dracut-shutdown.service(8) unpack the initramfs to /run/initramfs




This service unpacks the initramfs image to /run/initramfs. systemd pivots into /run/initramfs at shutdown, so the root filesytem can be safely unmounted.

The following steps are executed during a shutdown:

• systemd switches to the shutdown.target

• systemd starts /lib/systemd/system/shutdown.target.wants/dracut-shutdown.service

• dracut-shutdown.service executes /usr/lib/dracut/dracut-initramfs-restore which unpacks the initramfs to /run/initramfs

• systemd finishes shutdown.target

• systemd kills all processes

• systemd tries to unmount everything and mounts the remaining read-only

• systemd checks, if there is a /run/initramfs/shutdown executable

• if yes, it does a pivot_root to /run/initramfs and executes ./shutdown. The old root is then mounted on /oldroot. /usr/lib/dracut/modules.d/99shutdown/shutdown.sh is the shutdown executable.

• shutdown will try to umount every /oldroot mount and calls the various shutdown hooks from the dracut modules

This ensures, that all devices are disassembled and unmounted cleanly.

To debug the shutdown process, you can get a shell in the shutdown procedure by injecting "rd.break=pre-shutdown rd.shell" or "rd.break=shutdown rd.shell".

# mkdir -p /run/initramfs/etc/cmdline.d
# echo "rd.break=pre-shutdown rd.shell" > /run/initramfs/etc/cmdline.d/debug.conf
# touch /run/initramfs/.need_shutdown


Harald Hoyer