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 form that can be easily comprehended by a new user. `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]

~~columns for~~ `ps -f` `UID PID PPID C STIME TTY TIME CMD` ~~columns for~~ `ps u` `USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND`	`ps ps -ef ps -aux`
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.`
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:* LISTEN 0 4096 0.0.0.0:8081 0.0.0.0:* LISTEN 0 4096 0.0.0.0:8082 0.0.0.0:` `$ ss -a '( dport = :80 or sport = :80 )' Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port ProcessPortProcess 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.
Syntax: shutdown

shutdown

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