Prolonging terminal sessions

For working on the clusters, most users will need to use SSH to connect to the cluster for job submission and monitoring, editing files and so forth. Keeping this SSH connection alive for a long period of time, ranging from hours to days, may be necessary for some users and this page proposes a variety of techniques for keeping such a terminal session alive.

SSH configuration

One simple solution is to modify the configuration of your SSH client to prolong the connection. On MacOS and Linux the client configuration is found in $HOME/.ssh/config while in Windows it is in C:\Users\<username>\.ssh\config, where you can add the lines

Host *
    ServerAliveInterval 240

which will send a sign-of-life signal over the SSH connection to the cluster every four minutes (240 seconds).

TMUX

tmux is a terminal multiplexer that allows multiple virtual sessions in a single terminal session. You can also disconnect from an SSH server without interrupting its process(es).

Cheat sheet

For a complete reference, see this page.

Command	Description
tmux	Start a server
Ctrl+B D	Disconnect from server
tmux a	Reconnect to server
Ctrl+B C	Create a new window
Ctrl+B N	Go to next window
Ctrl+B [	Enable "copy" mode, allowing to scroll with the mouse and Page-Up Page-Down
Esc	Disable "copy" mode

Launch tmux inside a job submitted through tmux

If you submit a job with tmux and try to start tmux within the same job, you will get the lost server error message. This happens because the $TMUX environment variable pointing to the tmux server is propagated to the job. The value of the variable is not valid and you can reset it with:

[name@server ~]$ unset TMUX

However, nested use of tmux is not recommended. To send commands to a nested tmux, one has to hit Ctrl+B twice; for example, to create a new window, one has to use Ctrl+B Ctrl+B C. Consider using screen inside your job (if you are using tmux on a login node).