A Linux system administrator needs to know some Linux tricks. In this article, you will learn A to Z Linux commands overview with examples.
There are a countless number of commands in Linux. You are bound to use a number of them on a daily routine or numerous times to perform common tasks than others. It is important to note that certain commands are “distro-based” – they can only be found in specific distros. While others are generic Unix/Linux commands that you’ll find in all if not most mainstream distros. To let this guide work better, try to purchase and use VPS or Linux web hosting.
A to Z Linux commands overview with examples
In this article, we will introduce you, the list of most frequently used Linux commands with their examples for easy learning. So join us to learn A to Z Linux commands overview with examples.
First, you can find the actual description of each Linux command on their manual page which you can access like this:
The adduser and addgroup commands are used to add a user and group to the system respectively according to the default configuration specified in /etc/adduser.conf file.
sudo adduser eldernode
To know about agetty, it is a program that manages physical or virtual terminals and is invoked by init. Once it detects a connection, it opens a tty port, asks for a user’s login name, and calls up the /bin/login command. Agetty is a substitute of Linux getty:
agetty -L 9600 ttyS1 vt100
And alias. which is a useful shell built-in command for creating aliases (shortcut) to a Linux command on a system. It is helpful for creating new/custom commands from existing Shell/Linux commands (including options):
alias home='cd /home/eldernode/public_html'
By running the above command, you will create an alias called home for /home/eldernode/public_html directory, so whenever you type home in the terminal prompt, it will put you in the /home/eldernode/public_html directory.
anacron is a Linux facility used to run commands periodically with a frequency defined in days, weeks, and months.
Unlike its sister cron; it assumes that a system will not run continuously, therefore if a scheduled job is due when the system is off, it’s run once the machine is powered on.
In the following, you can see the apropos command is used to search and display a short man page description of a command/program as follows.
apt tool is a relatively new higher-level package manager for Debian/Ubuntu systems:
sudo apt update
apt-get is a powerful and free front-end package manager for Debian/Ubuntu systems. So, where can you use it? to install new software packages, remove available software packages, upgrade existing software packages as well as upgrade the entire operating system.
sudo apt-get update
aptitude is a powerful text-based interface to the Debian GNU/Linux package management system. Like apt-get and apt; it can be used to install, remove, or upgrade software packages on a system.
sudo aptitude update
arch is a simple command for displaying machine architecture or hardware name (similar to uname -m):
ARP (Address Resolution Protocol) is a protocol that maps IP network addresses of a network neighbor with the hardware (MAC) addresses in an IPv4 network.
Use it when you need to find all alive hosts on a network.
sudo arp-scan --interface=enp2s0 --localnet
at command is used to schedule tasks to run in a future time. It’s an alternative to cron and anacron, however, it runs a task once at a given future time without editing any config files:
For example, to shut down the system at 22:10 today, run:
sudo echo "shutdown -h now" | at -m 22:10
atq command is used to view jobs in at command queue:
atrm command is used to remove/deletes jobs from at command queue:
You can use the Awk as a powerful programming language that is created for text processing and generally used as data extraction and reporting tool.
Similar to the at command, batch is also used to schedule tasks to run a future time.
basename command helps to print the name of a file stripping of directories in the absolute path:
And, bc is a simple yet powerful and arbitrary precision CLI calculator language which can be used like this:
echo 20.05 + 15.00 | bc
You will use the bg command to send a process to the background.
tar -czf home.tar.gz . bg jobs
bzip2 command is used to compress or decompress file(s).
bzip2 -z filename Compress bzip2 -d filename.bz2 Decompress
To print a calendar on the standard output, use the cal command.
cat command is used to view contents of a file or concatenate files, or data provided on standard input, and display it on the standard output.
Use the chgrp command to change the group ownership of a file. Provide the new group name as its first argument and the name of the file as the second argument like this:
chgrp eldernode users.txt
chmod command is used to change/update file access permissions like this.
chmod +x sysinfo.sh
chown command changes/updates the user and group ownership of a file/directory like this.
chmod -R www-data:www-data /var/www/html
You may use the cksum command to display the CRC checksum and byte count of an input file.
If you wish to be able to clear the terminal screen by a command, simply type the clear command.
cmp is ready to perform a byte-by-byte comparison of two files for you.
cmp file1 file2
comm command is used to compare two sorted files line-by-line as shown below.
comm file1 file2
cp command is used for copying files and directories from one location to another.
cp /home/eldernode/file1 /home/eldernode/Personal/
To displays/set the system date and time date, you can use the date command.
date date --set="8 JUN 2017 13:00:00"
dd command is used for copying files, converting and formatting according to flags provided on the command line. It can strip headers, extracting parts of binary files, and so on.
Verify creating a bootable USB device in the example below.
dd if=/home/eldernode/kali-linux-1.0.4-i386.iso of=/dev/sdc1 bs=512M; sync
df command is used to show file system disk space usage as follows.
diff command is used to compare two files line by line. It can also be used to find the difference between two directories in Linux as below.
diff file1 file2
dir command works like Linux ls command, it lists the contents of a directory.
dmidecode command is a tool for retrieving hardware information of any Linux system. It-dumps a computer’s DMI (a.k.a SMBIOS) table contents in a human-readable format for easy retrieval.
To view your system hardware info, you can type:
sudo dmidecode --type system
du command is used to show disk space usage of files present in a directory as well as its sub-directories as follows.
echo command prints a text of line provided to it.
echo “This is Eldernode - Linux How Tos”
eject command is used to eject removable media such as DVD/CD ROM or floppy disk from the system.
eject /dev/cdrom eject /mnt/cdrom/ eject /dev/sda
env command lists all the current environment variables and used to set them as well.
To exit a shell, choose the exit command
expr command is used to calculate an expression as shown below.
expr 20 + 30
Also to show the prime factors of a number, use the factor command.
find command lets you search for files in a directory as well as its sub-directories. It searches for files by attributes such as permissions, users, groups, file type, date, size, and other possible criteria.
find /home/eldernode/ -name eldernode.txt
free command shows the system memory usage (free, used, swapped, cached, etc.) in the system including swap space. Use the -h option to display output in a human-friendly format.
To search for a specified pattern in a file (or files) and displays in output lines containing that pattern, use the grep command.
grep ‘eldernode’ domain-list.txt
groups command displays all the names of groups a user is a part of like this.
groups groups eldernode
Gzip helps to compress a file, replaces it with one having a .gz extension as shown below:
gzip passwds.txt cat file1 file2 | gzip > foo.gz
gunzip expands or restores files compressed with gzip command like this.
head command is used to show first lines (10 lines by default) of the specified file or stdin to the screen:
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head
history command is used to show previously used commands or to get info about command executed by a user.
You can print or set the system hostname in Linux, using the hostname command.
hostname hostname NEW_HOSTNAME
hostnamectl command controls the system hostname under systemd. It is used to print or modify the system hostname and any related settings:
hostnamectl sudo hostnamectl set-hostname NEW_HOSTNAME
hwclock is a tool for managing the system hardware clock; read or set the hardware clock (RTC).
sudo hwclock sudo hwclock --set --date 8/06/2017
hwinfo is used to probe for the hardware present in a Linux system like this.
id command shows user and group information for the current user or specified username as shown below.
ifconfig command is used to configure Linux systems network interfaces. It is used to configure, view, and control network interfaces.
ifconfig sudo ifconfig eth0 up sudo ifconfig eth0 down sudo ifconfig eth0 172.16.25.125
ionice command is used to set or view process I/O scheduling class and priority of the specified process.
If invoked without any options, it will query the current I/O scheduling class and priority for that process:
ionice -c 3 rm /var/logs/syslog
iostat is used to show CPU and input/output statistics for devices and partitions. It produces useful reports for updating system configurations to help balance the input/output load between physical disks.
ip command is used to display or manage routing, devices, policy routing, and tunnels. It also works as a replacement for well known ifconfig command.
This command will assign an IP address to a specific interface (eth1 in this case).
sudo ip addr add 192.168.56.10 dev eth1
iptables is a terminal-based firewall for managing incoming and outgoing traffic via a set of configurable table rules.
The command below is used to check existing rules on a system (using it may require root privileges).
sudo iptables -L -n -v
iw command is used to manage wireless devices and their configuration.
iwlist command displays detailed wireless information from a wireless interface. The command below enables you to get detailed information about the wlp1s0 interface.
iwlist wlp1s0 scanning
kill command is used to kill a process using its PID by sending a signal to it (default signal for kill is TERM).
kill -p 2300 kill -SIGTERM -p 2300
killall command is used to kill a process by its name.
kmod command is used to manage Linux kernel modules. To list all currently loaded modules, type.
last command displays a listing of last logged in users.
ln command is used to create a soft link between files using the -s flag like this.
ln -s /usr/bin/lscpu cpuinfo
locate command is used to find a file by name. The locate utility works better and faster than it’s found a counterpart.
The command below will search for a file by its exact name (not *name*):
locate -b '\domain-list.txt'
login command is used to create a new session with the system. You’ll be asked to provide a username and a password to login as below.
ls command is used to list the contents of a directory. It works more or less like dir command.
The -l the option enables a long listing format like this.
ls -l file1
lshw command is a minimal tool to get detailed information on the hardware configuration of the machine, invoke it with superuser privileges to get comprehensive information.
lscpu command displays the system’s CPU architecture information (such as number of CPUs, threads, cores, sockets, and more).
lsof command displays information related to files opened by processes. Files can be of any type, including regular files, directories, block special files, character special files, executing text reference, libraries, and stream/network files.
To view files opened by a specific user’s processes, type the command below.
lsof -u eldernode
lsusb command shows information about USB buses in the system and the devices connected to them like this.
man command is used to view the on-line reference manual pages for commands/programs like so.
man du man df
md5sum command is used to compute and print the MD5 message digest of a file. If run without arguments, debsums checks every file on your system against the stock md5sum files:
mkdir command is used to create single or more directories if they do not already exist (this can be overridden with the -p option).
mkdir eldernode-files OR mkdir -p eldernode-files
more command enables you to view through relatively lengthy text files one screenful at a time.
mv command is used to rename files or directories. It also moves a file or directory to another location in the directory structure.
mv test.sh sysinfo.sh
nano is a popular small, free and friendly text editor for Linux; a clone of Pico, the default editor included in the non-free Pine package.
To open a file using nano, type:
nc (or netcat) is used for performing any operation relating to TCP, UDP, or UNIX-domain sockets. It can handle both IPv4 and IPv6 for opening TCP connections, sending UDP packets, listening on arbitrary TCP and UDP ports, performing port scanning.
The command below will help us see if port 22 is open on the host 192.168.56.5.
nc -zv 192.168.1.5 22
netstat command displays useful information concerning the Linux networking subsystem (network connections, routing tables, interface statistics, masquerade connections, and multicast memberships).
This command will display all open ports on the local system:
netstat -a | more
nice command is used to show or change the nice value of a running program. It runs specified command with an adjusted niceness. When run without any command specified, it prints the current niceness.
The following command starts the process “tar command” setting the “nice” value to 12.
nice -12 tar -czf backup.tar.bz2 /home/*
nmap is a popular and powerful open-source tool for network scanning and security auditing. It was intended to quickly scan large networks, but it also works fine against single hosts.
The command below will probe open ports on all live hosts on the specified network.
nmap -sV 192.168.56.0/24
nproc command shows the number of processing units present in the current process. Its output may be less than the number of online processors on a system.
The openssl is a command-line tool for using the different cryptography operations of OpenSSL’s crypto library from the shell. The command below will create an archive of all files in the current directory and encrypt the contents of the archive file:
tar -czf - * | openssl enc -e -aes256 -out backup.tar.gz
passwd command is used to create/update passwords for user accounts, it can also change the account or associated password validity period. Note that normal system users may only change the password of their own account, while root may modify the password for an account.
pidof displays the process ID of a running program/command.
pidof init pidof cinnamon
ping command is used to determine connectivity between hosts on a network (or the Internet):
ps shows useful information about active processes running on a system. The example below shows the top running processes by highest memory and CPU usage.
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head
pstree displays running processes as a tree that is rooted at either PID or init if PID is omitted.
pwd command displays the name of current/working directory as below.
rdiff-backup is a powerful local/remote incremental backup script written in Python. It works on any POSIX operating system such as Linux, Mac OS X.
Note that for remote backups, you must install the same version of rdiff-backup on both the local and remote machines. Below is an example of a local backup command:
sudo rdiff-backup /etc /media/eldernode/Backup/server_etc.backup
reboot command may be used to halt, power-off, or reboot a system as follows.
rename command is used to rename many files at once. If you have a collection of files with “.html” extension and you want to rename all of them with the “.php” extension, you can type the command below.
rename 's/\.html$/\.php/' *.html
rm command is used to remove files or directories as shown below.
rm file1 rm -rf my-files
rmdir command helps to delete/remove empty directories as follows.
scp command enables you to securely copy files between hosts on a network, for example.
scp ~/names.txt [email protected]:/root/names.txt
shutdown command schedules a time for the system to be powered down. It may be used to halt, power-off, or reboot the machine like this.
sleep command is used to delay or pause (specifically the execution of a command) for a specified amount of time.
check.sh; sleep 5; sudo apt update
sort command is used to sort lines of text in the specified file(s) or from stdin, as shown below
split as the name suggests, is used to split a large file into small parts.
tar -cvjf backup.tar.bz2 /home/eldernode/Documents/*
ssh (SSH client) is an application for remotely accessing and running commands on a remote machine. It is designed to offer secure encrypted communications between two untrusted hosts over an insecure network such as the Internet.
stat is used to show a file or file system status like this (-f is used to specify a filesystem).
su command is used to switch to another user ID or become root during a login session. Note that when su is invoked without a username, it defaults to becoming root.
su su eldernode
sudo command allows a permitted system user to run a command as root or another user, as defined by the security policy such as sudoers.
In this case, the real (not effective) user ID of the user running sudo is used to determine the user name with which to query the security policy.
sudo apt update sudo useradd eldernode sudo passwd eldernode
sum command is used to show the checksum and block counts for each specified file on the command line.
sum output file.txt
tac command concatenates and displays files in reverse. It simply prints each file to standard output, showing the last line first.
tail command is used to display the last lines (10 lines by default) of each file to standard output.
If there more than one file, precede each with a header giving the file name. Use it as follow (specify more lines to display using -n option).
tail long-file OR tail -n 15 long-file
talk command is used to talk to another system/network user. To talk to a user on the same machine, use their login name, however, to talk to a user on another machine using ‘[email protected]’.
talk person [ttyname] OR talk‘[email protected]’ [ttyname]
tar command is the most powerful utility for archiving files in Linux.
tar -czf home.tar.gz .
tee command is used to read from standard input and prints to standard output and files as shown below.
echo "Testing how tee command works" | tee file1
The tree command is a tiny, cross-platform command-line program used to recursively list or display the content of a directory in a tree-like format.
time command runs programs and summarizes system resource usage.
time wc /etc/hosts
top program displays all processes on a Linux system in regards to memory and CPU usage and provides a dynamic real-time view of a running system.
touch command changes file timestamps, it can also be used to create a file as follows.
tr command is a useful utility used to translate (change) or delete characters from stdin, and write the result to stdout or send to a file as follows.
cat domain-list.txt | tr [:lower:] [:upper:]
uname command displays system information such as operating system, network node hostname kernel name, version, and release, etc.
Use the -a option to show all the system information:
uniq command displays or omits repeated lines from the input (or standard input). To indicate the number of occurrences of a line, use the -c option.
uptime command shows how long the system has been running, the number of logged on users, and the system load averages as follows.
users command shows the user names of users currently logged in to the current host like this.
vim (Vi Improved) popular text editor on Unix-like operating systems. It can be used to edit all kinds of plain text and program files.
w command displays system uptime, load averages, and information about the users currently on the machine, and what they are doing (their processes) like this.
wall command is used to send/display a message to all users on the system as follows.
wall “This is Eldernode – Linux How Tos”
watch command runs a program repeatedly while displaying its output on fullscreen. It can also be used to watch changes to a file/directory. The example below shows how to watch the contents of a directory change.
watch -d ls -l
wc command is used to display newline, word, and byte counts for each file specified, and a total for many files.
wget command is a simple utility used to download files from the Web in a non-interactive (can work in the background) way.
wget -c http://ftp.gnu.org/gnu/wget/wget-1.5.3.tar.gz
whatis command searches and shows a short or one-line manual page description of the provided command name(s) as follows.
which command displays the absolute path (pathnames) of the files (or possibly links) which would be executed in the current environment.
who command shows information about users who are currently logged in like this.
whereis command helps us locate the binary, source, and manual files for commands.
xargs command is a useful utility for reading items from the standard input, delimited by blanks (protected with double or single quotes or a backslash) or newlines, and executes the entered command.
The example below shows xargs being used to copy a file to multiple directories in Linux.
echo /home/aaronkilik/test/ /home/aaronkilik/tmp | xargs -n 1 cp -v /home/aaronkilik/bin/sys_info.sh
yes command is used to display a string repeatedly until when terminated or killed using [Ctrl + C] as follows.
yes "This is Eldernode - Linux HowTos"
youtube-dl is a lightweight command-line program to download videos and also extract MP3 tracks from YouTube.com and a few more sites.
The command below will list available formats for the video in the provided link.
youtube-dl --list-formats https://www.youtube.com/watch?v=iR
zcmp and zdiff minimal utilities used to compare compressed files as shown in the examples below.
zcmp domain-list.txt.zip basic_passwords.txt.zip zdiff domain-list.txt.zip basic_passwords.txt.zip
zip is a simple and easy-to-use utility used to package and compress (archive) files.
tar cf - . | zip | dd of=/dev/nrst0 obs=16k zip inarchive.zip foo.c bar.c --out outarchive.zip tar cf - .| zip backup -
zz command is an alias of the fasd command-line tool that offers quick access to files and directories in Linux. It is used to quickly and interactively cd into a previously accessed directory by selecting the directory number from the first field as follows.
In this article, you have reviewed A to Z of Linux commands. As we mentioned before, there are a countless number of commands in Linux. The list is possibly longer than we can offer. In case you are interested in reading more about Linux commands, have a look at our articles on Linux Server Monitoring Commands AND if you are a get started user, find your suitable article on 10 useful Linux command Line tricks for Newbies.