How to run a command BEFORE shutdown on Ubuntu 21.04

I just want to run (as root) a command or script before each reboot/shutdown/poweroff on Ubuntu 21.04 (when I run the shutdown or poweroff commands, or using GNOME/KDE GUI options). I've tried putting the script inside /etc/init.d and making symlinks to /etc/rc6.d/ and /etc/rc0.d/ but doesn't work.

Wonder if there's such a line for sudo crontab -e.

1 Answer

You can do this by creating a service file, then reloading systemd. Here's how:

0. Open Terminal (if it's not already open)

1. Ensure the script that you want to run at shutdown is executable:

   chmod +x ~/scripts/pre-shutdown.sh

2. Create a file in /etc/systemd/system for the shutdown service. For the sake of this example, I'll call my file nighty-night.service.

3. Add the following lines to the .service file, modifying it as needed:

   [Unit]
   Description=Pre-Shutdown Processes
   DefaultDependencies=no
   Before=shutdown.target reboot.target halt.target
   # This works because it is installed in the target and will be
   # executed before the target state is entered
   # Also consider kexec.target
   [Service]
   Type=oneshot
   User=smeterlink
   Group= smeterlink
   ExecStart=/home/smeterlink/scripts/pre-shutdown.sh # your path and filename
   [Install]
   WantedBy=halt.target reboot.target shutdown.target

4. Restart the daemon:

   sudo systemctl daemon-reload

That's all there is to it.

4

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