If you’re using HPC, chances are that your University/Sysadmin has a policy about how long you can stay inactive with the established SSH connection. If you are frustrated with this automatic disconnections, here is a way to prevent this. You can either:
ssh -o "ServerAliveInterval 60" -X email@example.com
or create a file in ~/.ssh/config with the following line:
This will enable ssh client keepalives. The above line will send an ssh keepalive every 60 seconds that will prevent network devices from considering the session as idle.