A.
addgroup command
The addgroup command is used for adding a group to the system. addgroup can be run in any of the three modes: add a user group, add a system group, or add an existing user to an existing group.
adduser command
The adduser command in Linux is used for adding a user or group to the system. The adduser command is used for adding a user. adduser can be run in any of the five modes: add a normal user, add a system user, add a user group, add a system group, add an existing user to an existing group.
alias command
The alias command can be used to replace a command with user-modified instructions while running the command.
apt command
apt (Advanced Package Tool) command manages different packages including install, remove, update, etc.
apt-get command
apt-get command is quite similar to the apt command. But in apt-get common is generally used in the back-end and has backward compatibility. The apt-get (Advanced Packaging Tool) command is used for retrieving package and managing (install, upgrade, update, remove) the package.
arp command
The arp(Address Resolution Protocol) command in Linux is used to manipulate the system’s ARP cache (ARP table) by displaying, adding, or removing IPv4 addresses from the table.
at command
The at command in Linux schedules one-time jobs to execute at the specified time. The atq, atrm, and batch commands are some extended form of the at command that enables it to list, remove and run scheduled jobs.
awk command
In Linux, awk is a pattern-scanning and text-processing tool. This is used for manipulating data in a file. It scans a file line by line and compares it to an input pattern or sequence. And then awk creates a report on the operation.
B.
bash command
bash is a command language interpreter that executes commands read from standard input(user input) or from a file. When you write the command bash in your terminal, it creates a bash process in your shell. bash is a short form of Bourne-Again SHell. It can take single-character options or multi-character options. bash interprets these options when invoked.
bc command
The command bc in Linux is used as a command line calculator. This command is like a normal numerical calculator. This is a hashed command. The most basic operation of this command is the Arithmetic operation.
bzip2 command
The bzip2 command in Linux/Unix-based systems is a file compressor or decompressor. The bzip2 command can take multiple files and combine them as one. This command can be used to save space. Because compressed file takes up less space than decompressed ones.
C.
cal command
cal command stands for the calendar. It shows calendars in many different formats according to the condition.
cat command
Prints the contents of the file specified. Generally, cat (concatenates) reads the contents of the files fed to its arguments and prints them serially on the terminal.
cd command
Change Directory(cd) allows one to change one’s current directory to the desired directory within the terminal.
chage command
The chage command in Linux is for viewing all the information about user password, like when was it last changed. This command can also be used for setting password expiration time, minimum password age, or maximum password age.
chgrp command
The chgrp command in Linux is used to change the group ownership of specified file/s or directory/ies.
chmod command
chmod is the abbreviation for change mode. The chmod command can be used to alter the permission attributes of system contents.
chown command
The chown (change owner) command can be used to alter the owner of system files & directories.
cmp command
The cmp command in Linux is used for comparing files. This command can be used to compare one file with another or one file with multiple files. It compares the files byte-by-byte. The cmp command is an executable command.
comm command
Function of the comm command in Linux is almost similar to the command cmp. But the difference is the comm command doesn’t work with all types of files. This command only works with sorted files. This command takes two sorted files and compares them according to invoked options.
cp command
Cp is the abbreviation for copy. As the name suggests it copies things from one place to another place. cp copies one or multiple files to the specified destination directory. If the directory doesn’t exist it just renames the files. cp can also be used to copy directories and their contents.
cron command
The cron command in Linux is a unique command that schedules operations. The word cron comes from chronology, clearly indicating that cron is related to time. This command can be used to schedule commands daily, weekly, monthly, or with interruption.
crontab command
The crontab command in Linux is used to create a cron Job. The Crontab command opens a tab inside a text editor. There the cronjob is written. This command has some options that help in editing, removing, or creating a crontab.
curl command
The command word curl stands for Client URL. The curl command in Linux is very important for data transfer. It transfers data over various networks. It’s a command line utility that helps data transfer over from or to the server.
cut command
The cut command in Linux is used for editing. This command can operate on the lines of a certain file. This command is used to remove certain portions from the lines of a file. This command can operate differently depending on what options were invoked.
D.
date command
The date command in Linux is a very basic command. This command is used to print the current date on the terminal of the user. Users can also use this command to set the system date or time.
dd command
dd command converts and copies a file to another directory. This command can be used to create a backup inside the hard drive or an external hard drive.
declare command
The declare command in Linux is a shell built-in command. This command has multiple functions. But the main function of this command is to create shell variables and functions.
df command
df (disk free) command shows the size, used, available space, and mounted on the information of the filesystem.
diff command
diff command finds checks 2 files and shows the difference between 2 files. Normally, it does not change the content of files, but it can generate a script.
dig command
The dig command in Linux enables a user to execute various server-related operations. The command word dig stands for the complete word Domain Information Groper. This command is named in this way because it runs an interrogation operation on DNS name servers.
dmesg command
The dmesg command in Linux is used to display, examine and control the Kernel Ring Buffer of the system. It can be used to find faults or solve issues in the system.
du command
du command means disk usage. Using this command the total usage of the disk and the disk usage of the different files are shown in the terminal.
E.
echo command
The echo common is one of the simplest commands, it prints whatever we give to it.
egrep command
The egrep command is a variation of the grep command that interprets searching patterns as regular expressions. It is basically the grep -E command.
enable command
The enable command in Linux/UNIX-based system is the opposite of the disable command. This command restarts every command that was disabled.
env command
The env command in Linux/UNIX-based system is for showing the current environment of the user. This is the default operation of this command. But there are many options that can be invoked. These operations modify the operation of this command. This is an executable command. It is located in the binary directory inside the root directory.
exec command
The exec command is not an executable command. This command is a shell built-in. This command is useful if the user wants to run a program directly from the bash without creating any extra process.
exit command
exit command exits the terminal. It is a shell command, which means it doesn’t have any man page.
export command
The export command in Linux is shell built-in. This variable deals with variables. But the export command doesn’t affect the existing variables. It makes sure that every environment variable or function is recognized by the child processes.
F.
file command
The file command in Linux returns the type of specified file/s. It makes the system run a number of tests to determine the file type.
find command
The find command searches in real-time not like the locate command from an existing file.
finger command
The finger command in Linux deals with login information. This command gives all the information. This command gives information about all the users that are logged in.
firewall-cmd command
The firewall-cmd command in Linux is an Executable command, which is located in the bin directory of the root directory. This command is useful to view the list of enabled services, this can also be useful for listing zones, and creating ports. There are many other uses too.
free command
The free command in Linux is an Executable program. This command shows the empty and free space in the memory. It can show the space in bytes, kilobytes, megabytes, and gigabytes depending on the option.
fsck command
The fsck(File System Consistency Check) command is used to examine issues and sometimes repair file system/s in Linux devices or mount points. If no explicit file system is specified the command starts checking from the /etc/fstab path.
ftp command
The ftp(File Transfer Protocol) command in Linux is used to transfer files between two remote devices (client and server). It offers the users two modes of data transmission: active mode and passive mode.
G.
getent command
The getent command in Linux is a hashed command. A hashed command is something that in UNIX/UNIX like operating system gives the location of the commands found. The word getent is the short form of get entry. This command gets entries from an existing database.
grep command
The grep command can be used to search patterns in specific files or each file. Then prints the entire line containing the match.
groups command
Groups are used to manage multiple users and permissions. Several users can be members of a group and then the group can have permission for some files or folders to manage permissions.
groupadd command
The groupadd command in Linux is an Executable command. The groupadd command is very important when it comes to dealing with file permissions. This command creates a new file or directory group. Usually, the members of the file group have access permission for the file.
groupmod command
The command word groupmod is a short form of group modification. So it is clear that this groupmod command is used to modify or change the attributes of an existing group.
gunzip command
The gunzip command in Linux is used to decompress files compressed by the gzip, zip, compress, compress -H, or pack commands. It can also be used to display compressed file contents.
gzip command
The gzip command is located in the bin directory of the root directory. Which means this is an executable command. This is a file compression or decompression command. This command reduces the size of files. The gzip file doesn’t change the name or timestamp of the source file.
H.
head command
The head command prints the first(by default 10 lines) few lines of a file.
history command
Executing this command one can view the previously used commands in the terminal.
host command
The host is a command line utility that sends requests to the DNS server for converting domain names to IP addresses and vice versa. If the IDN (internationalized domain name) support is enabled with the command, then it can also accept and display non-ASCII domain names.
hostname command
The hostname command in Linux is used to show the hostname. This command can also be used for setting up a new hostname. This is an executable command which is located inside the root directory.
htop command
htop process is quite similar to the top process but in htop, the user can have interactive control over the top running processes in Linux. htop may need to be installed in the terminal first for usage.
I.
id command
This id command in Linux is for printing information for the user id and group id of each user. The id command is also an executable command. This command also gives information about how many groups a user is member of.
install command
The install command when applied with package managers like yum or apt-get, can be used to install packages in Linux. In general, it can be used for copying files, creating directories, changing permissions as well as the owner/group of the copied file.
ip command
The ip (Internet Protocol) command in Linux is used for internet administration. Using this command you can manage and modify your Network Interfaces, IP addresses, Routing tables, and Neighbour entities.
ifconfig command
The ifconfig (Interface Configuration) command is a Unix/Linux command that is mainly used for Network Configuration and management. This command has been depreciated and now the ip command is used for network management.
iptables command
The iptable command is like a firewall for any network. This command can monitor incoming and outgoing data and gives permission to allow or deny that data. This command has a table that has a set of regulations also known as chains that need to be satisfied first for the system to receive that particular data packet.
J.
jed command
Jed is a text editor just like nano and emacs. It is a beginner-friendly text editor that has a drop-down menu. Jed is a Terminal-based text editor that introduces users to other text editors with much more functionality. There are many different shortcuts available for the Jed text editors.
jobs command
The jobs command displays all the currently running jobs in the system. A job consists of single or multiple processes running using the terminal. They don’t have a pid, but a jobspec number that identifies the currently running job.
K.
kill command
Kill is a built-in command that terminates currently running processes. This is a manual command that can forcefully kill a single process or all current processes using the terminal.
killall command
The killall command is used to terminate all processes based on their name. There’s a difference between the kill and the killall command which is, for the kill command, only a single process is terminated based on the pid. But in the case of the killall, all the processes or cycles involved with the name are terminated.
L.
less command
The less command is used to display the contents of a file on the terminal screen in page by page manner.
ln command
The ln command is used to create a hard or soft link to a file or directory in Linux. This command is especially useful for creating a symbolic link and using it as a shortcut. A backup is also possible to create using a hard link and the ln command is extensively used for that purpose as well.
locate command
The locate command performs the search operation from an existing database and prints the results with the exact directory path.
ls command
Lists the contents, both files, and subdirectories of the current directory by default. It is one of the most used commands, as one can view the contents of a directory without exiting the terminal and perform their desired tasks on the specific contents.
lsof command
lsof (List Open File) command shows all the opened files in the Linux.This command particularly shows the processes that open the files. This allows for finding background running processes as well as malicious software that is using other files and using system resources.
M.
make command
The make command in Linux is a GNU utility that determines which part of a large program needs to recompile and issues necessary commands to do so. Users can also apply make to automatically update some files by creating a makefile that defines the necessary commands for updates and relationships among files.
man command
You are whether a beginner or a professional Linux CLI(Command Line Interface) user, the command you will interact with the most is certainly the man command. The man command enables the user to learn more about a specific command i.e. syntax, options, and arguments of that command.
mkdir command
mkdir is the abbreviation for make directory. As the name suggests the mkdir command can be used to create one or more directories.
mke2fs command
The mke2fs command in Linux is used to create only the extended file systems: ext2, ext3, or ext4 in a specified disk space.
mkfs command
The mkfs(Make File System) command in Linux is used to build a specified file system on the mentioned disk space. It can create various file systems including ext2, ext3, ext4, FAT, BFS, MSDOS, CRAMFS, MINIX, NTFS, etc.
more command
The more command in Linux is used for displaying file contents in the terminal while creating an interactive environment. Users can navigate through the contents using shortcut keys like ENTER, B, SPACE BAR, etc.
mount command
The mount command in Linux is used to attach a child file system in the Linux file system. Linux has a tree file structure that starts with the root (/) and the mount command can attach an additional files system anywhere in the file system communicating with the kernel.
mv command
Mv is the abbreviation for move. As the name suggests it moves things from one place to another place. mv moves one or multiple files to the specified destination directory. If the directory doesn’t exist it just renames the files. mv can also be used to move directories and their contents.
N.
nano command
Nano is another text editor. It is a simple and intuitive text editor that has many different shortcuts and is very light. It comes with the basic Ubuntu install.
ncal command
The ncal command in Linux displays the current calendar. It shows the current month with the current date highlighted. The ncal command is quite similar to the cal command. The main difference is, the ncal command shows the calender in a vertical layout and highlights the date but the cal command does not.
neofetch command
The neofetch command in Linux shows information about the operating system, distribution, kernel data, and much more. This command shows a logo of the distribution of the Linux operating system and also shows information related to the system resources and users.
netstat command
The netstat (Network Statistics) command in Linux is used to find information on the network information and statistics. This command has many different uses and various information like the available connections, routing tables, interface statistics, etc are displayed using this command.
nslookup command
The nslookup (Name Server Lookup) command is used to look for information about a Domain Name System (DNS). This command shows information about the web server, address, domain name, etc.
P.
passwd command
The passwd command can be used to change the password of a specific user.
paste command
The paste command in Linux merges lines from each given text file horizontally, separated by TAB, and shows it in the terminal. If no file is given as an argument, it reads the standard input.
patch command
The patch command updates a file according to the differences between two files produced by the diff command. The differences are stored in a .patch file and applied to the original file to create a patched version of the file.
ping command
ping (Packet Internet Groper) command shows the information about the network information about the host and the server. It can check the internet connection and show the latency between the host and server.
ps command
ps (Process Status) command shows the process status and information about that process.
pwd command
Pwd is the abbreviation for Print Working Directory. As the name suggests, it prints the name of the current/working directory all the way beginning from the root(/) directory.
R.
reboot command
The reboot command in Linux is used to reboot the system. It can also be used to enable or disable the reboot keys: CTRL-ALT-DEL.
rm command
Rm is the abbreviation for remove. As the name suggests it removes things and the removal is permanent, so be cautious while using it. rm can also be used to remove directories and their contents permanently.
rmdir command
The rmdir command in Linux is used to remove only empty directories from the filesystem.
rsync command
The rsync (remote sync) command in Linux is used to remotely sync files and directories from a local host to a remote host. In general, this command is used to sync information by copying from the local host, between 2 systems.
S.
scp command
The scp(Secure Copy) command in Linux is used to securely copy files between two hosts in a network. It offers password authentication and security as a login session.
screen command
The screen command in Linux is used to open and manage many Linux Terminal or command lines in a single session. There are many shortcuts available for this command to increase efficiency and productivity while working with several terminals.
sed command
The sed(Stream Editor) command in Linux is used for basic text operations like search, find and replace, insert or delete on an input a stream of files without opening them. This editor is exceptional because it can perform text transformation in the pipeline.
service command
The service command in Linux is used to manage a service This command can start, stop, restart, or shows the status of services in Linux.
sestatus command
The sestatus command in Linux shows the status of SELinux (Security Enhanced Linux). This command shows the current status, mount, current mode, and different policies. This helps in the protection of servers and systems that require security.
sftp command
The sftp(Secure File Transfer Protocol) is an interactive file transfer program, similar to ftp but secure as it uses ssh(Secure Shell) encryption.
shred command
The shred command is used to completely remove data and make it hard to recover later on. This command overwrites data multiple times so it is very difficult for a third party to recover the lost data. It’s equivalent to shredding or destroying documents.
shutdown command
shutdown command is used to shut down the system with some conditions. This command can schedule a shutdown at a specific time or cancel an already scheduled shutdown. The superuser sudo permission is required for this command.
sleep command
The sleep command in Linux is used to pause the terminal for a specified period of time. The default time unit is seconds, but time in minutes (m), hours (h), and days (d) can also be specified.
sort command
sort command sorts the content inside a file and shows it in the display. By default sort command sort alphabetically. But different conditions can be applied for flexibility.
source command
The source command in Linux is used to read the content of the file and then execute the commands inside the file. This command doesn’t create a new shell like the bash command but opens a new variable inside the same shell.
split command
The split command is used to break a large file into smaller files named PREFIXaa, PREFIXab, PREFIXac, and so on. By default the PREFIX is “x” and the default number of lines per split is 1000.
ssh command
ssh (Secured Shell) command is used for securely connecting to a remote server.
stat command
The stat command in Linux is used to print files and filesystem information such as file size, access time, user permissions, etc.
su command
The su (Substitute User) command in Linux is used to substitute the user command and run commands with the privilege of another account. By default, the root user command sudo is needed to run this command.
sudo command
Sudo can be referred to as the supreme command. It is the abbreviation for “Super User DO”. It allows a user to act as a superuser and run commands accordingly. One can run certain commands prefixed by sudo with boosted rights. It is considered analogous to the “run as administrator” process of Windows.
sync command
The sync(Synchronize) command in Linux is used to write all cached file data and unresolved modifications to the underlying filesystem.
T.
tail command
The tail command prints the last(by default 10 lines) few lines of a file.
tar command
The tar (Tape ARchive) in Linux is used to manage archive files in Linux. This command can create, and execute tar files by extracting them. This command can also show information about the files inside the compressed file.
tcpdump command
The tcpdump command in Linux captures, analyzes, and prints the description of packets going through the network.
tee command
The tee command in Linux is used to read the standard input and write it to both standard output and specified file/s.
time command
The time command in Linux runs a specified program command and returns it’s timing statistics like real-time taken, user CPU time, system CPU time, etc. as output.
top command
top (Table Of Processes) command shows the currently running process inside Linux. It gives a dynamic but not interactive view of the process.
touch command
The touch command allows us to update a file’s access or modification time. However, if the file doesn’t exist we can create that file. This ability to create files makes the touch command one of the most useful commands.
tr command
The tr command in Linux is used to perform several character transformations such as uppercase to lowercase, squeezing, deleting, find and replace, translate, etc. to the standard input, and write them to the standard output.
traceroute command
traceroute command displays the packet route to reach the host. This command can be used to see the different hops or routes it takes to connect with a particular hostname.
tree command
The tree command in Linux can list all the files and folders inside a directory in a tree format. This command can show details about the files paths/locations, permissions and owner/group information like the ls command.
tty command
The terminal in Linux OS is represented as a file. The tty command in Linux returns terminal information by displaying the file name of the terminal connected to standard input.
U.
ufw command
The ufw (Uncomplicated FireWall) command in Linux is used as a firewall management command. This command lets the user set firewall information intuitively, whereas the iptable command can achieve the same feat albeit with much more complications
unalias command
The unalias command in Linux is used to remove any aliases created before. This command can remove a specific alias or remove all aliases at the same time.
uname command
uname command shows information about the system. Without any option it prints Linux.
uniq command
The uniq command in Linux is used to identify adjacent duplicate lines in an input file and merge them to write in an output file. It basically omits the adjacent repeated lines in a file.
uptime command
The uptime command in Linux is used to display how long the system has been running along with the current time, the number of logged-in users, and the system load averages for the past 1, 5, and 15 minutes.
unzip Command
unzip command is used to extract files from a .zip file. This command creates a new folder in the current directory where the field inside the zip files is extracted.
useradd command
useradd command is used to add a user to the Linux system. sudo command is needed to create a new user. The superuser sudo command is required to use this command.
usermod command
The usermod command in Linux can modify user-login data. This command can set/change passwords, home directory, expiry date, groups, etc of a user.
users command
The users command in Linux is used to display the list of currently logged-in users to the system.
V.
vi command
Vi is a popular text editor available for almost all Linux distributions. This text editor is very lightweight as a text editing interface, has many shortcuts, and even has different editing modes.
vim command
Vim (Vi Improved) is another text editor derived from the vi text editor. This text editor has many features above vi text editor like multiple widows, command line editing, syntax highlighting based on commands and a complete help system.
vmstat command
The vmstat command is used to display virtual memory information such as processes, memory, paging, block IO, traps, disks, and CPU activity. The first generated report provides details since the last reboot. The following reports are displayed after a sampling period of delay.
W.
wc command
wc (Word count) command is used to count the number of characters or the number of lines in a file.
wget Command
wget is a download command which downloads files or webpages non-interactively from the network.
whatis command
The whatis command in Linux is used to find single-line information from the man page about a command or keyphrase. This command can search through the manual page descriptions and all available matches in a list format.
whereis command
The whereis command in Linux shows the location or path of the binary, manual, and source file of a command. This command points out the location where the information about a command resides.
which command
The which command in Linux searches for the path in the $PATH Environment Variable and shows the complete absolute path. This command locates the executable files in the path and shows the results in the command line.
who command
The who command in Linux is used to list the currently logged-in users in the system and their information. This information includes login name, login time, hostname, current system run level, etc.
whoami command
The whoami command simply displays the currently logged-in user.
X.
xargs command
The xargs command in Linux is used to read standard input and then convert it to an argument for another command. This command builds and executes other commands from standard input.
Z.
zip Command
zip command is used to compress files or folders into a .zip file in UNIX and UNIX-like operating systems. This allows for reducing the size of files and disk usage. Converting many files, and folders into a .zip file allows sharing and maintaining disk location by reducing file zie without any loss.
