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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 rotated away. Instead, it is simply emptied and the final root file system
mounted over the top. 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 = User Manual


== Creating an initramfs Image == Creating an initramfs Image