Add a finalrd script to move filesystems #124
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`/mnt/run/base` contains the snap file that is mounted on `/`. For that reason it is not possible to unmount `/mnt/run/base` until we have switched root to the shutdown ramfs. At this point before we move `/sysroot/mnt/run/base` out of `/sysroot` so that `systemd-shutdown` is able to unmount all filesystems. `systemd-shutdown` allows hooks. But they are called right after `systemd-shutdown`. That means we cannot run a hook after the root switch and before `systemd-shutdown`. For that reason the finalrd hook replaces `systemd-shutdown` in the ramfs by a wrapper. This solution is not elegant. In the long term we should try to make `systemd-shutdown` always move all sub mount points before trying to unmount. Also, there is still an error message when systemd tries to umount `/mnt/run/base` before switching root. There does not seem to be anyway to make `mnt-run-base.mount` perpetual.
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Note there also snapcore/snapd#11119 to at least help |
| # systemd-shutdown has hooks, but they are run either before | ||
| # switch, or after unmounts. | ||
| # It would be better to make systemd-shutdown smarter and move | ||
| # all found mounts before trying to unmount them. |
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somehow i would rather try to fix this in systemd-shutdown itself, instead of adding all of this into core20. Given that systemd-shutdown is C and can execute all of these things.
or for example, if some else can be done as a finalrd hook easier.
For example, can we have finalrd/core.finalrd hook that simply does umount --lazy /run/mnt/* ?
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Yes, I will try to change systemd-shutdown to move filesystems in sub mount points. It should be an acceptable improvement for upstream.
The issue with --lazy is that it does not give you an error if it does not manage to unmount before shutdown. At least I am not aware of any way to check the active detached mounts. If only we had that, we could just mark run-mnt-base.mount as LazyUmount=yes, and verify it was really unmounted in a system-shutdown hook after systemd-shutdown has umounted /sysroot.
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We fixed it in systemd in systemd/systemd#25168 . So it will be fixed in uc24. And along this there is snapcore/core-base#93 and snapcore/core-base#83 which we could backport. On snapd side there was also snapcore/snapd#11119 |
/mnt/run/basecontains the snap file that is mounted on/. Forthat reason it is not possible to unmount
/mnt/run/baseuntil wehave switched root to the shutdown ramfs.
At this point before we move
/sysroot/mnt/run/baseout of/sysrootso that
systemd-shutdownis able to unmount all filesystems.systemd-shutdownallows hooks. But they are called right aftersystemd-shutdown. That means we cannot run a hook after the rootswitch and before
systemd-shutdown. For that reason thefinalrd hook replaces
systemd-shutdownin the ramfs by a wrapper.This solution is not elegant. In the long term we should try to make
systemd-shutdownalways move all sub mount points before trying tounmount.
Also, there is still an error message when systemd tries to umount
/mnt/run/basebefore switching root. There does not seem to beanyway to make
mnt-run-base.mountperpetual.