Arch Linux

4romany

Member

Registered: 2021-11-27

Posts: 25

(CLOSED) Failed to mount /boot after doing timeshift restore on BTRFS

So I install the lastest Arch install last week - using BTRFS as my file system.   I used the archinstall and pretty much kept the default.  Everything has worked perfectly.  I install timeshift (using btrfs) - and I was playing around with it - I created a backup - and than ran a full system update - and than I used timeshift to restore the the snapshot I just created.   Reboot - and it fails when attempting to mount /boot (FAILED TO MOUNT BOOT).   So booted up with Arch install ISO - and tried to follow the steps to reverse the timeshift backup.   The nvme0n1 has 2 partition - p1 is what I think is the boot partition (if I understand that name) - 511M FAT32.   p2 should contain all of the root files/directory - its 476G and it BTRFS.  I can mount p2 (mount /dev/nvme0np2 /mnt) and I can see my directories on /mnt.   The arch recovery wiki says to also mount /dev/bootDevice /mnt/boot.  If I try using the p1 partition it says mount point does not exit - same error if I use P2.   If I proceed with using: arch-chroot /mnt I also get a error about mount point does not exist.   Not sure if because I'm using btrfs and subvolume this procedure needs to be adjusted.    Hopefully someone can throw some breadcrumbs I can follow...

....Romany

Last edited by 4romany (2023-03-14 02:35:44)

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 24,970

Re: (CLOSED) Failed to mount /boot after doing timeshift restore on BTRFS

Generally the behaviour here is expected in so far that the /boot partition containing the kernel images is not part of the BTRFS snapshots due to being the ESP FAT partition. So what will happen here is that the BTRFS snapshot you are attempting to boot into will contain old kernel modules that do not match the contents of your /boot partition anymore. You could try booting the fallback image in that case which should contain everything, the more "proper" approach is to downgrade the kernel manually as well.

That for why that breakage happened. As for mounting things properly, to mount BTRFS you will need to add the -o subvol=@ option to mount the root subvolume correctly, see https://wiki.archlinux.org/title/Btrfs# … subvolumes

4romany

Member

Registered: 2021-11-27

Posts: 25

Re: (CLOSED) Failed to mount /boot after doing timeshift restore on BTRFS

I was able to chroot to my disks but made very little progress - just because of my lack of knowledge with btrfs and timeshift via CLI.   So I tried out what was hopefully an easier "point and click" solution - downloaded an ISO of mint - that had timeshift - booted up in live mode - ran the gui of timeshift - it saw all of my snapshots.  I picked an older one - reboot - and still no boot - but not the FAILED TO MOUNT BOOT - this time it could not find /home.  I changed the subvolume ID in my etc/fstab file to another /home snapshot - and that did the trick.   After a sucessful boot I moved what important files I wanted to save to another disk - and re-installed arch - this time with EXT4.  Many thanks to V1del with his quick reply - it gave me a direction to troubleshoot.  I'm surprised that there is not more complaints about this kind of issue with BTRFS and timeshift and restoration - but if they are my searching techniques found very little.  I've used timeshift many time in restoring a previous save - and never had an issue with a EXT4 filesystem.

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 24,970

Re: (CLOSED) Failed to mount /boot after doing timeshift restore on BTRFS

This isn't really the fault of BTRFS or timeshit for that matter. If your kernel image does not get downgraded as well then you can't boot into an old snapshot with the new kernel, you can set things up so that the kernel is snapshotted as well and then use e.g. grub-btrfs to actually boot into a specific snapshot but that would mandate the kernel images are on BTRFS/hence your ESP not mounted to /boot but e.g. /efi or so, but the archinstall script making automated/common denominator choices here will potentially limit you here.