`tmux` to support long running terminal sessions¶

When you connect to the cluster via SSH, your session is tied to that connection — if it drops, any running processes are lost. tmux (terminal multiplexer) solves this by running a persistent session on the login node that survives disconnections. It also lets you split your terminal into multiple panes and windows within a single SSH connection.

Note

The figure above gives an overview of how tmux sits between your SSH client and your shell processes on the login node.

Managing sessions¶

Open a new session¶

Always give your session a descriptive name so you can identify it later:

tmux new -s mysession

Detach from a session¶

Detaching leaves the session (and anything running inside it) alive on the server. You can safely close your terminal after detaching.

Action	Keybind
Detach from current session	`Ctrl`+`B` then `d`

List your sessions¶

tmux ls

Attach to an existing session¶

tmux attach -t mysession

If you only have one session running, tmux attach alone is sufficient.

Kill a session¶

When you are done and no longer need the session:

tmux kill-session -t mysession

Scrolling¶

By default, the scroll wheel does not work inside tmux. You need to enter copy mode first:

Action	Keybind
Enter copy mode	`Ctrl`+`B` then `[`
Scroll up	`Up` / `Page Up`
Scroll down	`Down` / `Page Down`
Exit copy mode	`q`

Multiplexing — windows and panes¶

tmux lets you split a single session into multiple panes (splits within one view) and windows (separate tabs).

Panes¶

Action	Keybind
Split horizontally (top/bottom)	`Ctrl`+`B` then `"`
Split vertically (left/right)	`Ctrl`+`B` then `%`
Close current pane	`Ctrl`+`B` then `x`

Windows¶

Action	Keybind
New window	`Ctrl`+`B` then `c`
Next window	`Ctrl`+`B` then `n`
Previous window	`Ctrl`+`B` then `p`
Switch to window by number	`Ctrl`+`B` then `0`–`9`
Close current window	`Ctrl`+`B` then `&`

Navigating between panes¶

Action	Keybind
Move to pane (arrow keys)	`Ctrl`+`B` then `Up` / `Down` / `Left` / `Right`
Cycle through panes	`Ctrl`+`B` then `o`

Typical multiplexing workflow

A common pattern on the cluster is to open one pane for an interactive srun job, a second pane to monitor it with squeue or nvidia-smi, and a third for editing scripts — all within a single detachable tmux session.

Troubleshooting¶

"sessions should be nested with care, unset $TMUX to force"¶

This warning appears when you run tmux new -s <name> from inside an existing tmux session

If you're unsure whether you're already inside tmux, check with following command : ( Or check the for green strip on the bottom of the terminal),
```
echo $TMUX
```
Cannot connect to or create any tmux sessions¶

Symptoms: Running tmux attach or tmux new fails with an error similar to:
```
server exited unexpectedly
```
```
error connecting to /tmp/tmux-XXXXX/default (No such file or directory)
```
```
no server running 
```
This is typically caused by a stale or corrupted tmux socket directory in /tmp, often left behind after a node reboot or an unclean disconnection.

Fix:

This will terminate all running tmux sessions

The steps below delete the tmux socket directory, which kills any active or detached sessions and all processes running inside them. Make sure you are not relying on anything currently running in tmux before proceeding.
1. Locate your tmux directory in /tmp. It is named after your numeric user ID:
```
ls /tmp | grep tmux
```
  You should see something like tmux-XXXXX where XXXXX is your UID. Confirm it belongs to you:
```
ls -la /tmp | grep tmux
```
2. Delete it:
```
rm -rf /tmp/tmux-$(id -u)
```
3. Start a fresh session:
```
tmux new -s mysession
```
  A non-empty value means you're in an active session.

tmux to support long running terminal sessions¶