Linux/Basic commands

Unix-like operating systems require a working knowledge of several basic commands. Unix®, Linux, BSD and such use a ubiquitous set of these based on the Single UNIX Specification and other standards. Learning to operate a command line interface is a key skill in learning Linux and BSD.

Commands where mistyping could have inconvenient consequences should be drafted in a text editor first and then pasted into terminal, or after a # hash character for temporarily marking the text of the command as a non-executable comment, which is then removed after typing the correct command. Terminal emulators may support marking commands as comment in history through Ctrl+Alt+#.

Basic commands

IEEE Std 1003.1-2001 utilities

Name	Category	Description	First appeared
admin	SCCS	Create and administer SCCS files
alias	Misc	Define or display aliases
ar	Misc	Create and maintain library archives
asa	Text Processing	Interpret carriage-control characters
at	Process Management	Execute commands at a later time	Version 7 AT&T UNIX
awk	Text processing	Pattern scanning and processing language	Version 7 AT&T UNIX
basename	Filesystem	Return non-directory portion of a pathname
bash	Shell	The Bourne-again shell
batch	Process Management	Schedule commands to be executed in a batch queue
bc	Misc	Arbitrary-precision arithmetic language
bg	Process Management	Run jobs in the background
break	Shell programming	Exit from for, while, or until loop
c99	C Programming	Compile standard C programs
cal	Misc	Print a calendar	Version 5 AT&T UNIX
cat	Filesystem	Concatenate and print files	Version 1 AT&T UNIX
cd	Filesystem	Change the working directory
cflow	C Programming	Generate a C-language flowgraph
chgrp	Filesystem	Change the file group ownership
chmod	Filesystem	Change the file modes/attributes/permissions	Version 1 AT&T UNIX
chown	Filesystem	Change the file ownership	Version 1 AT&T UNIX
chroot	Processes	run a command or interactive shell using a specific directory as the root directory	Prior to 4.2BSD
cksum	Filesystem	Write file checksums and sizes	4.4BSD
cmp	Filesystem	Compare two files	Version 1 AT&T UNIX
comm	Text Processing	Select or reject lines common to two files	Version 4 AT&T UNIX
command	Shell Programming	Execute a simple command
compress	Filesystem	Compress data	4.3BSD
continue	Shell programming	Continue for, while, or until loop
cp	Filesystem	Copy files	Version 1 AT&T UNIX
crontab	Misc	Schedule periodic background work
csplit	Text Processing	Split files based on context	PWB UNIX
ctags	C Programming	Create a tags file	3.0BSD
cut	Shell Programming	Cut out selected fields of each line of a file
cxref	C Programming	Generate a C-language program cross-reference table
date	Misc	Write the date and time	Version 1 AT&T UNIX
dd	Filesystem	Convert and copy a file
delta	SCCS	Make a delta (change) to an SCCS file
df	Filesystem	Report free disk space	Version 1 AT&T UNIX
diff	Text processing	Compare two files
dirname	Filesystem	Return the directory portion of a pathname
dot	Shell programming	Execute commands in the current environment
du	Filesystem	Estimate file space usage	Version 1 AT&T UNIX
echo	Shell programming	Write arguments to standard output
ed	Text processing	The standard text editor	Version 1 AT&T UNIX
env	Misc	list environment variables or invoke a command in a modified environment
eval	Shell programming	Construct command by concatenating arguments
ex	Text processing	Text editor	BSD
exec	Shell programming	Execute commands and open, close, or copy file descriptors
exit	Shell programming	Cause the shell to exit
expand	Text Processing	Convert tabs to spaces	3.0BSD
export	Misc	Set the export attribute for variables
expr	Shell Programming	Evaluate arguments as an expression
false	Shell programming	Return false value
fc	Misc	Process the command history list
fg	Process Management	Run jobs in the foreground
file	Filesystem	Determine file type	Version 4 AT&T UNIX
find	Filesystem	Find files	Version 1 AT&T UNIX
flex	C Programming	Generate programs for lexical tasks
fold	Text processing	Filter for folding lines
fort77	C Programming	w:FORTRAN compiler
fortune	Misc	Displays a random quotation
ftp	Internet	Internet file transfer program
fuser	Process Management	List process IDs of all processes that have one or more files open
gawk	Text processing	Pattern scanning and processing language, GNU's version of awk
gencat	Misc	Generate a formatted message catalog
get	SCCS	Get a version of an SCCS file
getconf	Misc	Get configuration values
getopts	Shell Programming	Parse utility options
grep	Misc	Search text for a pattern
groups	Misc	List groups a user belongs to
hash	Misc	Remember or report utility locations
head	Text processing	Copy the first part of files	PWB UNIX
hostname	Networking	Show the system's host name
iconv	Text processing	Codeset conversion
id	Misc	Return user identity	4.4BSD
iostat	Input/Output information	collect and show operating system storage input and output statistics
ipcrm	Misc	Remove a message queue, semaphore set, or shared memory segment identifier
ipcs	Misc	Report interprocess communication facilities status
jobs	Process Management	Display status of jobs in the current session
join	Text Processing	Relational database operator
kill	Process Management	Terminate or signal processes	Version 3 AT&T UNIX
less	Text processing	Display files on a page-by-page basis
lex	C Programming	Generate programs for lexical tasks
link	Filesystem	Call link function	Version 1 AT&T UNIX
ln	Filesystem	Link files	Version 1 AT&T UNIX
locale	Misc	Get locale-specific information
localedef	Misc	Define locale environment
logger	Shell programming	Log messages
login	Misc	Begin sessions on a system
logname	Misc	Return the user's login name	4.4BSD
logout	Misc	End sessions on a system
lp	Text Processing	Send files to a printer
ls	Filesystem	List directory contents	Version 1 AT&T UNIX
m4	Misc	Macro processor	PWB UNIX
mailx	Misc	Process messages	Version 1 AT&T UNIX
make	Programming	Maintain, update, and regenerate groups of programs
man	Misc	Display system documentation
mesg	Misc	Permit or deny messages	Version 1 AT&T UNIX
mkdir	Filesystem	Make directories	Version 1 AT&T UNIX
mkfifo	Filesystem	Make FIFO special files	4.4BSD
mktemp	Filesystem	Create a temporary file or directory
more	Text processing	Display files on a page-by-page basis
mount	Filesystem	Mount a file system
mv	Filesystem	Move files	Version 1 AT&T UNIX
nano	Text Programming	Small text editor
netstat	Networking	Displays network information and statistics
newgrp	Misc	Change to a new group	Version 6 AT&T UNIX
nice	Process Management	Invoke a utility with an altered nice value	Version 4 AT&T UNIX
nl	Text Processing	Line numbering filter
nm	C Programming	Write the name list of an object file
nohup	Process Management	Invoke a utility immune to hangups
od	Misc	Dump files in various formats	Version 1 AT&T UNIX
passwd	System	Set or change user password
paste	Text processing	Merge corresponding or subsequent lines of files	Version 32V AT&T UNIX
patch	Text processing	Apply changes to files
pathchk	Filesystem	Check pathnames
pax	Misc	Portable archive interchange	4.4BSD
pgrep	Process Management	Find processes with the given name using pattern matching
pkill	Process Management	Kills processes with the given name using pattern matching
pr	Text processing	Print files	Version 1 AT&T UNIX
printf	Shell programming	Write formatted output	4.3BSD-Reno
prs	SCCS	Print an SCCS file
ps	Process Management	Report process status	Version 4 AT&T UNIX
pstree	Process Management	Display a tree of processes
pwd	Filesystem	print working directory - Return working directory name
qalter	Batch Utilities	Alter batch job
qdel	Batch Utilities	Delete batch jobs
qhold	Batch Utilities	Hold batch jobs
qmove	Batch Utilities	Move batch jobs
qmsg	Batch Utilities	Send message to batch jobs
qrerun	Batch Utilities	Rerun batch jobs
qrls	Batch Utilities	Release batch jobs
qselect	Batch Utilities	Select batch jobs
qsig	Batch Utilities	Signal batch jobs
qstat	Batch Utilities	Show status of batch jobs
qsub	Batch Utilities	Submit a script
read	Shell Programming	Read a line from standard input
readonly	Misc	Set the readonly attribute for variables
renice	Process Management	Set nice values of running processes	4.0BSD
return	Shell Programming	Return from a function
rm	Filesystem	Remove files or directories	Version 1 AT&T UNIX
rmdel	SCCS	Remove a delta from an SCCS file
rmdir	Filesystem	Remove directories	Version 1 AT&T UNIX
sact	SCCS	Print current SCCS file-editing activity
sar	System Administration	System Activity Report	Report System Activity
sccs	SCCS	Front end for the SCCS subsystem
sed	Text processing	Stream editor	Version 7 AT&T UNIX
seq	Misc	Print a sequence of numbers
set	Misc	Set or unset options and positional parameters
sh	Shell programming	Shell, the standard command language interpreter	Version 7 AT&T UNIX
shift	Shell programming	Shift positional parameters
shopt	Shell programing	Control optional shell behavior
sleep	Shell programming	Suspend execution for an interval	Version 4 AT&T UNIX
sort	Text Processing	Sort, merge, or sequence check text files
split	Misc	Split files into pieces	Version 3 AT&T UNIX
strings	C Programming	Find printable strings in files
strip	C Programming	Remove unnecessary information from executable files
stty	Misc	Set the options for a terminal
suspend	Shell programming	Suspend execution of the shell until it receives a continue signal
tabs	Misc	Set terminal tabs	PWB UNIX
tail	Text processing	Copy the last part of a file	PWB UNIX
talk	Misc	Talk to another user	4.2BSD
tee	Shell programming	Duplicate standard input
test	Shell programming	Evaluate expression
time	Process Management	Time a simple command	Version 3 AT&T UNIX
times	Process Management	Write process times
touch	Filesystem	Create file and Change file access and modification times	Version 7 AT&T UNIX
top	Process Management	Real-time display of running processes
tput	Misc	Change terminal characteristics	System V
tr	Text processing	Translate characters	Version 4 AT&T UNIX
trap	Process Management	Trap signals
true	Shell programming	Return true value
tsort	Text processing	Topological sort	Version 7 AT&T UNIX
tty	Misc	Return user's terminal name	Version 1 AT&T UNIX
type	Misc	Displays how a name would be interpreted if used as a command
ulimit	Misc	Set or report file size limit
umask	Misc	Get or set the file mode creation mask
umount	Filesystem	Unmount a filesystem
unalias	Misc	Remove alias definitions
uname	Misc	Return system name	PWB UNIX
uncompress	Misc	Expand compressed data	4.3BSD
unexpand	Text Processing	Convert spaces to tabs	3.0BSD
unget	SCCS	Undo a previous get of an SCCS file
uniq	Text Processing	Report or filter out repeated lines in a file	Version 3 AT&T UNIX
unlink	Filesystem	Call the unlink function	Version 1 AT&T UNIX
unset	Misc	Unset values and attributes of variables and functions
uucp	Network	System-to-system copy
uudecode	Network	Decode a binary file	4.0BSD
uuencode	Network	Encode a binary file	4.0BSD
uustat	Network	uucp status inquiry and job control
uux	Process Management	Remote command execution
val	SCCS	Validate SCCS files
vi	Text processing	Screen-oriented (visual) display editor	BSD
wait	Process Management	Await process completion
wc	Text processing	Word, line, and byte or character count	Version 1 AT&T UNIX
what	SCCS	Identify SCCS files
who	System Administration	Display who is on the system	Version 1 AT&T UNIX
write	Misc	Write to another user's terminal	Version 1 AT&T UNIX
xargs	Shell Programming	Construct argument lists and invoke utility	PWB UNIX
yacc	C Programming	Yet another compiler compiler	PWB UNIX
zcat	Text Processing	Expand and concatenate data

Unix-like

Like RMS says, "GNU means GNU's Not Unix". Only Unix® is really Unix. Linux and the BSDs are definitely Unix-like though neither one is compliant with the above-mentioned "official" specification. What we present here is based on a set of tools that have been around for a long time. We will be looking at generalizations that behave in similar ways in most *nix environments.

BusyBox

BusyBox is a good example of a more basic collection of utilities and are well suited to the novice. They can be found in Mini Linux distributions, such as Tiny Core Linux.

Exercise 1 Go to TinyCoreLinux.com and check it out.

GNU Core Utilities

The GNU Core Utilities are much more extensive and not for the faint at heart. They are found on most full-sized BSD and Linux systems in their full glory.

Command line arguments

This section lists arbitrary commands that could be useful. Feel free to add any commands you found useful but are not sure where else to add. Some of these commands may require root access ("sudo").

Devices with example numbers are specified in these examples.

Action	Command(s)
List devices of the class "disk" with model number	lshw -short -class disk
Details about a specific device (e.g. /dev/sr0)	udisksctl info -b /dev/sr0
Spin down hard disk or optical disc drive	hdparm -y /deb/sdb sdparm --readonly --command=stop /dev/sr0
Write caching It improves performance but could lose data if a device is physically disconnected shortly after a file transfer without safe unmounting.	(replace "X" with the correct device name) Deactivate: hdparm -W 0 /dev/sdX Activate: hdparm -W 1 /dev/sdX See status: hdparm -i /dev/sdX
Eject optical disc tray	eject /deb/sr0 sdparm --readonly --command=eject /dev/sr0
Close optical disc tray	eject -t /dev/sr3 sdparm --readonly --command=load /dev/sr3
Get size of block device	blockdev --getsz /dev/[device]

Other useful commands

• datamash
• mtail
• parallel
• rsync advanced copy and synchronization tool including progress indicator
• sed stream editor for filtering and transforming text
• stress (command): stress --cpu 4
• sudo
• tr
• ts adds a timestamp to the beginning of each line of input
• ls – list files
• uptime – time since last booting
• du – disk usage of files and directories
• df – total disk usage
• readlink: readlink -f [file path] generates an absolute (full) file path
• stat – advanced details about a file like multiple date/time stamps, size, inode count, and access rights.
• losetup – loop device utility
• blockdev – shows information and allows configuring data storage devices, such as read-only mode using blockdev --setro.

External links

• SS64.com: Command line reference
• djangstorm.com: Linux Commands Collection