Let's see my case for an instance, first of all, list all the online users now.
[root@localhost ~]# w
22:17:51 up 98 days, 18:19, 2 users, load average: 0.00, 0.05, 0.06
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root pts/1 192.168.10.123 22:02 0.00s 0.05s 0.00s w
steven tty5 - 22:17 4.00s 0.00s 0.00s -bash
There's a user steven which console was terminated abnormally and it's no longer used. We were trying to remove the unused session from the system.
Let's see what processes relate to steven.
[root@localhost ~]# ps -ef | grep steven
root 20930 1 0 22:16 ? 00:00:00 login -- steven
steven 20934 20930 0 22:17 tty5 00:00:00 -bash
...
Found a root process named login -- steven which initiated the session. So let's kill the root process 20930 on the first line.
[root@localhost ~]# kill -9 20930
The user steven was gone.
[root@localhost ~]# w
22:18:57 up 51 days, 18:20, 1 user, load average: 0.00, 0.03, 0.05
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root pts/1 192.168.10.123 22:02 0.00s 0.05s 0.00s w
[root@localhost ~]# ps -ef | grep steven
...