Background and nohup

Surviving the terminal close

A normal background job (./script &) dies when its parent shell exits, because the shell sends SIGHUP. Three ways to keep the job alive after you close the terminal:

• nohup ./script & — start with no-hangup. SIGHUP is ignored. Output goes to nohup.out in the current dir.
• ./script & disown — start, then detach the most recent job from the shell's job table.
• setsid ./script & — start in a new session (decoupled from the controlling terminal entirely).

Don't forget the streams

If the script still writes to the original stdout/stderr (a pipe to the terminal), it'll get SIGPIPE when that terminal closes. Always redirect:

nohup ./script > out.log 2>&1 &

The right tool for long-running stuff

For things you'll come back to: tmux new -s build './script.sh' + tmux attach -t build later. The session keeps a pseudo-terminal alive even when nobody's looking.

For real services: macOS launchd or Linux systemd unit files. The Pippa stack uses launchd to keep pippa serve alive.

Check if a backgrounded job is alive

kill -0 PID && echo alive
ps -p PID

kill -0 sends signal 0, which is "check if you can" rather than "actually do it." Returns 0 if the process exists.