tmux attach, detach, list and kill: the long-job workflow

Start a named session for a long job

When you kick off a long build, backup, migration or training run over SSH, create a named session with tmux new -s train, which puts you straight into it. If you do not want to enter it right away, tmux new -d -s train creates it detached.

You can pass the job directly, as in tmux new -d -s train 'python -u train.py'. That runs the command as the session's only program: when it exits, the window closes and the session disappears, taking the final output with it. To keep the output, start the session with a shell and type the command into it:

# Start a session and attach to it
tmux new -s train

# Or create it detached and type the job into its shell
tmux new -d -s train
tmux send-keys -t train 'python -u train.py' Enter

Detach, log out and come back

Once the job is running inside tmux, press Ctrl-b d (the prefix, then d) to detach. The session and everything in it keeps going on the server after you log out of SSH.

When you log back in, run tmux ls to see what is running. It prints one line per session and adds (attached) at the end when a client is connected to it:

$ tmux ls
train: 1 windows (created Thu Oct 29 23:54:33 2026)
$ tmux attach -t train

tmux a -t train also works, because tmux accepts unambiguous command prefixes. If the session is still attached somewhere else, tmux attach -d -t train detaches every other client first, while tmux attach -r -t train attaches read-only without disturbing anything. For one command that attaches when train exists and creates it otherwise, use tmux new -A -s train.

Kill sessions you no longer need

tmux rename-session -t old new renames a running session. When the job is done and you have read the output, end the session by typing exit in its last shell, or from outside with tmux kill-session -t train.

To clean up leftovers at once, tmux kill-session -a -t train kills every session except train and tmux kill-server ends them all. With no sessions left, tmux prints no server running on /tmp/tmux-1000/default (the number is your user id); a wrong name gives can't find session: NAME.

Every other key binding is in the tmux cheat sheet.

When tmux dies after you log out (systemd)

Sometimes you detach, log out and come back to find the session gone. The usual cause is the systemd-logind setting KillUserProcesses=, whose upstream default is yes. The logind.conf manual itself warns that this breaks tools like screen and tmux unless they are moved out of the session scope.

Many distributions build with no instead. Debian 13, for example, ships #KillUserProcesses=no in /etc/systemd/logind.conf. On a system where it is yes, logging out kills both tmux and your job.

Check the effective value and your lingering status, then start tmux outside your login session, as the systemd-run manual shows:

busctl get-property org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager KillUserProcesses
loginctl show-user $USER -p Linger

# Keep your user manager running after the last logout, then start tmux under it
loginctl enable-linger
systemd-run --scope --user tmux new -s train

In the default configuration you can enable lingering for yourself without root. An admin can also set KillUserProcesses=no in /etc/systemd/logind.conf or list specific users in KillExcludeUsers=. Other ways to keep a job alive are in run a process in the background on Linux.

Check on a job without attaching

You do not have to attach just to see what your job is doing. tmux capture-pane -p -t train prints what is on the pane's screen; add -S -20 to start 20 lines back in the history, or -S - for all of it. For a continuous log file, tmux pipe-pane -o -t train 'cat >> ~/train.log' copies everything the pane prints from now on into ~/train.log, carriage returns included.

# Last 3 non-empty lines of the pane, from a script or a cron job
tmux capture-pane -p -t train | grep -v '^$' | tail -n 3

# Log everything the pane prints from now on
tmux pipe-pane -o -t train 'cat >> ~/train.log'

Both commands still need an SSH session every time you want to look. Also pass environment variables with tmux new -e NAME=value, because a tmux server that is already running does not see variables you export later.