Commands

Most frequently used CLI (Terminal) commands on Linux

Commands used for System Information
Commands used for File Handling

Commands used for System Information

Command(s)	Sample Output
DATE The simple “date” command displays the current date and time (including the day of the week, month, time, time zone, year). `date` Date TZ By default, “date” command uses the time zone defined in path “/etc/localtime”. Linux user can change the time zone via Terminal by using command “TZ”. `TZ=GMT date` `TZ=America/New_York date` Date --set Linux allows its user to set the current date and time of the system manually. Syntax: date –set=”Date_in_format(YYMMDD) Time_in_format(HH:MM)” `sudo date --set="YYYYMMDD HH:MM"`	`$ date Thu Mar 2 07:23:38 PM EST 2023 $ TZ=GMT date Fri Mar 3 12:03:59 AM GMT 2023 $ TZ=America/New_York date Thu Mar 2 07:04:12 PM EST 2023` Example - This would set the system date to May 18, 2023 10:10 PM `sudo date --set="20230519 22:10"`
DF The command “df” shows the amount of disk space used and disk space available on every file system containing each filesystem’s name and its path. `df` The command “df -h” shows the same result as the command “df” but now the data is in a more human-readable format. `df -h`	$ df Filesystem 1K-blocks Used Available Use% Mounted tmpfs 1623284 3612 1619672 1% /run /dev/nvme0n1p3 491343600 18123184 452739188 4% / tmpfs 8116400 104604 8011796 2% /dev/shm tmpfs 5120 4 5116 1% /run/lock tmpfs 8116400 0 8116400 0% /run/qemu /dev/nvme0n1p2 456036 182424 239424 44% /boot /dev/nvme0n1p1 98304 57271 41033 59% /boot/efi /dev/sda1 47744748 57156 45229840 1% /tmp /dev/sda3 2787016696 1123163768 1531975216 43% /home /dev/sda2 47745772 31301948 13986020 70% /var $ df -h Filesystem Size Used Avail Use% Mounted on tmpfs 1.6G 3.6M 1.6G 1% /run /dev/nvme0n1p3 469G 18G 432G 4% / tmpfs 7.8G 103M 7.7G 2% /dev/shm tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 7.8G 0 7.8G 0% /run/qemu /dev/nvme0n1p2 446M 179M 234M 44% /boot /dev/nvme0n1p1 96M 56M 41M 59% /boot/efi /dev/sda1 46G 56M 44G 1% /tmp /dev/sda3 2.6T 1.1T 1.5T 43% /home /dev/sda2 46G 30G 14G 70% /var
FREE The command “free” displays the amount of free and used memory in the complete system. `free`	`$ free total used free shared buff/cache available Mem: 16232800 4698636 6761664 59100 4772500 11205016 Swap: 2097152 0 2097152`
PS The command “ps” which is also known as the process status command is used to provide information about the processes currently running on the system, including their respective process identification numbers (PIDs) `ps` PS AUX & PS -EF Both list all processes of all users. In that aspect `-e` and `ax` are completely equivalent. Where they differ is output format specifier, `-f` is "full", while `u` is "user-oriented". The displayed columns are different: `ps -ef` `ps -aux`	`$ ps PID TTY TIME CMD 434765 pts/0 00:00:00 bash 441698 pts/0 00:00:00 ps` $ ps -ef UID PID PPID C STIME TTY TIME CMD root 1 0 0 Feb07 ? 00:19:03 /sbin/init splash root 2 0 0 Feb07 ? 00:00:03 [kthreadd] root 3 2 0 Feb07 ? 00:00:00 [rcu_gp] root 4 2 0 Feb07 ? 00:00:00 [rcu_par_gp] root 5 2 0 Feb07 ? 00:00:00 [slub_flushwq] root 6 2 0 Feb07 ? 00:00:00 [netns] $ ps -aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.0 169808 12472 ? Ss Feb07 19:03 /sbin/init splash root 2 0.0 0.0 0 0 ? S Feb07 0:03 [kthreadd] root 3 0.0 0.0 0 0 ? I< Feb07 0:00 [rcu_gp] root 4 0.0 0.0 0 0 ? I< Feb07 0:00 [rcu_par_gp] root 5 0.0 0.0 0 0 ? I< Feb07 0:00 [slub_flushwq] root 6 0.0 0.0 0 0 ? I< Feb07 0:00 [netns]
UPTIME The command “uptime” provides information about how long the system has been running in one line. The result for this command includes the current time, the time duration system has been running, the number of users who are currently logged on, and the system load averages for the past 1, 5, and 15 minutes respectively. `uptime`	`$ uptime 19:59:06 up 22 days, 20:17, 1 user, load average: 0.52, 0.39, 0.38`
W The command “w” displays detailed information about the users who are logged into the system currently. `w`	`$ w 20:00:25 up 22 days, 20:18, 1 user, load average: 0.44, 0.41, 0.38 USER TTY FROM LOGIN IDLE JCPU PCPU WHAT tim :1 :1 07Feb23 xdm 2days 0.00s /usr/libexec/gdm-x-session --run-script env`
PASSWD The command “passwd” stands for password and it is used to change the password of the user. `passwd my_user`	`$ passwd tim changing password for tim. (current) UNIX password: Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully`
EXIT The command “exit” as the name says it is used to exit from the system and log out from the current user. `exit`	`$ exit logout Connection to 192.168.1.1 closed.`
SS The ss command is a modern replacement for the classic netstat command. You can use it on Linux to get statistics about your network connections. Use the -ltn flags to list all listening ports on your system. `ss -ltn` Use the following to see if a specific port is listening on your system. In this case, the source port (sport) and destination port (dport) is 80 or you can use the protocol name, http, instead. `ss -a '( dport = :80 or sport = :80 )'` `ss -a '( dport = :http or sport = :http )'`	`$ ss -ltn State Recv-Q Send-Q Local Address:Port Peer Address:Port Process LISTEN 0 4096 0.0.0.0:9000 0.0.0.0:* LISTEN 0 4096 0.0.0.0:6767 0.0.0.0:* LISTEN 0 4096 0.0.0.0:111 0.0.0.0:* LISTEN 0 4096 0.0.0.0:80 0.0.0.0:` `$ ss -a '( dport = :80 or sport = :80 )' Netid State Recv-Q Send-Q Local Address:Port Peer Address:PortProcess tcp LISTEN 0 4096 0.0.0.0:http 0.0.0.0: tcp LISTEN 0 4096 [::]:http [::]:*`
SHUTDOWN The command “shutdown” is used to shut down the system. Note: The shutdown command needs superuser privileges. Hence, you should either be root or run the command with sudo. Using the command with no flags will schedule a shutdown 1 minute from execution. `sudo shutdown` Use the following to IMMEDIATELY shutdown your system. `sudo shutdown now` You can schedule a shutdown in future by providing the time argument either in +t format or in hh:mm format. For example, if you want to shutdown the system after 15 minutes, you can use this command: `sudo shutdown +15` If you want to shutdown the system at 6 PM in the afternoon, you can use it in the following manner: `sudo shutdown 18:00` Cancel a shutdown `sudo shutdown -c` Reboot a system `sudo shutdown -r` `sudo reboot`	`$ sudo shutdown Shutdown scheduled for Thu 2023-03-02 20:12:13 EST, use 'shutdown -c' to cancel.`

Commands used for File Handling

LS The command “ls” displays the list of all directories, folder, and files present in the current directory. LS - LTR The above-mentioned command displays the name of directories, folders, files with their respective owner name, group’s name, and rights your user has over these.	`ls ls -ltr`	`/$ ls bin dev lib libx32 mnt root snap sys usr boot etc lib32 lost+found opt run srv tim var cdrom home lib64 media proc sbin swapfile tmp` /$ ls -ltr total 2097256 drwxr-xr-x 2 root root 4096 Feb 9 2021 mnt drwxr-xr-x 15 root root 4096 Feb 9 2021 var drwx------ 2 root root 16384 Feb 11 2022 lost+found lrwxrwxrwx 1 root root 8 Feb 11 2022 sbin -> usr/sbin lrwxrwxrwx 1 root root 10 Feb 11 2022 libx32 -> usr/libx32 lrwxrwxrwx 1 root root 9 Feb 11 2022 lib64 -> usr/lib64 lrwxrwxrwx 1 root root 9 Feb 11 2022 lib32 -> usr/lib32 lrwxrwxrwx 1 root root 7 Feb 11 2022 lib -> usr/lib lrwxrwxrwx 1 root root 7 Feb 11 2022 bin -> usr/bin drwxrwxr-x 2 root root 4096 Feb 11 2022 cdrom drwx------ 10 root root 4096 Feb 12 2022 tim -rw------- 1 root root 2147487744 Aug 9 2022 swapfile drwxr-xr-x 5 root root 4096 Aug 14 2022 home drwxr-xr-x 14 root root 4096 Oct 22 14:08 usr drwxrwxrwx 7 root root 4096 Nov 26 04:18 media drwxrwxrwx 13 root root 4096 Jan 7 21:59 opt drwxr-xr-x 2 root root 4096 Feb 5 07:19 srv dr-xr-xr-x 13 root root 0 Feb 7 23:41 sys dr-xr-xr-x 549 root root 0 Feb 7 23:41 proc drwx------ 12 root root 4096 Feb 8 04:25 root drwxr-xr-x 20 root root 5120 Feb 17 23:04 dev drwxr-xr-x 28 root root 4096 Feb 21 23:36 snap drwxr-xr-x 168 root root 12288 Mar 1 06:24 etc drwxr-xr-x 5 root root 4096 Mar 2 06:51 boot drwxr-xr-x 46 root root 1500 Mar 2 20:11 run drwxrwxrwt 32 root root 20480 Mar 2 21:06 tmp
MKDIR The command “mkdir” allows users to create directories/folders in the system. The user running this command must have suitable rights over the parent directory to create a directory or they will receive an error. Syntax: mkdir New_Directory’s_Name	`mkdir NewDirectory`	`~$ mkdir poopoo ~$ ~$ ls Android Pictures AppImages poopoo`
RMDIR The command “rmdir” allows users to remove directories/folders from the system. The user running this command must have suitable rights over the parent directory to remove a directory AND the directory must not have any files or sub-directories within it or you will receive an error. Syntax: rmdir Directory’s_Name	`rmdir DirectoryName`	`~$ rmdir poopoo rmdir: failed to remove 'poopoo': Directory not empty # Could not delete directory # "poopoo" because it is not # empty ~$ rm poopoo rm: cannot remove 'poopoo': Is a directory # Could not remove "poopoo" # because it is not a file`
RM The command “rm” is used to remove files from a directory. RM -RF Permanently deletes the specified directory and ALL files and sub-directories beneath the specified directory. Be VERY careful using this command as you can inadvertently delete your whole drive!	`rm filename` `rm -rf /path/to/dir/name`	`# Listing shows poopoo.txt # file exists under # direcotry "poopoo" ~/poopoo$ ls poopoo.txt ~/poopoo$ rm poopoo.txt # listing now shows # poopoo.txt has been # removed (deleted) # from directory "poopoo" ~/poopoo$ ls ~/poopoo$` `# Directory "poopoo" exists # in the listing below ~$ ls Android Pictures AppImages poopoo Audio Public ~$ rm -rf poopoo ~$ # Successfully removed # "poopoo" directory # and all its contents # as can be seen in the # listing below ~$ ls Android Parkitect AppImages Pictures Audio Public`
MV The command “mv” is used for two purposes To move files or directories from one path to another path in the system. To rename a file or folder.	`mv Source_File_name Destination_File_Name` `mv File_name New_name_for_file`
CP The command “cp” is used to copy data from a source file to the destination file. Its function is almost like the command “mv”. The only difference is by using the command “cp” the source file is not removed from the directory after its data is moved to the destination file.	`cp source_file_name destination_file_name`
TOUCH Creates an empty file at the specified path with the specified name. Useful for creating a blank file you intend to edit with a CLI editor, such as VIM or NANO.	`touch /path/name/filename.ext`	`~$ ls doc.txt ls: cannot access 'doc.txt': No such file or directory ~$ touch /home/tim/doc.txt ~$ ls doc.txt doc.txt`
CAT The command “cat” is a reverse of the command “tac”. It is used to display each line of the file starting from the first row and finishing on its last row. This command is more frequently used than “tac”.	`cat file_name`
ECHO The command “echo” used to display any expression that is passed as an argument.	`echo expression_to_be_displayed`	`~/poopoo$ echo something-poopoo something-poopoo`
GREP The command “grep” is used to search for a text in the specified file/folder.	`grep “expression_to_be_Searched” file_name_to_search_in`
ZIP The command “zip” is used to compress one or more files and store them in a new file with .zip extension.	`zip new_zip_file_name.zip`	`~/poopoo$ zip files.zip file1.txt file2.txt file3.txt adding: file1.txt (stored 0%) adding: file2.txt (stored 0%) adding: file3.txt (stored 0%) ~/poopoo$ ls file1.txt file2.txt file3.txt files.zip`
UNZIP The command “unzip” is used to decompress a .zip file and extract all the files within to current directory.	`unzip zip_file_name.zip`	`~/poopoo$ unzip files.zip Archive: files.zip replace file1.txt? [y]es, [n]o, [A]ll, [N]one, [r]ename: A extracting: file1.txt extracting: file2.txt extracting: file3.txt`
SUDO Sudo stands for SuperUser DO and is used to access restricted files and operations. By default, Linux restricts access to certain parts of the system preventing sensitive files from being compromised. The `sudo` command temporarily elevates privileges allowing users to complete sensitive tasks without logging in as the root user. sudo -i elevates the user to root for the remainder of the session rather than a command by command basis.	`sudo some-command` `sudo -i`	# No directory called "peepee" # exists $ ls bin dev lib libx32 mnt root snap sys usr boot etc lib32 lost+found opt run srv tim var cdrom home lib64 media proc sbin swapfile tmp # Attempt to make directory # "peepee" as a noraml user # fails because I'm # trying to make the # directory in a path I # don't have rights to $ mkdir peepee mkdir: cannot create directory ‘peepee’: Permission denied # using SUDO to temporarily # elevate my privileges, I # can now create the # directory "peepee" # in the path as can be seen # in the listing below: $ sudo mkdir peepee [sudo] password for tim: $ ls bin dev lib libx32 mnt proc sbin swapfile tmp boot etc lib32 lost+found opt root snap sys usr cdrom home lib64 media peepee run srv tim var `~/poopoo$ sudo -i [sudo] password for tim: ~#`