or you can
Code:
ps aux | grep ssh
pkill [processnumber]
where [processnumber] is the number of the ssh process that the user is using to log into your system.
And if you want to keep a specific user out, as root you can run
Code:
passwd -l [username]
And then they cannot sign back in, because their password is locked. Unlock it with
Code:
passwd -u [username]
logically.
Ian