FUNDAMENTALS A Complete Guide for Beginners
With this article ‘Top 100 Linux Commands’, get to explore the world of Linux Commands, that every Linux user should know. From file management and networking to system administration, these commands cover a wide range of functionalities. Whether you are a beginner or an experienced user, this curated collection will give you the necessary skills to navigate the entire area of Linux Command-Line tools.
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List of Top 100 LINUX Commands
Following, I will give a list of 100 top Linux commands with their description, syntax & useful options. You can also learn more about these commands with necessary examples & practical usages by visiting the corresponding attached link that is appended after each command.
1. ls
The 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.
Syntax
ls [OPTION]... [FILE]...Useful Options
- -a → Doesn’t ignore the hidden files (files named with .(dot) at the beginning).
- -h → Prints sizes in human-readable forms.
- -l → Lists in a long form.
- -S → Sorts according to file size, largest first.
- -d → Only lists the current directory, not its contents.
2. cd
The word cd stands for change directory. This command is used for changing the current directory of the user. It will take the user from the current directory (current location) to a specified directory.
Syntax
cd [OPTION]... [DIRECTORY]Useful Options
- cd ~[username] → Changes the directory to the home directory of the specified user.
- cd .. → Changes directory one directory up the current directory.
- cd – → Changes the directory to the previously changed directory.
3. pwd
The pwd command stands for print working directory. It displays the Absolute path of the current directory, in a simple context, prints the name of the current/working directory all the way beginning from the root(/) directory. So it shows where the Terminal currently is in detail and will help you when you are lost inside some unknown directory.
Syntax
pwd [OPTION]...Useful Options
- -L, –logical → Even as it carries symlinks, PWD utilizes from the environment.
- -P, –physical → Avoids the symlinks.
When no option is mentioned, it is assumed that option -P is being used.
4. mkdir
The command mkdir is the abbreviation for make directory. As the name suggests, the mkdir command is used to create one or more directories.
Syntax
mkdir [OPTION]... DIRECTORY...Useful Options
- -p – -parents → Creates the necessary parent directories if required.
- -v, –verbose → Prints message of what is being performed.
5. rm
The rm command is the abbreviation for remove. As the name suggests, it removes files and the removal is permanent, so be cautious while using it. The command can also be used to remove directories and their contents permanently.
Syntax
rm [OPTION]... [FILE]...Useful Options
- -i → Displays interactive prompt before completing the deletion each time.
- -I → Only shows prompt while deleting 3 or more files or deleting recursively.
- -d, –dir → Removes the empty directories.
- -R, -r, –recursive → Removes any directory as well as its contents recursively.
- -v, –verbose → Prints message of what is being performed.
6. rmdir
The rmdir command in Linux is used to remove only “empty directories.” In addition, if you try to remove a non-empty directory using the rmdir command, it will prompt the “Directory not empty” error message by preventing accidentally removing the non-empty directories. And this decreases the risk of losing necessary data.
Syntax
rmdir [OPTION]... DTRECTORY_NAME...Useful Options
- –ignore-fail-on-non-empty → Ignore each failure that is only because a directory is non-empty.
- -p, –parents → Remove the directory along with its empty content Directories.
- -v, –verbose → Generate a diagnostic report for each file that is processed.
7. touch
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.
Syntax
touch [OPTION]... FILE...Useful Options
- -a → changes only the access time.
- -m → Changes only the modification time.
8. cp
The cp command resembles the word ‘copy’. As the name suggests, it copies things from one place to another place. The command can copy one or multiple files to the specified destination directory. If the directory doesn’t exist it just renames the files. It can also be used to copy directories and their contents.
Syntax
The Syntax For Copying Files
cp [OPTION]... [-T] SOURCE DESTINATIONFor Copying Files to a Directory
cp [OPTION]... SOURCE… DIRECTORYCopying Directory
cp [OPTION]... SOURCE DIRECTORY DESTINATION DIRECTORYUseful Options
- -i, –interactive → Displays interactive prompt before completing the modification.
- -R, -r, –recursive → Copies the directory as well as its contents recursively.
- -v, –verbose → Prints message of what is being performed.
9. mv
The mv command is a widely used file/folder management command that allows changing the location of a file or folder. Moreover, when changing the location you can rename the file as well just by changing the file name.
Syntax
mv [OPTION]... SOURCE... DESTINATIONUseful Options
- -n, –no-cobber → Does not overwrite an existing file.
- -i, –interactive → Prompts before overwriting.
- -f, –force → Does not prompt before overwriting.
- -v, –verbose → Explains what is being done.
- -u, –update → Moves only when the source file is newer than the Destination file.
10. dd
The 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.
Syntax
dd [OPERAND]...dd OPTIONUseful Operands
- bs=BYTES → Reads/Writes up to a given number of BYTES at a time i.e. block size.
- cbs=BYTES → Converts a given number of BYTES at a time.
- conv=CONVS → Converts file as per the following symbols-
ascii: from EBCDIC to ASCII.
ebcdic: from ASCII to EBCDIC.
lcase: changes upper case to lower case.
ucase: changes lower case to upper case.
- sync → Synchronizes I/O for both data and metadata.
- count → Indicates the number of blocks
- ibs=BYTES → Reads up to a given number of BYTES at a time.
- of=FILE → Writes to FILE.
- if =FILE → Reads from FILE.
- seek=N → Skips N obs-sized blocks at the start of the output.
- skip=N → Skips N obs-sized blocks at the start of input.
The mentioned N and BYTES can have values from the following multiplicative suffixes:
- c=1,
- w=2,
- b=512,
- kB=1000,
- K=1024,
- MB=1000*1000,
- M=1024*1024,
- xM=M,
- GB=1000*1000*1000,
- G=1024*1024*1024, and so on for T, P, E, Z, Y.
- Binary prefixes can be used, too:
- KiB=K,
- MiB=M, and so on.
Useful Options
- if → Read the file instead of standard input.
- of → Write the file instead of the standard output.
11. cat
The 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.
Syntax
cat [OPTION]... [FILE]...Useful Options
- -E, –show-ends → Display $ at end of each line.
- -n, –number → Displays line numbers when utilized.
- -s, –squeeze-blank → suppress repeated empty output lines.
12. less
The less command is a handy command in Linux that shows any file’s contents one page at a time. This command is more useful when viewing a large file with many lines because it doesn’t load the entire file, so it gives a fast loading speed. You can navigate through the lines of text using the ARROW keys and navigate page to page using the SPACE bar.
Syntax
less [OPTIONS]... (FILE_PATH or FILE_NAME)Useful Options
- -n –line-numbers → When enabled it stops showing line numbers.
- -N –LINE-NUMBERS → Displays line numbers at the starting points of each line.
13. head
The head command prints the first (by default 10 lines) few lines of a file. You can also print the first specific lines or bytes from a file using the head command in Linux.
Syntax
head [OPTION]... [FILE]...Useful Options
- -n → Prints the first n lines.
- -v, –verbose → Prints message of what is being performed.
14. tail
The tail command outputs the last (by default 10 lines) few lines of a file. But it can also be used to view only data instead of lines easily. Moreover, this command can be used to show specific file lines too.
Syntax
tail [OPTION]... [FILE]...Useful Options
- -n NUM → Shows NUM number of lines in the command line output.
- -n +NUM → Shows all the lines after NUM number of lines.
- -f, –follow → Follows any addition to the file and updates the output in the command line.
- -q, –quiet, –silent → Doesn’t output the header line with the output.
- -v, –verbose → Outputs header file names.
- -s, –sleep-interval → Sets the timer interval of update for the -f
15. grep
The grep command is very useful for searching files and directories containing matching words or character lines. Then it prints the entire line containing the match. It is the shortcut for “Global Regular Expression Print”.
Syntax
grep [OPTION]... PATTERNS [FILE…]Useful Options
- -c, –count → Does not print any matches but rather the total occurring number.
- -i, –ignore-case → Ignores the sensitivity of cases.
- -v, –invert-match → Invert the sense of matching, to select non-matching lines.
- -w, –word-regexp → search for a whole word.
16. locate
The locate command performs the search operation from an existing database and prints the results with the exact directory path.
Syntax
ls [OPTION]... PATTERN...Useful Options
- -c, –count → Does not print any matches but rather the total occurring number.
- -e, –existing → Only prints the existing match.
- -i, –ignore-case → Ignores the sensitivity of cases.
- -p, –nofollow → Ignores punctuation and spaces when matching patterns.
- -l, N, –limit=N → Stop searching after limit matches have been found.
17. find
The find command in Linux performs the task of searching & listing files and directories in a directory hierarchy in real time, not like the locate command from an existing file.
Syntax
find [OPTIONS] [PATH] [EXPRESSION]Useful Options
- -type d/f → Where, d (limits the search to only directories), f (limits the search to only files).
- -size +n,n,-n → Finds for a specific size n.
- -name pattern → Searches for the given pattern.
- -exec → Performs our customized tasks on the matches.
18. chmod
The chmod command is the abbreviation for change mode. The chmod command can be used to alter the permission attributes of system contents.
Syntax
- Syntax 1
chmod [OPTION]... MODE[,MODE]... FILE…- Syntax 2
chmod [OPTION]... OCTAL-MODE FILE…- Syntax 3
chmod [OPTION]... - -reference=RFILE FILE…Here, MODE can be specified alphabetically or in OCTAL number format.
Useful Options
- -R, –recursive → Changes files and directories recursively.
- -v, –verbose → Outputs a Diagnostic when a file is processed.
- -c, –change → Reports only when a change is made.
- -f, –silent, –quiet → Suppresses most error massages.
- –version → Outputs version information and exit.
- –help → Displays this help and exit.
19. chown
The word chown stands for Change Owner. As the name says, this command is used for changing owners. When I say Change Owner I mean changing both file owner and group owner. The chown command is very useful when it comes to accessing the permission of a file or directory.
Syntax
chown [OPTION]... [OWNER] [:[GROUP]] FILE…chown [OPTION]... --reference=RFILE FILE…Useful Options
- -R, –recursive → Changes files and directories recursively.
- -v, –verbose → Outputs a Diagnostic when a file is processed.
- -c, –change → Reports only when a change is made.
- -f, –silent, –quiet → Suppresses most error massages.
- –version → Outputs version information and exit.
- –help → Displays this help and exit.
20. chgrp
The chgrp command, short for “change group“, is a useful tool in Linux for managing file permissions and access control. It alters the group name that a file or directory belongs to, which in turn affects the permissions that users have to access and modify the file.
Syntax
chgrp [OPTION]... [GROUP_NAME] [DIRECTORY/FILE_NAME]...Useful Options
- -c, –changes → Works like verbose but reports only when a change is made.
- -f, –silent, –quiet → Can be used to suppress error messages.
- -v, –verbose → Generates a diagnostic report for each file that is processed.
- –dereference → Modifies the referent of each symbolic link (the default behavior) instead of the symbolic link itself.
- –no-preserve-root → Does not treat root directory ‘/’ specially (the default).
- –preserve-root → Fails to operate recursively on root directory ‘/’.
- –reference=RFILE → Employs the group of RFILE instead of specifying a GROUP value.
- -R, –recursive → Performs actions on files and directories recursively.
21. tar
The tar command in Linux is used to archive files into a tar archive. Using the command options, you can also compress file size with bzip2 & gzip. While creating a tar archive using the tar command, it always keeps the original files. This command is also used to extract files from the tar archive in different ways.
Syntax
tar [OPTION]... [FILE]Useful Options
- -c → Creates uncompressed tar archive.
- -x → Extracts files from the tar archive.
- -v → Displays archived files of the tar archive.
- -f → Sets the name of a tar archive.
- -t → Displays the list of the tar archive.
- -j → Creates tar archive with bzip2.
- -z → Creates tar archive with gzip.
- -r → Updates files/directories of the existing tar archive.
- –wildcards → Specifies patterns of archived files of a tar archive.
- –delete → Deletes file/directory from the tar archive.
22. gzip
gzip command in Linux is used to compress & decompress files. The file size is decreased without losing data using this command in Linux. This command can also be used to test the integrity of the compressed files. Like some other compression commands, it replaces the original file while compression.
Syntax
gzip [OPTION]... [FILE]...Useful Options
- -f → Forces compression of the file & removes the original file.
- -k → Compresses file but does not remove the original file.
- -r → Compresses all files of a specified directory.
- -v → Displays the name & percentage of reduction of file.
- -d → Decompresses file that is compressed.
23. gunzip
The gunzip command in Linux is used to decompress the compressed files. It is used to check the integrity of the compressed files as well as the percentage reduction of the files in Linux. This command can also be used to display the contents of the compressed files. Like some other decompression commands, it replaces the original file while decompression.
Syntax
gunzip [OPTION]... [FILE]...Useful Options
- -k → Compresses file but does not remove the original file.
- -v → Displays the name & percentage of reduction of file.
- -l → Displays information about the compressed files.
- -c → Displays contents of the compressed files.
24. zip
The zip command is a simple command that helps compress the file size to save disk space. Compressed files are easier to transfer and less time-consuming.
Syntax
zip [OPTIONS] File.zip File…Useful Options
- -r → Zips a directory.
- -d → Removes specified files without unzipping.
- -m → Deletes the original file after zipping.
- -x → Excludes specified files from zipping.
- -e → Creates a password-protected zip archive.
- -s → Splits a large zip file into parts.
25. unzip
The unzip command extracts all the files & directories from the zip file in the current directory. This command also displays the list of files & directories it is extracting from the zip file in the terminal.
Syntax
unzip [OPTION]... [FILE]Useful Options
- -d → Extracts files to the specified directory.
- -l → Lists contents of zip(compressed) file.
- -t → Checks if the zip file is a valid zip archive or not.
- -v → Displays detailed info of each file inside a zip archive.
- -x → Extracts only mentioned files.
26. ssh
The “ssh” of the ssh command in Linux stands for “Secure Shell”.This command in Linux is used to securely connect two computers (client and server) following the SSH protocol. You can execute commands from a remote location and transfer data using the ssh command. The data transfer is encrypted which prevents hackers from accessing them.
Syntax
ssh [OPTION]... username@ip_addressUseful Options
- -4 → Only uses IPv4 addresses.
- -6 → Only uses IPv6 addresses.
- -C → Compresses data.
- -i → Used to log in with a private key.
- -l → Specifies the user.
- -p → Used to specify a port.
27. scp
The “scp” of the scp command in Linux stands for “Secure Copy”. It is used to copy files between two computers (client and server). It uses the SSH (Secure Shell) protocol which provides secure communication over an insecure network.
Syntax
The scp command in Linux has two syntaxes, one for upload and the other for download. For uploading:
scp [OPTION]... SOURCE username@IP_address:DESTINATIONFor downloading:
scp [OPTION]... username@IP_address:SOURCE DESTINATIONHere,
- SOURCE means the path to the file which will be copied.
- DESTINATION means the path where will the file be copied.
- username denotes the username of the server.
- IP_address denotes the IP address of the server.
Useful Options
- -4 → Only uses IPv4.
- -6 → Only uses IPv6.
- -C → Compresses
- -P → Used for logging in with a specific port.
- -v → Enables verbose
- -r → Copies recursively.
28. sync
The sync command allows putting your data in sync both in permanent storage & volatile memory. It makes sure all buffered modifications made to file metadata and data are written to the underlying file systems. Every Linux user should use the sync command before unusually halting the processor to save all the cache data.
Syntax
sync [option]... [file]...Useful Options
- -d, –data → Syncs only the data of the filesystem, and essential metadata.
- -f, –file-system → Syncs the filesystem containing the specified files.
29. rsync
The rsync command in Linux is used to synchronize files and directories between two computers (local host and remote host). At first, it uses SSH(Secure Shell) to connect to a remote host and decides which part of local files (or directories) is needed to be copied. The rsync command is an efficient way to transfer files as the manual method is tedious.
Syntax
rsync [OPTION]... SOURCE DESTINATIONUseful Options
- -a → Copies attributes of data.
- -h → Shows data in a human-readable
- -v → Enables verbose mode.
- -z → Compresses
- –progress → Shows progress report.
- –ignore-existing → Ignores already existing files in the server.
- –delete → Removes files from the server when they are deleted in the client.
- –remove-source-files → Automatically deletes files after syncing.
- –chmod → Sends file permissions.
- –dry-run → Performs a dry run.
- –max-size → Sets maximum file size.
- –bwlimit → Sets maximum bandwidth.
30. man
The man command in Linux stands for manual. Upon execution, it will display a manual page or documentation of a specified Linux command. It displays information like the synopsis, description, options, exit status, authors, copyright, etc.
Syntax
man [OPTION]... [Command_NAME]... Useful Options
- SECTION COMMAND → Shows the specific SECTION of a COMMAND.
- -k KEYWORD → Search for the Keyword in the whole manual page and show all the matches.
- -f KEYWORD → Looks for a short description of any Keyword or Command.
- -d, –default → Resets the man command behavior to default.
- -i, –ignore-case → Ignore case sensitivity of the command.
- -I, –match-case → Looking inside the man page with case sensitivity.
- -a, –all → Shows all manual pages that match the specific keyword or command.
31. alias
The alias command in Linux is used as a shortcut that takes a string that can execute a command and replaces it with another string of text. This command can replace a large complex command with a relatively simple string and reuse that command many times. Professionals use this command quite a lot to increase their functionality.
Syntax
alias [option] [name]=’[value]’Useful Options
- -p → Lists all available aliases in the command line.
- –help → Shows the help page of the alias command.
32. unalias
The unalias command is used to eliminate items from the list of aliases for the current user, specifically those added during the current login session. Permanent aliases may also be temporarily suppressed; however, they will be restored once the user logs in again.
Syntax
unalias [OPTION] [ALIAS_NAME]...Useful Options
- -a → Removes all alias for the current user for the current shell for the current session.
33. history
The history command displays the previously executed commands and a number to imply a serial is also shown with this command. This command will help you recall any command you’ve used before but forgot about it.
Syntax
The history command has a really simple syntax. Just type history and that’s it. You can also add a number after the command to show how many previously executed commands you want to see in the command line.
But on the man page, there is no syntax available for the history command.
Useful Options
- -d EVENT_NUM → Deletes the instance with the event number of EVENT_NUM.
- -c → Deletes all the history.
34. sudo
The sudo command allows a permitted user to execute a command as the superuser or another user, as specified by the security policy. It is considered analogous to the “run as administrator” process of Windows.
Syntax
sudo [OPTION]...[COMMAND]...Useful Options
- -D directory, –chdir=directory → Executes the command in the specific directory.
- -e → Edits one or multiple files instead of executing commands.
- -h → Displays a short help message and exits.
- -l → Runs specific commands as the root user.
- -k → Kills the user’s timestamps.
- -u user, –user=user → Executes the command as a user other than the specific default user.
35. su
The su command is an excellent tool to secure multiple-user systems, enabling you to switch from one user to another.
Syntax
su [options] [-] [user [argument...]]Useful Options
- -c, –command=command → Passes the command to the shell with the -c
- -f, –fast → Passes -f to the shell, which may or may not be helpful, depending on the shell.
- -g,–group=group → Specifies the primary group. This option is available to the root user only.
- -G, –supp-group=group: Specifes a supplementary group. This option is available to the root user only. The first specified supplementary group is also used as a primary group if the –group option is not specified.
- –h, –help → Shows the help file for the su command.
- -, -l, –login → Starts as a login shell with an environment similar to a real login.
- –p, –preserve–environment → Preserves the shell environment.
- –s, –shell → Allows you to specify a different shell environment to run in.
36. ip
The ip command in Linux allows users to display as well as manipulate routing tables, network interfaces, and devices. You can extract various network information using this command. In addition to other applications, you can also assign new IP addresses using this command.
Syntax
ip [OPTION]... OBJECT COMMANDadd
delete/del
show
Useful Options
- -br, –brief → Displays only basic information.
- -h, –human → Displays human-readable values.
- -4 → Filters only the IPv4 addresses.
- -6 → Filters only the IPv6 addresses.
37. iptables
The iptables command in Linux is used to set up, maintain, and inspect the tables of IP packet filters. These tables contain built-in chains which are basically a set of rules to match packets going through the network. Each rule defines the action performed on a set of packets.
The Linux-based Firewall is maintained by the IPv4/IPv6 packet filtering command iptables. The Firewall rules within this table specify targets for each packet. Targets can be any of the following:
- ACCEPT: Lets a packet come through the network.
- DROP: Rejects the packet from entering the network.
- QUEUE: Receives the packet and passes it to the queue.
- RETURN: Stops the current chain and resumes the next rule of the previous chain.
Syntax
iptables [-t table] [OPTION]...Tables
The present Linux distribution comes with five independent tables. A description of each table is given below:
- filter: It is the default table displayed when the -t option is not passed. This table has the following built-in chains: INPUT, OUTPUT, and FORWARD.
- nat: This table is used when packets with a new connection arrive. Includes INPUT, OUTPUT, PREROUTING, and POSTROUTING built-in chains.
- mangle: It is consulted for specialized packet alteration. The two built-in chains within this table are OUTPUT and PREROUTING.
- raw: Configures exemptions from connection tracking. Built-in chains include OUTPUT and PREROUTING.
- security: Used for Mandatory Access Control (MAC) networking rules implemented by Linux Security Modules. It contains INPUT, OUTPUT, and FORWARD built-in chains.
Useful Options
The iptables command options are divided into three main groups:
COMMANDS
These options indicate a certain action to be performed. Only one of the following commands can be applied at a time.
- -A, –append → Appends rule/s to the end of a chain.
- -C, –check → Checks if a specified rule exists.
PARAMETERS
The parameters are used to specify a rule.
- -d, –destination → Specifies destination.
- -p, –protocol → Specifies the protocol of a rule or, packet.
OTHER OPTIONS
These are the available options for the iptables command in Linux.
- –line-numbers → Adds a line number to the beginning of each rule.
- -n, –numeric → Displays numeric IP addresses and port numbers.
38. ping
The ping command shows the connection latency between the host and servers. The ping command takes a URL, and IP address as arguments and shows the latency between the local machine and the server.
Syntax
ping [OPTION]... <Destination>Useful Options
- -c COUNT → Limits Ping requests for packets after COUNT
- -T → Timestamp
- -w → Limits the total time.
- -D → Prints timestamps before each line.
- -f → Floods the network with packets.
- -i → Fixes the interval between each packet sent.
- -q, Quite an output → Nothing is shown in the command line.
- -s → Fixes the packet size
- -v → Provides verbose
- -4 → Uses IPv4
- -6 → Uses IPv6
39. traceroute
The traceroute in Linux is used to track the path a data packet takes. A data packet passes multiple hops to reach its destination. If there are any issues in any network, the traceroute command can be used to find the problem and solve it. That’s why the traceroute command in Linux is a useful network troubleshooting tool.
Syntax
traceroute [OPTION]... [HOST]Useful Options
- -n → Hides
- -f, –first_ttl → Specifies initial hop
- -m, –max_ttl → Sets maximum hops
- -q, –nprobes → Limit the number of tests.
- -w, –waittime → Limits response time.
- -4 → Uses only
- -6 → Uses only
- -F → Enables “Don’t Fragment” mode.
- -g, –gateway → Routes through a certain IP address.
- -d → Disables resolution of the IP address.
- -t, –tos → Specifies the maximum number of hops for a
- -p, –port → Tests a port.
40. wget
The wget which stands for “web get”, allows users to download files from networks using protocols like HTTP, HTTPS, FTP, and FTPS. The non-interactive downloading occurs in the background while a user is disconnected or busy with another process. It utilizes recursiveness by continuously attempting until a file is entirely retrieved. The wget Command in Linux also downloads complete HTML/ XHTML pages and replicates the content structure to browse the websites locally.
Syntax
wget [Option] … [URL] …Useful Options
- – b → Downloads file in the background.
- – c → Continues interrupted downloads,
- – i → Downloads multiple files.
- – t, –tries = [number] → Fixes the number of retry attempts for interrupted downloads.
- – m, — mirror → Mirrors a website locally for offline browsing.
- – r → Turns on Recursive retrieval of files, the default value = 5.
- – A, — accept “*.<FileType>” → Downloads only specific file type.
- – R, — reject “*.<FileType>” → Rejects downloads for specific file type.
- – O, Upper case → Downloads file with a different name.
- – p → Downloads in a specific directory.
- – – limit-rate = [amount] → Limits bandwidth/speed while downloading.
- – – no-check-certificate → Ignores SSL certification check.
41. curl
The curl command in Linux stands for “Client URL”. It is a file transfer command-line tool powered by libcurl, a free client-side URL transfer library. This means it allows you to send or receive data over the network. It supports most of the network protocols ( HTTP, FTP, SFTP, SMTP, TFTP, POP3, TELNET, FILE, etc.). You can use the curl command in Linux to transfer single or multiple files at once.
Syntax
curl [options / URLs]Useful Options
- -C → Continues interrupted downloads.
- -I → Outputs the HTTP header only.
- –limit-rate <amount> → Limits bandwidth/speed while downloading.
- -libcurl <filename> → Output C source code of the URL.
- -L → Redirects if the requested page is moved.
- -o → Downloads file with default different name.
- -O, Upper case → Downloads file with a different name.
42. df
The “df” comes from “disk free”, which displays the size, used & available space, and mounted on the filesystem’s information. As you know, no machine has unlimited disk space, and checking available space is necessary sometimes.
Syntax
df [OPTION]... [FILE]...Useful Options
- -a, –all → Displays all file systems including pseudo, duplicate, and inaccessible.
- -h, –human-readable → Shows sizes in powers of 1024.
- -H, –si → Shows sizes in powers of 1000.
- –output → Prints output in a customized See the manual page for details.
- –total → Ignores insignificant entries to available space and shows a total.
- -t, –type → Only prints a specific type of file system. See the manual page for details.
- -x, –exclude-type → Prints file system excluding specific file system type. See the manual page for details.
- -T, –print-type → Prints file system type.
- -i, –inodes → Llists inodes
43. du
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.
Syntax
du [OPTION]... [FILE]...Useful Options
- -a → Shows the total disk usage.
- -ah → Shows all files disk usage.
- –time → Shows the last modification time.
- -B, –block-size → Defines a new scale.
- -c, –total → Shows total at the end.
- -S, –separate-dirs → Doesn’t show subdirectories.
- –si → Uses 1000 as the scale.
- -s, –summarize → Shows only total disk usage.
44. ps
The ps (Process Status) command shows the process status and information about that process.
Syntax
ps [OPTIONS]Useful Options
- -a, –all → Shows all the processes including hidden processes.
- -r → Shows all the running processes.
- –pid PID → Shows the specific process according to PID.
45. kill
The kill command in Linux is one of the handiest tools that can be used to terminate one or multiple processes from the Terminal. It sends a signal to the process, which ultimately closes, terminates, or kills a particular process or group of processes. If the user doesn’t specify any signal to be sent along with the kill command, then the default TERM signal is sent that terminates the process. It is a very useful tool for multitaskers who handle multiple programs simultaneously.
Syntax
kill command is a built-in command that takes options and PID (process ID) or process name. The syntax of the kill command is as follows.
kill [options] [PID]...Useful Options
- -l → Shows the available option of the kill
- — SIGHUP -1 → Reloads the process.
- — SIGKILL, -KILL, -9 → Terminates the process.
- — SIGTERM, -TERM -15 → Terminates the process.
46. shutdown
The shutdown command in Linux is useful for safely shutting down the system. The machine can be shut off immediately or on a schedule with a 24-hour format. And When executing the command, all currently active users and processes are informed that the system is shutting down. New login attempts are not permitted when it is initiated.
Syntax
shutdown [OPTIONS]... [TIME] [MESSAGE]Useful Options
- -r → Asks for the system to be restarted following a shutdown.
- -h → Equivalent to halt unless power is off depending on the specified option.
- -H → Stops the operating system.
- -P → Powers off the machine.
- -c → Cancels a shutdown that is currently in effect. This can be used to invoke a shutdown with a time argument other than “+0” or “now.”
- -k → Does not halt, power off or reboot, only sends out the warning messages.
47. reboot
Using the reboot command in Linux, any user can restart the whole system using the command line interface.
Syntax
reboot [OPTION]...Useful Options
- -d, –no-wtmp → Does not write wtmp record during reboot.
- –help → Prints a short help text and then exits.
- -f, –force → Forcefully reboots the system.
- –no-wall → Does not send any wall message during reboot.
- -p, –poweroff → Power off the machine.
48. mount
The mount command in Linux is used to attach a removable storage device or filesystem to an existing directory making them accessible. All files on the device are placed in a big tree-like hierarchy, starting from the root directory (noted as / ). Just like the root holds the tree, all the child filesystems emerge like the branches from the root directory. And the mount command helps to mount the device filesystem to the Linux filesystem (large tree structure).
Syntax
mount [OPTION]... <device> <target>Useful Options
- -a –all → Mounts all files listed in /etc/fstab.
- -o –options → Limits the file system set that -a applies to.
- -t –type → Indicates the file system type.
- -T → Specifies an alternative /etc/fstab file.
- -l → Lists all the files mounted and added labels to each device.
- -L –label → Mounts the partition with the specified label.
- -M → Moves the mounted file to another location.
- -r → Mounts the filesystem in read-only mode.
- -R → Remounts a filesystem to a different location, making its contents available in both places.
- -v → Mounts verbosely, describing each operation.
49. date
The date command is one of the most frequently used commands in Linux. It is used to get or set the date and time of the system. This command can also be used to find out the modification time of files and can calculate the past and future dates as well. By default, the date command displays the Central Standard Time (CST) Time Zone. But you can adjust the date view on your terminal as well.
Syntax
date [OPTION]... [+FORMAT]Useful Options
- -d, –date=STRING → Converts time from the string such as today, tomorrow, 1 year ago, etc.
- -f, –file=DATEFILE → Runs date command for each line of the file.
- -s, –set=STRING → Sets time described by the string.
- -r → Returns the last modification time of a file.
- TZ → Prints out time in a given time zone.
- -u → Returns the time in the UTC zone.
50. ncal
The ncal command in Linux is a Unix-based tool to view calendars. However, it doesn’t come by default in most systems and may require to install manually. It is the successor of cal command. It provides advanced formatting compared to the cal command. In addition to that, it has some extra features like showing holidays, the lunar calendar, etc.
Syntax
cal [OPTION]... [ARGUMENT]...Useful Options
- -h → Removes the highlight on the current date.
- -y → Used to view the calendar of a specific year.
- -m, → Shows the calendar of a specific month of the current year.
- -3, → Prints the calendar of previous, current, and following
- -w, → Shows the week number.
- -B, → Displays a specific number of months before the current month.
- -A, → Prints a specific number of months after the current month.
51. whoami
The whoami command simply displays the currently logged-in user. It can be handy while working on a machine with multiple users. It displays the username of the effective user in the current shell. Moreover, It is useful in bash scripting to show who is running the script.
Syntax
whoami [OPTION]...Useful Options
- –help → Displays the man page and exit.
- –version → Output version information and exit.
52. id
The id command in Linux displays current user and group information according to the application of the command. You can modify the usage by passing a specific username or options.
Syntax
id [OPTION]… [USER]Useful Options
- -g, –group → Displays only the effective group ID.
- -G, –groups → Displays all the group IDs of the user.
- -r, –real → Displays real IDs.
- -n, –name → Displays names.
- -u, –user → Display only the effective user ID.
- -z, –zero → Delimits entries with a NULL character.
- -Z, –context → Displays security context of the process.
53. uname
The uname command, short for UNIX name, is a useful tool in Linux for getting information about the hardware and software of the current system including the operating system, kernel, processor architecture, and network node hostname.
Syntax
uname [OPTION]...Useful Options
- -a, –all → Prints all available information about the system, including the kernel name, network node hostname, kernel release, kernel version, machine hardware name, and processor type (excluding the -p and -i options if they are unknown).
- -s, –kernel-name → Displays the kernel name.
- -n, –nodename → Displays the network node hostname.
- -r, –kernel-release → Displays the kernel release.
- -v, –kernel-version → Displays the version of the kernel.
- -m, –machine → Displays the machine hardware name.
- -p, –processor → Displays the type of processor.
- -i, –hardware-platform → Displays the hardware platform (non-portable).
- -o, –operating-system → Displays the operating system name.
54. Bash
The bash command in Linux is a popular tool for starting a shell from the beginning, creating a new login shell, running a bash script from the terminal, etc.
Syntax
bash [OPTIONS] [COMMAND_STRING / FILE]Useful Options
- -c → Creates a new shell different from the current shell and performs the later task on the new shell.
- -i → Makes the shell interactive.
- -l → Makes bash act as if it had been invoked as a login shell.
- -r → Makes the shell restricted)
- -v → Makes shell print input lines as they are read.
- -x → Prints commands and their arguments as they are executed.
55. exit
The exit command is used to end or close the current login session in the Linux ecosystem. Shell or bash jobs as well as the Linux CLI can be closed using this simple command.
Syntax
exit [INTEGER_VALUE] USER_NAMEUseful Options
There are no OPTIONS available for the exit command in Linux.
56. clear
The clear command in Linux clears your terminal screen if possible. It also scrolls down the terminal screen to clear it. It observes the terminal type in the environment given by the environment variable TERM, and then in the terminfo database to decide how the screen can be cleared. Standard output is also written by the clear command in Linux.
Syntax
clear [-OPTION]Useful Options
- -T → Indicates the type of terminal.
- -V → Reports the version of ncurses.
- -x → Scrolls down the terminal, does not remove history.
57. echo
The echo command in Linux takes a string of text and displays the output in the command line. Even though the command may look like a straightforward command, you can also pipe or redirect the echo command with another command to do certain things like create/edit files if you want.
Syntax
Just add your text after the echo command and the command will print everything after the command in the command line.
echo [SHORT-OPTION]... [STRING]...echo LONG-OPTIONUseful Options
- -n → Does not output the trailing new line.
- -e → Enables interpretation of the backslash
- -E → Disables interpretation of the backslash
58. sed
The sed command is used to work in a stream editor called Sed in Linux. Sed editor can make basic text transformations in a file. With the help of the sed command, you can edit text files without opening files.
Syntax
sed [OPTION]... [COMMAND] [FILE]Useful Options
- -i → Modifies and saves the original file.
- -v → Displays version information, and exit.
59. Make
The make command in Linux can build any program from the terminal by compiling or recompiling the pieces of a large program where necessary.
Syntax
make [OPTION]... [TARGET]...Useful Options
- -b, -m → Options are used to ignore for compatibility with other versions of the make.
- -B, –always-make → Forces a rebuild of all targets, ignoring any existing dependencies and any files already built.
- -f=file, –file=file, –makefile=FILE → Ensures the usage of the file as a makefile.
- -e, –environment-overrides → Gives variables taken from the environment precedence over variables from makefiles.
- -i, –ignore-errors → Ignores all errors in commands executed to remake files.
- -k, –keep-going → Used to continue as much as possible after an error. While the target that failed, and those that depend on it, cannot be remade, the other dependencies of these targets can be processed as well.
- -R, –no-builtin-variables → Doesn’t define any built-in variables.
- -s, –silent, –quiet → Does not print the commands as they are executed.
- –warn-undefined-variables → Warns when an undefined variable is referenced.
- –trace → Prints the information about the disposition of each target.
60. xargs
The xargs command in Linux is a helpful tool for processing large lists of inputs and executing commands for each item in the list. It allows you to efficiently process inputs from other commands and automate repetitive tasks.
Syntax
xargs [OPTION]... [COMMAND [INITIAL-ARGUMENTS]]Useful Options
- -a, –arg-file=FILE → Reads input from a file instead of standard input.
- -I, –replace[=STRING] → Replaces occurrences of a string with the arguments passed to xargs.
- -L, –max-lines=NUM → Passes no more than NUM arguments to each invocation of the command.
- -n, –max-args=NUM → Passes no more than NUM arguments to each invocation of the command.
- -p, –interactive → Prompts the user for confirmation before executing each command.
- -r, –no-run-if-empty → Does not run the command if the input is empty.
- -s, –max-chars=NUM → Passes no more than NUM characters to each invocation of the command.
- -t, –verbose → Prints the command line before executing it.
61. exec
The exec command replaces the current terminal process with a new command that takes over the memory, process ID, and some other resources. This command in Linux is often used to execute specific programs or commands without creating a new process. If the exec command is executed without any other command, it terminates the terminal. So, the bash command needs to be executed before that.
Syntax
exec [OPTION]... [ARGUMENT]...Useful Options
- -c → Executes command with an empty environment.
62. awk
The awk command in Linux is a scripting language. It is used for text processing, data manipulation, and report generation while working in the command line. The awk allows the user to use variables, numerical functions, string functions, and logical operators without further compilation. It enables a programmer to develop a precise but impactful script that can do a specific task for the matched line of every record inside a file.
Syntax
awk '{action}' [file_name.txt]Useful Options
- -F value → Sets the field separator, FS, to value.
- -f file → Program text is read from the file instead of from the command line. Multiple -f options are allowed.
- -v var=value → Assigns a value to program variable var.
63. sort
The sort command in Linux is used to sort lines of text files. It is capable of sorting alphabetically and numerically, in ascending or descending order. It considers all contents as ASCII and rearranges them based on ASCII value.
Syntax
sort [OPTION]... [FILE]...Useful Options
- -f, –ignore-case → Makes sort case insensitive.
- -M, –month-sort → Sorts by month.
- -n, –numeric-sort → Compares based on the numerical value.
- -R, –random-sort → Shuffles the contents of the file.
- -r, –reverse → Reverses the comparison.
- -c, –check → Checks whether a file is sorted or not.
- -k, –key → Sorts by key.
- -o, –output → Used to print output in another file.
- -u, –unique → Removes duplicates excluding unique.
64. cut
The cut command in Linux is a utility tool for extracting a range of information from a file. Using the command you can slice texts based on byte/s, character/s, field/s, or delimiters. You can apply these parameters with the help of the options. You must type at least one of the available options after the cut command. Otherwise, the system will show error messages.
Syntax
cut OPTION... [FILE]...Useful Options
- -b, –bytes → Extracts only these bytes from the file.
- -c, –characters → Extracts only these characters from a file.
- -d, –delimiter → Extracts contents between assigned delimiters from a file.
- -f, –fields → Extracts only these fields from a file.
The options above mentioned accept only one type of range at a time. Types of ranges are defined as follows:
- N- → Extracts only the Nth integer, counting starts from 1.
- N-M → Extracts from the Nth integer to the Mth integer.
- M- → Extracts from the Mth integer to the end of the file.
65. paste
The paste command in Linux is a helpful tool for merging lines from multiple files. It takes input from multiple files and pastes the corresponding line together, separated by a delimiter. This command is very useful for merging columns of data from multiple files to a single file for further processing.
Syntax
paste [OPTION]... [FILE]...Useful Options
- -d, –delimiters=LIST → Reuses characters from LIST instead of TABs.
- -s,–serial → Pastes one file at a time instead of in a parallel manner.
- -z, –zero-terminated → Merges files separated by a NULL character instead of a newline character.
66. nano
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.
Syntax
Simply open any file in the nano editor using,
nano [OPTION]... [FILE]...Or, you can put the cursor on a specific line(or column) by adding the line number ( or column ) with a plus (+) sign. You can also make the string case insensitive by adding “c” or “r” followed by a plus(+) sign. For that, use the syntaxes,
nano [options] [[+line[,column]] file]...nano [options] [[+[crCR](/|?)string] file]...Useful Options
- -l, –linenumbers → Shows line numbers on the left.
- -m, –mouse → Enables mouse support.
- -v, –view → Open a file in read-only
- -i, –autoindent → Indents a new line automatically.
- -e, –emptyline → Keeps line below title bar blank.
- -g, –showcursor → Makes the cursor visible.
67. diff
The diff command in Linux compares files line by line. It can also differentiate between the contents within directories.
Syntax
diff [OPTION]... FILESUseful Options
- -B → Ignores blank lines.
- -c → Displays copied context.
- -i → Ignores case differences.
- -r → Recursively compares subdirectories.
- -s → Reports if files are identical.
- -q → Reports if files are different.
- -u → Displays unified context.
- -w → Ignores all white spaces.
- -y → Displays results in two columns.
68. patch
The patch command in Linux updates any source code of any program by identifying the data that needs to be changed/updated from a new file.
Syntax
patch [OPTIONS] [ORIGINAL_FILE] [PATCHFILE]Useful Options
- -b, –backup → Creates backup files. When patching a file, rename or copy the original instead of removing it.
- -c, –context → Specifies the number of context lines to be included in the patch file.
- -d dir, –directory=dir → Changes to the directory “dir” immediately before doing anything else.
- -D define, –ifdef=define → Uses the #ifdef … #endif constructs to mark changes, with define as the differentiating symbol.
- –dry-run → Prints the results of applying the patches without changing any files.
69. wc
The “wc” of the wc command comes from “Word Count”.It shows the word count, character count, and the number of lines of file/files provided to it as an argument.
Syntax
wc [OPTION]... [FILE]...Useful Options
- -w, –words → Displays the word counts.
- -l, –lines → Shows the line counts.
- -m, –chars → Displays the character counts.
- -c, –bytes → Shows the byte counts.
- -L, –max-line-length → Prints the length of the longest line.
- –files0-from → Takes input from the files specified by Nul-terminated names in a file.
70. tee
The tee command in Linux is used to read standard input and write to another file apart from standard output. This command is very useful to store the intermediate output of multiple commands.
Syntax
tee [OPTION]... [FILE]...Useful Options
- -a → Appends output to the given files.
- -i → Ignores Interruptions.
- -p → Diagnoses errors in writing to non-pipe output.
71. ln
The ln command in Linux is used to create links (shortcuts) to the source file/directory. There are two types of links and these are hard links & symbolic links. When a file is linked with a hard link, if you make any changes to any of the files this will reflect on both files whereas when a file is linked with a symbolic link if any of the files/directories are moved or deleted, this will break the link between the files.
Syntax
ln [OPTION]... [SOURCE_FILE] [LINKED_FILE]Here, SOURCE_FILE represents the name of the source file, and LINKED_FILE denotes the name of the linked file created with the ln command.
Useful Options
No option is needed to create a hard link to the file.
- -s → Creates symbolic links to files/directories.
- -b → Creates a backup of the file.
72. which
The which command in Linux can locate a command if it is passed as an argument. It takes the argument and searches for the corresponding name in the $PATH environment variable of executable files.
Syntax
which [OPTION] filename...Useful Options
- -a → Prints all the locations of each command.
73. uptime
The uptime command in Linux provides helpful information about the amount of time the system has been running, the number of users currently logged in, and the system load averages for a specified period.
Syntax
uptime [OPTION]...Useful Options
- -p, –pretty → Shows uptime information in a human-readable format.
- -h, –help → Displays this help page
- -s, –since → Prints the date and time since the system has been up, in yyyy-mm-dd HH:MM:SS format.
74. file
The file command in Linux tests each file passed as an argument to determine its classification. During the process, the system runs three types of tests and the succeeding test determines the file type.
The descriptions of these tests are given below.
- filesystem test: Checks whether the file is empty or if it is of a special type. The test examines the return from a stat(2) system call.
- magic test: Checks for files with fixed data formats. It uses the concept of “magic number” that indicates extensions of data files.
- language test: Determines in what language the file is written. It looks for a particular string that can appear anywhere in the first few blocks of the file.
Syntax
file [OPTION]... FILE…Useful Options
- -b → Does not print filenames with output.
- -c → Prints out the parsed form of the file.
- -d → Shows debugging information of a file.
- -f → Reads file names from a name file.
- -i → Gives mime-type strings as output.
- -s → Determines the type of special files.
- -z → Determines the type of compressed files.
75. finger
In Linux, the major objective of the finger command is to display the users’ login information on a system. This command helps to display the idle status of the user. It can also be used to display the user’s plan and project. The information provided by the finger command may vary depending on the system configuration.
Syntax
finger [OPTION]... [USERNAME]...Useful Options
- -p → Shows information except for the user’s plan or project.
- -s → Displays idle status with login information.
- -m → Prevents matching of user names.
76. users
The user command is a utility tool to find the names of all users who are currently logged in to the system.
Syntax
users [OPTION]... [FILE]Useful Options
- –help → Displays the help section of the users
- –version → Displays the version information of the users
77. groups
A group is a collection of users in Linux that helps to manage multiple users with the same security and privileges. Moreover, One user can be part of multiple groups. The groups command in Linux allows users to see which groups they and other users belong to.
Syntax
groups [OPTION]... [USERNAME]...Useful Options
- –help → Offers a brief description of the groups command and links to resources that are related.
- –version → Provides the version details of the groups command.
78. passwd
The passwd command in Linux is used for changing user passwords. The word passwd is used as a short form of Password.
Syntax
passwd [OPTIONS] [USER]Useful Options
- -a, –all → Shows the status of all users.
- -d, –delete → Deletes user password. The user account becomes unprotected.
- -h, –help → Display help message and exit.
- -e, –expire → Immediately makes the user password
- -i, –interactive → Make an account inactive after password expiration.
79. useradd
The useradd command is a Linux utility that allows you to create new user accounts on the system.
Syntax
useradd [OPTION]... user_nameUseful Options
- -c → Specify a comment or description for the user account.
- -d → Sets the user’s home directory.
- -D → Sets the user default value.
- -e,–expiredate → Sets the date on which the user account will be disabled.
- -f,–inactive → Sets password inactivity period of the new account.
- -g,–gid → Sets the user’s primary group.
- -G,–groups → Sets the user’s secondary groups.
- -h,–help → Displays the help message.
- -m → Creates the user’s home directory if it does not already exist.
- -M → Does not create the user’s home directory.
- -p,–password → Encrypted password of the new account.
- -r,–system → Creates a system account.
- -s → Sets the user’s login shell.
80. userdel
The userdel command in Linux is used for deleting user accounts on a system. It helps to manage user accounts and maintain the security of the system. The userdel command can help to remove an old or unused user account or to clean up your system by removing unnecessary accounts.
Syntax
userdel [OPTION]... USER_NAMEUseful Options
- –f, –force → Force removal of files, even if not owned by the user.
- -h, –help → Displays the help message.
- -r, –remove → Removes the home directory and all traces of the user from the system.
- –R, –root CHROOT_DIR → Allows you to specify a directory to chroot into before performing the user deletion, which can be useful for separate partition or filesystem cases.
- -Z, –selinux-user → Removes any SELinux user mapping for the user. SELinux is a security module that provides fine-grained security policies for Linux systems.
81. usermod
The usermod command is used to modify the attributes of an existing user. This command allows the root user or superuser to modify the user name, user ID, groups, home directory, password, user shell, expiry date, and other user details of an existing user. Generally, the usermod command provides the opportunity to modify the files like /etc/group, /etc/shadow, /etc/gshadow, /etc/login.def & /etc/passwd.
Syntax
usermod [OPTION]... USERUseful Options
- -a, –append → Adds the user to one or more supplementary groups. You can use it only with the option -G.
- -b, –badnames → Permits non-compliant names.
- -c, –comment → Adds comment field for the user account.
- -d, –home → Modifies the login directory for any existing user account.
- -e, –expiredate → Sets account expiry date. The date is specified in the format YYYY-MM-DD.
- -f, –inactive → Sets the number of days after a password will expire until the account is permanently disabled.
- -g, –gid → Changes the primary group for a User.
- -G, –groups → Adds supplementary groups.
- -l, –login → Changes the login name from user_name to new_user_name.
- -L, –lock → Locks the user’s password.
- -m, –move-home → Moves the contents of the home directory from the existing home directory to the new directory.
- -o, –non-unique → Allows to change the user ID to a non-unique value.
- -p, –password → Allows to specify the new unencrypted password.
- -R, –root CHROOT_DIR → Applies changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.
- -s, –shell → Specifies the user’s new login shell.
- -u, –uid → Specifies the new numerical value of the user’s ID.
- -U, –unlock → Unlocks a user’s password.
82. groupadd
The groupadd command in Linux allows administrators to create new user groups to manage privileges and permissions for multiple users more easily. This command helps to avoid the time-consuming task of setting permissions and privileges for each user individually, which can also be prone to errors.
Syntax
groupadd [OPTION]... GROUP_NAMEUseful Options
- -f, –force → Exits with success status if the specified group already exists, and turns off -g if specified GID already
- -g, –gid GID → Specifies the numerical value of the group’s ID, which must be unique unless -o is used and must be non-negative.
- -K, –key KEY=VALUE → Overrides /etc/login.defs defaults with specified KEY and VALUE, multiple -K options can be used.
- -o, –non-unique → Allows adding a group with a non-unique
- -p, –password PASSWORD → Sets an encrypted password for the group, the default is to disable the password.
- -r, –system → Creates a system group.
- -R, –root CHROOT_DIR → Specifies a different root directory than the default root directory
- -P, –prefix PREFIX_DIR → Specifies a different prefix than the default prefix to use when creating a new group.
83. addgroup
The addgroup command in Linux is used to create a new group on the current machine. It allows you to customize the group’s settings and manage privileges and permissions. It is similar to the groupadd command but more interactive than that.
Syntax
addgroup [OPTION]... GROUP_NAMEUseful Options
- –debug → Enables debugging mode.
- –force-badname → Allows you to create a group with a name that does not match the system’s naming conventions.
- –gid GID → Specifies the numerical value of the group’s ID, which must be unique and non-negative.
- -h, –help → Displays help message.
- –system → Creates a system group.
84. groupmod
The groupmod command is used to modify the attributes of an existing group. This command allows the root user or superuser to modify the group name, GID, password, and other important information of an existing group. Moreover, it provides the opportunity to modify files like /etc/group, /etc/gshadow, /etc/login.def & /etc/passwd.
Syntax
groupmod [OPTION]... GROUP_NAMEUseful Options
- -g, –gid → Changes the GID of a given group.
- -n, –new-name → Changes the name of an existing group.
- -p, –password → Enables password modification.
- -o, –non-unique → Allows changing the group GID to a non-unique
- -R, –root CHROOT_DIR → Applies changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.
85. screen
The screen command in Linux is used to run multiple sessions in a single terminal. For instance, you are working on a server remotely and you have only one terminal. But you want to run multiple processes simultaneously. The screen command makes it possible. Moreover, it minimizes the chances of abruptly closing a task midway that might be sensitive or takes a lot of time to complete.
Syntax
screen [OPTION]... [COMMAND [ARGUMENT]]...Useful Options
- -S → Creates a new session.
- -p → Assigns a password to a session.
- -X → Executes commands inside a session.
- -r → Reattaches to a session.
- -ls → Lists out all the running sessions.
86. apt
The apt command in Linux stands for “Advanced Package Tool”. It is a command-line interface for managing the packages on a user’s system. You can perform several actions including installation, update, and removal of packages with this command. You must use the sudo command along with apt to get root permissions while managing packages on your machine.
Syntax
apt command pkg…Useful Options
- -d, –download-only → Downloads a package but does not install.
- –only-upgrade → Upgrades a specific package.
- –installed → Returns only installed packages.
- –upgradeable → Returns only upgradeable packages.
- -y → Answers “yes” to prompt without interruption.
87. apt-get
The Advanced Package Utility (APT) library may be accessed via the command line tool apt-get (a package management system for Linux distributions), as it serves as the user’s “back end” for other programs that utilize the APT library. Anyway, you may use the apt-get command in Linux to find, install, manage, update, and uninstall applications.
Syntax
apt-get [OPTION] [COMMAND]Useful Options
- –auto-remove or –autoremove → When using apt-get with the install or remove command, this option acts like running the autoremove command.
- -d or –download-only → Specifies that apt-get should only retrieve the packages, and not unpack or install them.
- -f or –fix-broken → Specifies that apt-get should attempt to correct the system with broken dependencies in place.
- –no-install-recommends → Not to consider recommended packages as a dependency to install.
88. getent
The getent command in Linux is a tool that enables the retrieval of data from system databases such as passwd, group, and services. It can be utilized to either list all entries in a database or obtain information about a specific entry.
Syntax
getent [OPTION]... database key...Useful Options
- -s, –service: Specifies the service.
- -i, –no-idn: Disables IDN encoding in lookups.
- -?, –help: Show user help page.
- –usage: Display usage information.
89. source
The source command in Linux executes commands from the file passed as an argument to it in the current shell environment. This command is beneficial for sourcing a script that sets variables, functions, or aliases in the current shell session.
Syntax
source filename [argument]Useful Options
The source command in Linux is a shell built-in command. There is no option available for this command. To know more about this command, you can check its help page by executing the below command.
help source90. service
The service command in Linux is mainly used for starting, stopping, and restarting services on our operating system. This command is very versatile in controlling our system services.
Syntax
service [OPTIONS] [Service_Name] [COMMAND]Here, the Service_Name means the process running in the operating system, and COMMAND is the specific task you want to do.
Useful Options
- –status-all → Prints all available services on the terminal
- –help/-h → Prints the help section of the service command.
- –version → Shows the version of the service command.
91. jobs
The jobs command is used to display a set of jobs that are currently running in the background & the foreground in Linux. If the command prompt does not show any information that means no jobs are running at that time. By using the jobs command, you can see the process ID, job number & status of each Job.
Syntax
jobs [OPTION]Useful Options
- -l → Displays the process ID, job number, and status of each job
- -n → Displays only jobs that have changed status since the last notice.
- -p → Displays only the process ID of each job.
- -s → Displays the jobs that are stopped.
- -r → Displays the jobs that are running.
- -x → Executes command in the background.
92. htop
The htop command when used shows a list of all the running processes throughout the system. The htop command in Linux does the same function as the top command. But the difference is htop is more modern than the top. The htop command is more interactive than the top command.
Syntax
htop [-dCFhpustvH]Useful Options
- -u, –user → Only shows processes for a specific user.
- -M, –no-mouse: → Disables the interactive mouse operation.
- –tree → Shows system processes as a tree view.
93. at
The at command in Linux is a Command line utility tool used for scheduling one-time jobs. Users can specify a time for executing certain tasks. The command can also list or delete jobs that are saved for later execution. The atq, atrm, and batch commands are also part of the at command that enables it to queue, examine or remove scheduled jobs.
- at: Execute commands at the specified time.
- atq: List current users’ pending jobs.
- atrm: Remove pending job specified by job ID.
- batch: Runs commands when system load levels permit. By default, if the load average is below 1.5. And by 1.5 means, the system is 100% busy running 1 process while there is another process in the queue waiting to use 50% of the system.
Syntax
at [OPTION]... runtimeUseful Options
- -b → Runs commands when system load levels permit, an alias for batch.
- -c → Displays specified job context on the terminal.
- -f → Reads jobs from a file.
- -r/-d → Removes pending job specified by job ID, an alias for atrm.
- -l → Lists current users’ pending jobs, an alias for atq.
- -m → Mails user upon completion of the job.
- -M → Does not mail the user upon completion of the job.
94. cron
The cron command in Linux allows users to schedule commands to be repeated at a certain period. It recurrently matches the assigned time to the current time field. When there is a match the system executes given commands. cron is automatically started from /etc/init.d on entering multi-user run levels.
Syntax
cron [-f] [-l] [-L loglevel]Useful Options
- -f → Process stays in the foreground, and does not daemonize.
- -l → Enables LSB-compliant names for /etc/cron.d
- -n → Includes the FQDN in the subject when sending emails.
- -L loglevel → These levels are,
- 1 (Strats log of all cron jobs).
- 2 (Ends log of all cron jobs).
- 4 (Logs every failed job. Exit status is not equal to zero).
- 8 (Logs the process number of all cron jobs).
95. crontab
The crontab command in Linux is used for scheduling tasks at regular intervals. You can add your desired commands/scripts to crontab files by creating an editing session. The listed jobs in the crontab files are run by the cron daemon at predefined times.
Syntax
crontab [ -u user ] filecrontab [ -u user ] [ Option ]Useful Options
- -u → Specify the user name whose crontab file is accessed.
- -e → Edit current crontab using the specified editor.
- -l → Display/List current crontab on the standard output.
- -r → Remove current crontab.
- -i → Ask before removing crontab using -r.
96. uniq
The uniq command helps to detect any duplicate entity inside a text file to avoid redundancy.
Syntax
uniq [OPTION]... [INPUT [OUTPUT]]Useful Options
- -c, –count → Sets a prefix at the start of the lines by the number of occurrences.
- -d, –repeated → Prints the duplicate lines, one for each group.
- -D → It prints all the duplicate lines.
- -f, –skip-fields=N → Avoids comparing the first N fields.
- -i, –ignore-case → Ignores the differences in the case when comparing.
- -u, –unique → Prints the unique lines.
97. dig
The dig command in Linux is a network administration command-line tool that stands for Domain Information Groper. It is used to gather DNS ( Domain Name System) information. The command performs tasks related to DNS lookups to query DNS name servers. Mainly it is used by network administrators to verify and troubleshoot DNS problems.
Syntax
dig [server] [name] [type]Here,
- Server ⟶ The name or IP address of the name server whom we want to query. If you don’t specify a server, the dig command will use your machine’s pre-configured DNS.
- Name ⟶ It is the name of the resource record that is to be looked up using the DNS name server.
- Type ⟶ The type of query or DNS record you are looking for. The type argument must be valid. If no type argument is applied, the dig command performs a lookup on the A record by default.
Some Common DNS record types:
- A ⟶ Address records are one of the basic and most commonly used records, which are used to directly map a hostname to an IP Address. They translate domain names and store them as IP addresses. Address records can only hold IPv4 addresses.
- MIX⟶ Stands for Mail Exchange. Which maps message transfer agents for the domain. It stores instructions to direct emails to mail servers.
- SIG⟶ SIG for the SIGnature record, used for encryption protocol.
- TXT ⟶TeXT records are used to store definitive text.
- CNAME ⟶ ( Canonical NAME) record type is used instead of an A (Adress) record if a domain is an alias for another domain.
- SOA ⟶( Start Of Authority) record type holds important information about a domain or zone.
NS ⟶ (Name Server) record contains the authoritative name servers.
Useful Options
- -4 → Used for IPv4 only.
- -6 → Used for IPv6 only.
- -b address → Sets the source IP address of the query.
- -c class → Sets the query class.
- -f file → Used for Batch mode. The dig command gets lookup requests from the specified files and processes each line systematically as they are organized in the file.
- -i → Used for reverse IPv6 lookups.
- -m → Used to enable memory usage debugging.
- -u → DIsplays the query time in microseconds.
- -v → Displays the version information.
- -x → Reverses lookups for mapping the addresses to names.
- -t type → Specifies the resource record type to query.
98. nslookup
The nslookup is a network-administrator command tool that stands for Name Server Lookup. It performs queries on DNS (Domain Name System) to obtain domain names, IP address mapping, or any other specific DNS record. We mainly use the nslookup command to troubleshoot DNS-related problems.
Syntax
The syntax for interactive mode is,
nslookup [OPTION]... [Name | -] [Server]And the syntax for non-interactive mode is,
nslookup [OPTION]... <Domain_Name>Here,
- OPTION⟶ OPTIONs are used to modify the nslookup
- Domain Name ⟶ The name or IP address of the name server whom we want to query. If you don’t specify a server, the nslookup command will use your machine’s pre-configured DNS.
Useful Options
Interactive Options:
- host [server] → Looks up information for the host using the default or specified server.
- server domain → Looks up information about the domain using the default server.
- Iserver domain → Looks up information about the domain using the initial server.
- set keyword [=value], → Changes state information that affects the lookups (=all, to display the current values of the frequently used options to set)
- domain=name → Sets the search list to name.
- class =value → Changes the query class to one of these values, such as (IN (INternet), CH(CHaos), HS(HeSiod), ANY(wildcard)). The default is IN.
- port=value → Changes the default TCP/UDP name server port to value, default is 53.
- type=value → (a, any, cname, gid, hinfo, mb, mg, minfo, mr, mx, ns, ptr, soa, txt)
- retry=number → Sets the number of retries to a number.
- timeout=number → Sets the initial timeout interval for waiting for a reply, in seconds.
- [no]debug, to turn on or off the display of the full and intermediate response packets while searching. The default in nobug.
- [no]d2 → Turns on or off the debugging mode.
- [no]recurse → Tells the name server to query other servers if it does not have the information.
- [no]fail → Tries the next nameserver if a name server responds with SERVFAIL. The default is nofail.
- exit, to exit the program.
Non-Interactive Options
- -domain=[domain-name] → Changes the default DNS name.
- -debug, show debugging info.
- -port=[port-number], → Changes the standard port
- -timeout=[seconds] → Specifies the time for the server to respond.
- -type=a → Displays all the info about DNS A
- -type=any → Displays info about all types of DNS
- -type=hinfo → Prints hardware-related information about the host.
- -tpe=ns → Displays Name Server
- -type=mx → Displays all the info about DNS Mail Exchange
- -type=ptr → Displays Pointer Records.
- -type=soa → Displays Start Of Authority
Some Common DNS record types:
- A ⟶ Address records are one of the basic and most commonly used records used to map a hostname to an IP Address directly. They translate domain names and store them as IP Address records that can only hold IPv4 addresses.
- MX⟶ Stands for Mail Exchange. Which maps message transfer agents for the domain. It stores instructions to direct emails to mail servers.
- SIG⟶ SIG for the SIGnature record, used for encryption
- TXT ⟶TeXT records are used to store definitive text.
- CNAME ⟶ ( Canonical NAME) record type is used instead of an A (Adress) record if a domain is an alias for another domain.
- SOA ⟶( Start Of Authority) record type holds important information about a domain or zone.
- NS ⟶ (Name Server) record contains the authoritative name servers.
99. netstat
The netstate command in Linux is a network display command tool that stands for Network Statistics. It displays all the network-associated information such as the list of all the network connections on the system, routing tables, interface statistics, multicast memberships, masquerade connections, etc. The command can also display the current state of a network interface, like its IP address, netmask, and status.
Syntax
netstat [OPTION]...Useful Options
- -a, –all → Displays all active connections.
- -at → Displays all active TCP
- -au → Displays all active UDP
- -l, –listening → Displays only listening ports.
- -M, –masquerade → Displays all masquerade connections.
- -r, –route → Prints the kernel routing tables.
- -g, –groups → Displays multicast group membership information.
- -i, –interfaces → Displays all network interfaces.
- -ie → Displays the statistics for a specific network interface.
- -s, –statistics → Displays the summary statistics of each protocol.
- -st → Displays the statistics of TCP
- -su → Displays the statistics of UDP
- -c, –continuous → Prints netstat information continuously.
- -n, –numeric → Displays numeric addresses defining symbolic hosts, ports, or usernames.
- -v, –verbose → Displays the detailed output.
- -A, –protocol=family → Specifies the address families for which connections are to be displayed.
- -e, –extend → Displays extended output.
- -o, –timers → Includes networking timers-related information.
- -p, –program → Displays the PID and name of the process of the corresponding sockets.
- -C → Displays the routing information from the route cache.
100. neofetch
The neofetch command is an easy and super fast command line tool to fetch system information such as the hostname, operating system, kernel version, and desktop environment in an artistic and visually charming way within seconds.
Syntax
neofetch <func_name> [OPTION]... “value”Here,
- func_name → It specifies a function name to quickly display that function’s information. Which is the second part of the information on the display configuration.
- Options → Options are used to modify and increase the usage of the command in a user-friendly way.
- Value → These are the values that we assign to our options to modify the command.
Useful Options
Info
- –disable infoname → Disables an info line from appearing in the output. Where infoname is the function name that can be memory, disk, hostname, shell, or any info you want to disable.
- –cpu_brand on/off → Enables or disables CPU brand in the display.
- –cpu_speed on/off → Shows/hides the CPU speed.
- –cpu_temp C/F/off → Shows/hides CPU temperature.
- –cpu_brand on/off → Shows/hides CPU bran.
Text formatting
- –colors x x x x x x → Changes the text colors in this order.
- –underline on/off → Enables/disables the underline.
- –bold on/off → Enables/disables bold text.
Color Blocks
- –color_blocks on/off → Enables/disables the color blocks.
- –col_offset auto/num → For eft-padding of color blocks.
- –block_width num → Sets the width of color blocks in spaces.
- –block_height num → Sets the height of color blocks in lines.
BARS
- –bar_char ‘elapsed char’ ‘total char’ → Characters to use when drawing bars.
- –bar_border on/off → Surrounds the bar with [ ] or not.
Conclusion
Exhale! You have reached the end of this long list of commands. After completing this huge article, you will cover almost 90% of the commands you will need to master for the CLI of Linux. Hope this article helps! Happy exploring and command-line empowerment!
