Linux Commands

This article lists the most common commands and options for navigating and administering Linux distributions via the Command Line Interface (CLI) - usually called Terminal or Shell in the Linux environment.

Command Syntax

Linux commands are structured according to the following syntax

command [-options <parameter>] [<arguments>]

or

command [--option_long <parameter>] [<arguments>]

The command part calls a program that fulfils one or more functions. The ls command, for example, lists the contents of the folder in which the user is currently located.

As a rule, options can be used to give the program additional information on how it should behave. This can be the type or length of the output, but also the behavior in the event of errors or similar.

Both the command and the options can require additional parameters for the output. For example, if you want to move a folder, both the source and destination folders must be specified.

Example

We will look at the command:

ping -c 3 localhost

This command is structured as follows:

Command Part	Syntax	Description
ping	command name	The Ping package is called up
-c	option	The number of ping processes is specified
3	option parameter	3 ping processes are specified
localhost	command parameter	Destination address to be pinged

Auxiliary commands

Linux offers several ways to get help on commands and their options.

Command	Description
man	Stands for Manual and calls up the Manpage of a command
whatis	Also uses the man pages, but only gives a short summary of the command
info	Starts a utility program for displaying instructions for a command
apropos	To search for keywords within all manuals

Standard options

Linux programs also use some standard options that all packages listed there understand.

Option	Description
-h, --help	Displays all available options of the command and ends the process.
--version	Displays the version of the package and ends the process.
--	Limits the options. Options specified after a -- are interpreted as command parameters. The sort -- -r command would attempt to sort the -r file.

Commands

Listed here and organised by category are the most important commands for administering server systems. The tables also indicate whether the respective programs are included in a minimal installation of Debian Linux.

System

The following packages provide system information or allow certain system parameters to be manipulated.

Debian Standard	Command	Description	Important options	Option parameters	Option description	Arguments	Origin
✔	uname	Call up the name and information of the running kernel	-a, --all		Show all information		unix name
			-r, --kernel-release		Output release number of the kernel
			-v, --kernel-version		Output version of the kernel
✔	hostname	Retrieve or set the host name of the system	-I, --all-ip-adresses		Shows all network addresses of the host
			-f, --fqdn, --long		Displays the Fully Qualified Domain Name (FQDN)
			-s, --short		Displays the short name of the host
✔	uptime(siehe auch w)	Display the runtime (uptime) of the system (and logged-in users and utilization data)	-p, --pretty		Shortens the display to the pure uptime
✔	lscpu	Display information about the processor architecture	-a, --all		Displays all online and offline CPUs. May only be used together with -e or -p		list cpu
			-e, --extended	=listelement1,listelement2,... (possible list elements: CPU, CORE, SOCKET, BOOK, NODE, CACHE, ADDRESS, ONLINE, CONFIGURED, POLARIZATION)	Displays the list in human-readable format
			-p, --parse	=listelement1,listelement2,...(possible list elements as above)	Makes the output machine-readable
✔	lsblk	Displays information on selected or all block devices	-a, --all		Displays all devices		list block
			-f, --fs		Displays the file system
			-t, --tree		Displays the devices in a tree
✔	lsmod	List loaded kernel modules					list modules
✔	lsusb	List devices that are connected to the Universal Serial Bus (USB)	-v, --verbose		Show detailed information		list usb
			-t, --tree		Display output as a directory tree
✔	free	Display free and occupied memory	-h, --human		Makes the output human-readable. To do this, it is scaled to the smallest unit with three digits
			-s, --seconds		Indicates the free memory continuously after the specified time interval
			-c, --count		Specifies the number of time intervals after which the process is to be terminated
✔	df	Display hard disk usage	-h, --human-readable		Makes the output human-readable		disk free
			-t, --type	=TYPE	Lists only the specified file systems
			-T, --print-type		Outputs a column specifying the file system
✔	du	Displays the hard disk usage of files	-h, --human-readable		Makes the output human-readable		disk usage
			-c, --total		Create grand total
✔	modinfo	Shows information about specific Linux kernel modules				<modulname>	module information
✔	grep	Searches for patterns in files or system output and displays them	-f, -file=	<filename>	Searches a specific file for search patterns		global regular expression print
			-e,--regexp=	<Pattern>	Searches for a specific pattern
			-r,-recursive		Searches below each directory recursively

Process Management

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	top	Show all running processes					table of processes
✔	kill	Terminates a process	-L		Lists all signals that can be sent to a process	<Process ID (PID)>
✔	pkill	Sends a SIGTERM signal to the named process				<Process Name>	process kill
✔	killall	Terminates all processes by name				<Process Name>
✔	ps	Reports on the process status	-e		Selects all processes		process status
			-f		Displays the listing in full format
✘	bg	Commands jobs to be executed in the background1				<Job Title>	background
✘	fg	Commands jobs to be executed in the foreground				<Job Title>	foreground
✔	nice	Determines the priority of a command when allocating processor time				<Process Name>	nice
✔	renice	Changes the nice value of running processes				<nice value (-20[high] bis +19[low])> <Process-ID>

¹ If you want to start a job and have it run in the background, you can also add an & to the end of the command, e.g. ping 8.8.8.8 > pinglog &.

Directory Structure

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	mkdir	Creates new directories	-m, --mode	=MODE	Set access rights (see chmod)	<directory,directory,...>	make directory
✔	cd	Changes the current working directory				<directory>	change directory
✔	pwd	Outputs the current working directory					print working directory
✔	ls	Lists the contents of a directory	-l		Long list format		list
			-h, --human-readable		Human-readable format (bytes in KB, MB, GB)
			-a		Also lists hidden directories (directories beginning with .)

File Management

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	rm	Remove files and directories	-r		Recursive: Also deletes subdirectories	<file-/directoryname>	remove
			-f		Force: Forces deletion without user query
✔	touch	Change timestamp of files - Creates files if argument does not exist				<filename>
✔	cp	Copying files and directories				<sourcefile/-directory> <targetfile/-directory>	copy
✔	mv	Moving files and directories				<sourcefile/-directory> <targetfile/-directory>	move
✔	cat	Displaying and merging files				<filename>	concatenate
✔	head	Displaying the first lines of a file				<filename>
✔	tail	Displaying the last lines of a file				<filename>
✔	ln	Creating links between files				<filename>	link
✔	find	Finding files within a directory hierarchy				<filename>
✔	wc	Output bytes, words or lines of files	-l		Returns the number of lines in a file	<File>	word count

User and Group Administration

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	whoami	Output ID of the logged-in user
✔	who	Output ID of all logged in users
✘	finger	Outputs information on all logged-in users
✔	last	Display list of recently logged in users
✔	adduser	Adds a new user
✔	deluser	Deletes a user
✔	passwd	Allows the password to be changed					Password
✔	usermod	Change user accounts					user modification
✔	w	Displays information on all logged in users

Rights Management

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	chmod	Changes the mode of files					change mode
✔	chown	Changes the user and group rights					change owner
✔	chgrp	Changes the group membership of files					change group
✘	umask	Display or set the date mode mask	-S		Symbolic output		unix mask
			-p		Output in such a way that it can be reused as input

File Compression and Archiving

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	tar	Archiving tool					Tape Archive
✔	gzip	Data compression tool					GNU zip
✘	bzip2	Data compression tool					zipper
✘	xz	Data compression tool					x zip

I/O Redirection

Debian Standard	Command	Description	Important Options	Option Parameters	Option Description	Arguments	Origin
✔	<	Instead of a manual input, the content of a file is used as an argument (stdin)	grep -nw < /etc/protocols 'ipv6'
✔	>	The standard output ( stdout) is redirected to a file	echo "Hello World!" > text
✔	>>	The standard output (stdout) is appended to a file	echo "Hello World!" >> text
✔	2>	The error output ( stderr ) is redirected to a file	find /usr admin 2> error-file
✔	2>>	The error output (stderr) is appended to a file	find /usr games 2>> error-file
✔	&>	Redirects the standard output (stdout) and error output (stderr) to a file	find /usr admin &> searchfile
✔	&>>	Appends the standard output (stdout) and error output (stderr) to a file	find /usr games &>> searchfile
✔	|	The pipe links two commands together	cat /etc/protocols | grep 'ipv6'
✔	2>&1	Outputs the error output as standard output	cat notafile > file 2>&1

Miscellaneous and useful information

Command	Options	Arguments	Description
which		<Command>	Find a command
cat		/proc/cpuinfo	Display information about the processors in the system
cat		/proc/meminfo	Display information on the system's working memory
free	-h --si		Display information on the system's memory usage (-h for better readability with adapted units; h: human readable; --si: display in powers of 1000)
df	-H		Display of information on the system's data carrier allocations (-H for better readability with adapted units in powers of 1000)

Further information

Article on Linux kernel modules: How to display list of modules or device drivers in the Linux Kernel

References

Author: Stefan Bohn Stefan Bohn has been employed at Thomas-Krenn.AG since 2020. Originally based in PreSales as a consultant for IT solutions, he moved to Product Management in 2022. There he dedicates himself to knowledge transfer and also drives the Thomas-Krenn Wiki.