How to Force Users to Terminate, Exit or Logout

To force an online or dead user to logout, you can use skill to terminate her/his session. For example, I am a root and at terminal pts/2 now:
[root@test ~]# tty
/dev/pts/2
[root@test ~]# w
...
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/2    10.13.32.238     22:01    0.00s  0.04s  0.00s w
steven   pts/3    10.13.40.143     23:21    3.00s  0.01s  0.01s ssh elsa@localhost
elsa     pts/4    localhost        23:21    3.00s  0.00s  0.00s -bash
As you can see, there are 3 users online, but the third connection is sshed and used by the second user "steven".

At this moment, I know "steven" forgot to exit his terminal. So I can skill the idle user now.
[root@test ~]# skill -u steven
[root@test ~]# w
...
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/2    10.13.32.238     22:01    0.00s  0.04s  0.00s w
steven   pts/3    10.13.40.143     23:21   24.00s  0.00s  0.00s -bash
The third connection is terminated, but the user "steven" is still there. This is becuase skill uses TERM by default. Therefore, we should signal KILL explicitly like this:
[root@test ~]# skill -KILL -u steven
[root@test ~]# w
...
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/2    10.13.40.238     22:01    0.00s  0.04s  0.00s w

Now, we have cleaned the all unused connections.