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dracut.asc: document shutdown procedure

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Harald Hoyer 2013-01-18 10:13:14 +01:00
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@ -120,6 +120,26 @@ final cleanup tasks. On an initramfs, the initial root file system cannot be
rotated away. Instead, it is simply emptied and the final root file system
mounted over the top.

== Dracut on shutdown

On a systemd driven system, the dracut initramfs is also used for the shutdown procedure.

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.

= User Manual

== Creating an initramfs Image