# 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). ```shell 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”. ```shell 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" ``` `$ dateThu Mar  2 07:23:38 PM EST 2023$ TZ=GMT dateFri Mar  3 12:03:59 AM GMT 2023$ TZ=America/New_York dateThu Mar  2 07:04:12 PM EST 2023` Example - This would set the system date to May 18, 2023 10:10 PM ```shell 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. ```shell df ``` The command “df -h” shows the same result as the command “df” but now the data is in a more human-readable format. ```shell df -h ``` `$ dfFilesystem    1K-blocks       Used  Available Use% Mountedtmpfs         1623284       3612    1619672   1% /run/dev/nvme0n1p3 491343600   18123184  452739188   4% /tmpfs            8116400     104604    8011796   2% /dev/shmtmpfs               5120          4       5116   1% /run/locktmpfs            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 -hFilesystem     Size  Used Avail Use% Mounted ontmpfs           1.6G  3.6M  1.6G   1% /run/dev/nvme0n1p3  469G   18G  432G   4% /tmpfs           7.8G  103M  7.7G   2% /dev/shmtmpfs           5.0M  4.0K  5.0M   1% /run/locktmpfs           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. ```shell free ``` `$ free       total     used     free    shared  buff/cache   availableMem:  16232800  4698636  6761664 59100     4772500    11205016Swap:  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) ```shell 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: ```shell ps -ef ``` ```shell ps -aux ``` `$ ps    PID TTY          TIME CMD 434765 pts/0    00:00:00 bash 441698 pts/0    00:00:00 ps` `$ ps -efUID          PID    PPID  C STIME TTY          TIME CMDroot           1       0  0 Feb07 ?        00:19:03 /sbin/init splashroot           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 -auxUSER  PID %CPU %MEM VSZ  RSS TTY STAT START TIME COMMANDroot 1  0.0  0.0 169808 12472 ? Ss Feb07  19:03 /sbin/init splashroot    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. ```shell 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. ```shell w ``` `$ w 20:00:25 up 22 days, 20:18,  1 user,  load average: 0.44, 0.41, 0.38USER     TTY      FROM             LOGIN   IDLE   JCPU   PCPU WHATtim      :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. ```shell passwd my_user ``` `$ passwd timchanging 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. ```shell exit ``` `$ exitlogoutConnection 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. ```shell 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. ```shell ss -a '( dport = :80 or sport = :80 )' ``` ```shell ss -a '( dport = :http or sport = :http )' ``` `$ ss -ltnState   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. ```shell sudo shutdown ``` Use the following to IMMEDIATELY shutdown your system. ```shell 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: ```shell sudo shutdown +15 ``` If you want to shutdown the system at 6 PM in the afternoon, you can use it in the following manner: ```shell sudo shutdown 18:00 ``` Cancel a shutdown ```shell sudo shutdown -c ``` Reboot a system ```shell sudo shutdown -r ``` ```shell sudo reboot ``` 		`$ sudo shutdownShutdown scheduled for Thu 2023-03-02 20:12:13 EST, use 'shutdown -c' to cancel.`
###