What is /usr/lib/systemd/system-shutdown ?

Everyone probably has heard of startup scripts such as Cloud-init or user-data which is passed as a startup script even libvirt has this feature.

Running a shutdown script is however not mentioned much, now why would you need a shutdown script, sometimes, a shutdown script is needed to do various things such as collect diagnosis etc.

The path /usr/lib/systemd/system-shutdown/ runs these scripts, however they are run quite late hence the system is mostly in read-only mode, for example to create a log file one would have to do

cat /usr/lib/systemd/system-shutdown/debug.sh #!/bin/sh mount -o remount,rw / dmesg > /home/leon/shutdown-log mount -o remount,ro / 

The other way is to use a systemd script:

cat /etc/systemd/system/demo.service [Unit] Description=Run my custom task at shutdown only DefaultDependencies=no Conflicts=reboot.target Before=poweroff.target halt.target shutdown.target Requires=poweroff.target [Service] Type=oneshot ExecStart=/tmp/script.sh start RemainAfterExit=yes [Install] WantedBy=shutdown.target 

This example is taken from here.

This is a pretty neat way to run shutdown scripts.