Can someone tell me how to remove dormant X sessions. This question is similar to Logging out other users from the command line, but more specific to controlling X displays which I find hard to kill.

I used the command "who -u" to get the session of the other screens:

$ who -u

Which gave me:

user1   :0           2014-08-18 12:08   ?          2891 (:0)
user1   pts/26       2014-08-18 16:11 17:18        3984 (:0)
user2   :1           2014-08-18 18:21   ?         25745 (:1)
user1   pts/27       2014-08-18 23:10 00:27        3984 (:0)
user1   pts/32       2014-08-18 23:10 10:42        3984 (:0)
user1   pts/46       2014-08-18 23:14 00:04        3984 (:0)
user1   pts/48       2014-08-19 04:10   .          3984 (:0)

The kill -9 25745 doesn't appear to do anything.

I have a workshop where a number of users will use the computer under their own login. After the workshop is over there are a number of logins that are left open. I would prefer to kill the open sessions rather than try to log into each users' screen.

Again, this question isn't just about logging users' out. I'm hoping to get clarity also for killing/removing stuck processes that are hard to kill.

New Info

While still pondering how to kill the process I wrote the following script, which did it:

#!/bin/bash

results=1   
while [[ $results > 0 ]]
do
    sudo kill -9 25745
    results=$?
    echo -ne "Response:$results..."
    sleep 20
done

After a graceful waiting period, if there isn't a better answer I'll mark this as answered with this resolution. This may resolve the problem with other stuck processes I have had in the past.