Ubuntu Most Used CLI (Terminal) Commands

DATE

The simple “date” command displays the current date and time (including the day of the week, month, time, time zone, year).

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”.

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)”

Date -d

To operate the system on a specific date, you can change the date by using “-d”.
Syntax: date -d Date_to_operate_system_on

date

TZ=GMT date

TZ=America/New_York date

sudo date --set="20230519 22:10"

date -d now
date -d yesterday
date -d tomorrow
date -d last-Sunday
date -d "1997-04-22"

$ 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

$ date -d now
Thu Mar  2 07:36:55 PM EST 2023
$ date -d yesterday
Wed Mar  1 07:37:00 PM EST 2023

 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.
Syntax: df

The command “df -h” shows the same result as the command “df” but now the data is in a more human-readable form that can be easily comprehended by a new user.
Syntax: df -h

df
df -h

$ df
Filesystem                  1K-blocks       Used  Available Use% Mounted on
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
192.168.1.1:/media/TR-004 11627352064 9633692672 1407599616  88% /media/tim/TR-004
192.168.1.1:/ubuntu-data    959776768  657463296  253486080  73% /media/tim/ubuntu01-data
192.168.1.11:/home/tim      479593984   21986816  433171968   5% /media/hass-srv
tmpfs                         1623280        288    1622992   1% /run/user/1000

$ 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
192.168.1.1:/media/TR-004   11T  9.0T  1.4T  88% /media/tim/TR-004
192.168.1.1:/ubuntu-data   916G  628G  242G  73% /media/tim/ubuntu01-data
192.168.1.11:/home/tim     458G   21G  414G   5% /media/hass-srv
tmpfs                      1.6G  288K  1.6G   1% /run/user/1000

FREE

The command “free” displays the amount of free and used memory in the complete system.
Syntax: free

free

$ free
               total        used        free      shared  buff/cache   available
Mem:        16232804    10545772      978552      125388     4708480     5252532
Swap:        2097152     2090408        6744

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).
Syntax: 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:

UID PID PPID C STIME TTY TIME CMD

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND

ps
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.
Syntax: uptime

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.
Syntax: w

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.
Syntax: passwd user_name

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.
Syntax: exit

exit

$ exit
logout
Connection to 192.168.1.1 closed.

SHUTDOWN

The command “shutdown” is used to shut down the system.
Syntax: shutdown

shutdown

$ shutdown
Shutdown scheduled for Thu 2023-03-02 20:12:13 EST, use 'shutdown -c' to cancel.

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

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

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 inadvertantly delete your whole drive!

mkdir NewDirectory
rmdir DirectoryName
rm -rf /path/to/dir/name

mkdir docs
rmdir docs