nohup

Overview

nohup runs a command immune to SIGHUP, so it keeps running after logout when started from a terminal. Output defaults to nohup.out if not redirected.

Syntax

nohup command [args...]
nohup command [args...] >file 2>&1 &

When to use what

Need	Prefer
Quick one-off after SSH logout	nohup … & or tmux/screen
Survives reboot	systemd user/system service or timer
Managed restart/logs	systemd-run / unit file
Interactive detach	tmux / screen

Examples with Explanations

Classic background job

nohup ./long-job.sh > long-job.log 2>&1 &
echo $!

Default nohup.out

nohup python train.py &
# writes ./nohup.out

Check later

tail -f long-job.log
ps -p <pid> -o pid,etime,cmd

Better: transient systemd unit

systemd-run --unit=longjob --user ./long-job.sh
journalctl --user -u longjob -f

Better: tmux session

tmux new -d -s train './long-job.sh'
tmux attach -t train

Notes

• nohup does not daemonize fully; still a child process.
  
• & backgrounds in the shell; nohup alone still attaches until backgrounded.
  
• disown is a bash alternative after starting a job.

Related Commands

• tmux / screen
  
• systemd-run / systemctl
  
• setsid
  
• timeout — bound runtime