Description

One of the various commands we mentioned was the who command which displays users who are currently logged on to a Linux system, including the terminals they are connecting from.

This article will explain some useful examples of who command in Linux .

The basic syntax for using who command is as follows.

# who who [OPTION]... [ FILE | ARG1 ARG2 ]

1. If you run who command without any arguments, it will display account information (user login name, user’s terminal, time of login as well as the host the user is logged in from) on your system similar to the one shown in the following output.

[root@vps ~]# who
root pts/0 2018-07-23 01:04 (123.14.15.26)

2. To print the heading of the columns displayed, use the -H flag as shown.

[root@vps ~]# who -H
NAME LINE TIME COMMENT
root pts/0 2018-07-23 01:04 (123.14.15.26)

3. To print the login names and total number of logged on users, use the -q flag.

[root@vps ~]# who -q
root
# users=1

4. In case you want to show only hostname and user associated with stdin, use the –m switch.

[root@vps ~]# who -m
root pts/0 2018-07-23 01:04 (123.14.15.26)

5. Next, to add user’s message status as +, – or ?, use the -T option.

[root@vps ~]# who -T
root + pts/0 2018-07-23 01:04 (123.14.15.26)

The who command also helps you to view some useful system information such as last boot time, current runlevel (target under systemd), print dead processes as well as processes spawned by init.

6. To view the time of last system boot, use the -b flag and adding the -u option allows for listing of logged on users in the same output.

[root@vps ~]# who -b
system boot 2018-07-23 12:54

7. You can check the current runlevel with the -r option.

[root@vps ~]# who -r
run-level 3 2018-07-23 12:55

8. The following command will print dead processes.

[root@vps ~]# who -d
pts/1 2018-07-23 11:10 9986 id=ts/1 term=0 exit=

9. Furthermore, to see active processes spawned by init, use the -p option.

[root@vps ~]# who -p

10. The -a flag allows for printing of default output combined with information from some of the options we have covered.

[root@vps ~]# who -a
system boot 2018-07-23 12:54
LOGIN hvc0 2018-07-23 12:55 709 id=hvc0
LOGIN tty1 2018-07-23 12:55 711 id=tty1
run-level 3 2018-07-23 12:55
root + pts/0 2018-07-23 01:04 . 6861 (123.14.15.26)

We hope you’ve found this useful!