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Command Name & Description
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Command(s)
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Notes / Sample Output
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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 operatesee the system onday and time for a specific date, you can change the date by using “-d”.
Syntax: date -d Date_to_operate_system_on
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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"
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$ 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
< This command example would set the system's date and time to May 19, 2023 10:10pm
$ date -d now
Thu Mar 2 07:36:55 PM EST 2023
$ date -d yesterday
Wed Mar 1 07:37:00 PM EST 2023
$ date -d "1997-04-22"
Tue Apr 22 12:00:00 AM EDT 1997
If using a specific date for date -d, you must place the date you want in the format YYYY-MM-DD
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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
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df
df -h
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$ 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
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FREE
The command “free” displays the amount of free and used memory in the complete system.
Syntax: free
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free
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$ free
total used free shared buff/cache available
Mem: 16232804 10545772 978552 125388 4708480 5252532
Swap: 2097152 2090408 6744
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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
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ps
ps -ef
ps -aux
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$ 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]
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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
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uptime
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$ uptime
19:59:06 up 22 days, 20:17, 1 user, load average: 0.52, 0.39, 0.38
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W
The command “w” displays detailed information about the users who are logged into the system currently.
Syntax: w
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w
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$ 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
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PASSWD
The command “passwd” stands for password and it is used to change the password of the user.
Syntax: passwd user_name
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passwd my_user
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$ passwd tim
changing password for tim.
(current) UNIX password:
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
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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
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exit
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$ exit
logout
Connection to 192.168.1.1 closed.
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SS
The ss command is a modern replacement for the classic netstat. You can use it on Linux to get statistics about your network connections.
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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 )'
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SHUTDOWN
The command “shutdown” is used to shut down the system.
Syntax: shutdown
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shutdown
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$ shutdown
Shutdown scheduled for Thu 2023-03-02 20:12:13 EST, use 'shutdown -c' to cancel.
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