Tutor on a Linux server.
When I shut down the server, are all the Tutor processes shut down automatically (especially MongoDB), or should I first run “tutor local stop”? If I do this, I have to manually run “tutor local start -d” after rebooting.
Is there a way I can find out who is currently active on the server before I shut down, and is it possible to message them?
Yes, they are.
No, you should not.
Exactly 
This is because the restart policy of the containers is set to “unless-stopped”.
It’s certainly possible but it’s complicated. You could check the IDs of active users in the tracking logs (~/.local/share/tutor/data/lms/logs/tracking.log).
Thanks, Regis. I appreciate it a lot. I did a lot of searching before I asked. 
Here’s a super-crude solution that works well enough for me:
tail -10 ~/.local/share/tutor/data/lms/logs/tracking.log | sed -e 's/,.*"username"://' -e 's/,.*//'
Laugh, but enjoy! 