DRACUT-SHUTDOWN.S(8)

NAME
dracut-shutdown.service - unpack the initramfs to /run/initramfs

SYNOPSIS

dracut-shutdown.service

DESCRIPTION

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

The following steps are executed during a shutdown:

    • The system starts to shut down

    • ``$prefix/lib/systemd/system/sysinit.target.wants/dracut-shutdown.service`` gets its ``ExecStop`` target triggered.

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

    • 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/[0-9][0-9]shutdown/shutdown.sh`` is the shutdown executable.

    • shutdown will try to unmount 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/50-debug.conf
    # touch /run/initramfs/.need_shutdown

In case the unpack of the initramfs fails, dracut-shutdown-onfailure.service executes to make sure switch root doesn’t happen, since it would result in switching to an incomplete initramfs.

AUTHORS

Harald Hoyer

SEE ALSO

dracut(8)