based on specified domain name or IP address -d: Verbose; return more information -r: Force name server to return its cached information rather than query other authoritative servers	host 65.19.150.100
$ hostname	Display localhost-style name of computer	hostname
$ id	Display username and group info of specified user (or current user if none specified)	id myuser
Command	Notes/Command Options	Example of Typical Use
# ifconfig *	Display or configure settings of a network interface (assign an IP address, subnet mask, and activate/deactivate it) down: Disable interface (used at end of command chain) netmask: Specify a subnet mask up: Enable interface (used at end of command chain)	ifconfig eth0 192.168.0.10 netmask 255.255.0.0 up
$ info *	Display info page for specified command	info command
# init	Change current run level	init 3
$ ispell *	Program that spellchecks specified file -b: Back up original file (provided original file is altered and subsequently saved)	ispell myfile.txt
$ jobs	Display list of jobs running in background	jobs
# kernelversion	Display kernel version number	kernelversion
$ kill	Kill specified process	kill 1433
$ killall	Kill process(es) that have specified name(s) -i: Confirm before killing process -v: Verbose; report if and when successful	killall processnumber
$ last	Display details of recent logins, reboots, and shutdowns	last
$ ldd	Display system files (libraries) required by specified program	ldd /usr/bin/program
$ less	Interactively scroll through a text file -q: Quiet; disable beeps when end of file is reached or other error encountered -i: Ignore case; make all searches case-insensitive unless uppercase letters are used	less myfile.txt
$ ln	Create links to specified files, such as symbolic links -s: Create symbolic link (default is hard link)	ln -s myfile1 mfile2
$ look	Spell-check specified word (or part of word) -f: Ignore uppercase and lowercase	look word
$ lpr	Print file (send it to the printer spool/queue) -V: Verbose; print information about progress of print job	lpr myfile.txt
$ lpstat	Display print queue	lpstat
$ ls	List directory -a: List all files, including hidden files -d: List only directory names rather than their contents -h: Human readable; print figures in KB, MB, GB, and TB -l: Long list; include all details, such as file permissions -m: Show as comma-separated list	ls -h mydirectory
# lsmod	Display currently loaded kernel modules	lsmod
$ lsof	Display any files currently in use -u: Limit results to files used by specified user	lsof -u username
$ mail *	Program that can send and also receive mail -s: Specify subject prior to creating new mail	mail [e-mail]
$ man	Display specified command’s manual	man command
$ mc *	Semigraphical file-browsing program based on Norton Commander	mc
$ md5sum	Display MD5 checksum (normally used to confirm a file’s integrity after download)	md5sum myfile
# mkfs *	DANGEROUS! Create specified file system on specified device (such as a floppy disk) -t: Specify type of file system	mkfs -t vfat /dev/fd0
$ mkisofs *	Create ISO image file from specified directory (usually for burning to disc with cdrecord) -o: Options; this must appear after command to indicate that command options follow -apple: Use Mac OS extensions to make ensuing disc readable on Apple computers -f: Follow symbolic links and source actual files -J: Use Joliet extensions (make ISO compatible with Windows) -R: Use Rock Ridge extensions (preferred Linux CD-ROM file system) -v: Verbose; display more information (-vv for even more info)	mkisofs -o isoimage.iso -R -J -v mydirectory
# modinfo	Display information about kernel module	modinfo modulename
# modprobe	Insert specified module into the kernel, as well as any others it relies on -k: Set module’s autoclean flag so it will be removed from memory after inactivity -r: Remove specified module as well as any it relies on to operate	modprobe modulename
$ more	Interactively scroll through text file (similar to less)	more myfile.txt
# mount *	Mount specified file system at specified location -o: Specify command options, such as rw to allow read/write access; various types of file systems have unique commands	mount /dev/hda4 /mnt
$ mv	Move (or rename) specified files and/or directories -b: Back up files before moving -v: Display details of actions carried out	mv myfile mydirectory/
$ netstat *	Show current network connections	netstat -a
$ nice	Run specified command with specified priority -n: Specify priority, ranging from the highest priority of -20, to 19, which is the lowest priority	nice -n 19
$ nohup	Run specified command and continue to run it, even if user logs out	nohup command
$ passwd	Change user’s password	passwd
$ ping	Check network connectivity between local machine and specified address -w: Exit after specified number of seconds (such as -w 5)	ping mydomain.com
$ printenv	Display all environment variables for current user	printenv
$ ps *	Display currently running processes a: List all processes (note that command options don’t require preceding dash) f: Display ownership of processes using tree-style graphics u: Limit results to processes running for and started by current user x: Include processes in results not started by user but running with the user ID	ps aux
$ pwd	Display current directory	pwd
# reboot	Reboot computer	reboot
$ renice	Change a process’ priority while it’s running (see nice)	renice 19 10704
$ rm	Delete single or multiple files and/or directories -r: Recursive; delete specified directories and any subdirectories -f: Force; don’t prompt for confirmation before deleting (use with care!)	rm -rf mydirectory
# rmmod	Delete module from kernel	rmmod modulename
# route *	Add and create (or view) entries in routing table (see ifconfig)	route add default gw 192.168.1.1
# rpm *	Red Hat Package Manager; installs specified RPM package(s) -e: Uninstall specified package -h: Graphically indicate progress when installing/upgrading -i: Install package --nodeps: Ignore dependency errors (use with care!) -qa: Display listing of installed packages -qp: Display details of specified package -U: Upgrade package (will install if package not already installed) -v: Verbose; display detailed output	rpm -Uvh packagename
# runlevel	Display current run level	runlevel
# sax2 *	Configure X (keyboard, mouse, and display); note that this is a SUSE Linux-specific GUI tool -V: Specify initial resolution and refresh rate (such as -V 800x600@60)	sax2
$ screen *	Program that runs pseudo shell that is kept alive regardless of current user login -ls: Display list of currently running screen sessions -R: Reattach to already running screen session or start new one if none available	screen
$ sftp *	Secure Shell FTP; like FTP but running over an ssh connection (see below)	sftp username@192.168.1.14
$ shred	Overwrite data in a file with gibberish, thereby making it irrecoverable -u: Delete file in addition to overwriting -v:Verbose; show details of procedure -f: Force permissions to allow writing if necessary	shred -fv myfile
$ sleep	Pause input for the specified period of time (where s=seconds, m=minutes, h=hours, d=days)	sleep 10m
$ smbclient *	FTP-style program with which you can log in to a SMB (Windows)-based file share	smbclient //192.168.1.1/
$ sort	Sort entries in the specified text file (default is ASCII sort)	sort myfile.txt -o sorted.txt
$ ssh *	Log in to remote computer using secure shell	ssh username@192.168.1.15
$ startx	Start GUI session when in run level 3 (at shell login)	startx
$ su	Temporarily log in as specified user; log in as root if no user specified -: Adopt user’s environment variables, such as $PATH	su -
$ sudo	Execute specified command with root privileges (provided the facility has been set up)	sudo command
# SuSEconfig	Update system according to settings in SuSE Linux-specific config files	SuSEconfig
$ tac	Display specified text file but in reverse (from last to first line)	tac myfile.txt
$ tail	Display final lines of specified text file -n: Specify number of lines to display (such as -n4)	tail myfile.txt
$ tar *	Combine specified files and/or directories into one larger file, or extract from such a file -c: Create new archive -j: Use bzip2 in order to compress (or decompress) files -f: Specifies filename (must be last in chain of command options) -r: Add files to existing archive -x: Extract files from existing archive -z: Use gzip to compress (or decompress) files	tar -zcf myfile.tar.gz mydirectory
$ tee	Display piped output and also save it to specified file	ls -lh| tee listing.txt
$ top *	Program that both displays and lets the user manipulate processes	top
$ touch	Give specified file current time and date stamp; if it doesn’t exist, create a zero-byte file with that name	touch myfile
# traceroute	Discover and display network path to another host	traceroute 192.168.1.20
$ umask	Set default permissions assigned to newly created files	umask u=rwx,g=r,o=
# umount	Unmount a file system	umount /media/cdrom
# useradd	Add new user -m: Create home directory for user	useradd -m username
# userdel	Delete all mention of user in system configuration files (effectively deleting the user, although files owned by him/her might remain) -r: Remove user’s home directory	userdel -r username
$ unalias	Remove specified alias -a: Remove all aliases (use with care!)	unalias command
$ uname	Display technical information about current system -a: Display all basic information	uname -a
$ unzip	Unzip a Windows-compatible Zip file -l: Display archive content but don’t actually unzip	unzip myfile.zip
$ uptime	Display uptime for system, as well as CPU load average and logged-in users	uptime
$ vi *	Text editor program	vi
$ wc	Count the number of words in a file	wc myfile.txt
$ whatis	Display one-line summary of specified command	whatis command
$ whereis	Display information on where a binary command is located, along with its source code and man page (if applicable) -b: Return information only about binary programs	whereis -b command
# xf86config *	Command-line program that configures X system, including mouse, keyboard, and display	xf86config
$ xhost	Configure which users/systems can run programs on the X server +: When followed by a username and/or system name, gives the user/system permission to run programs on the X server; when used on its own, lets any user/system use the X server -: Opposite of above	xhost +
$ xinit	Start elementary GUI session (when in run level 3)	xinit
# yast2 *	Start the YaST2 program -i: Install specified RPM	yast2
$ zip	Create Windows-compatible compressed Zip files -r: Recursive; includes all subdirectories and files therein -u: Updates Zip with specified file -P: Encrypts Zip with specified password -v: Verbose; display more information -#: Set compression level (from 0, which is no compression, to 9, which is highest)	zip -r myfile.zip mydirectory
$ zipgrep	Searches inside Zip files for specified text string	zipgrep "search phrase" myfile.zip