It's not always possible to clear all users and you may not personally have the permissions that you need to do so. In that case, stop the server which will kill the connection... eventually. In most cases.
I've had to do that many times for various and sundry reasons. Once the server is down, start checking to see what state any remaining busy sockets are in:
Ideally, this will produce an empty list. In case it doesn't, you'll see sockets in states like FIN_WAIT1, FIN_WAIT2, LAST_ACK (etc), with the first two being the most typical. Access to an Admin or root privledges can help speed up the process, but on my H-PUX box they usually free themselves, drain out in 5 to 15 minutes. I've only had one time where I needed help from an SA to free one last socket that seemed like it was going to hang on forever, hung with a status I hadn't seen before and don't recall.
Once I've seen the sockets, I usually switch to a short version that just shows the count involved, waiting for it to go to zero:
Don't even think about restarting if this doesn't return zero - the engine will come up but the
dsrpcd listener will 'bind bomb' and not be able to start. Meaning, you will not be able to connect from any of your client installations. You can grep for it as a final check of successful engine start. If you do this and it is not running, just stop it again and wait longer. If people get impatient, see if an SA or other Root Wielder can help.