How to Kill a SSH User Shell Session

As Administrator, when you do a notice that you will some of your users have idle and active ssh session. The idle ssh session could be be due to the hanged ssh session. So the question is how to remove the individual session without killing the active and genuine session.

First thing first, do
#  w
You may get some information like this
18:00:35 up 143 days, 19:57,  3 user,  load average: 0.03, 0.01, 0.05
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT 
user1   pts/31   :24.0            08Oct11 22days  0.05s  0.05s -bash
user2   pts/24   :30              02Jan11  2days  0.66s  0.66s -bash
user3   pts/55   :17              12Nov10 59days  0.01s  0.01s -bash
To get process id (PID) of the idle session, do the command 
#  ps -aux | grep 'pts/31'
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.7/FAQ
root     33541  0.0  0.0  61172   776 pts/1    S+   00:41   0:00 grep pts/31
523      33678  0.0  0.0  64188  1516 pts/31   Ss+   2012   0:00 -bash
Kill the Process
#  kill -9 33678
The idle ssh session has been removed. You can verify with the command "w"