Cannot create Timeshift Backup on BTRFS: system disk with root subvolume (@)

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So I’m on Fedora 34 with the BTRFS and when I try to create a system backup on my btrfs partition with timeshift, I get error "Selected snapshot device is not a system disk
Select a BTRFS system disk with root subvolume (@) "

I’ve done some duckducking on the issue and I saw on reddit that it had something to do with fstab using the old / root. Apparently it’s fixable by booting onto a live pen and making a snapshot and so on… I’m just not advanced enough to understand the procedures that were given.

Any easier fix out there?

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Could you post the link, to see what exactly you mean.

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Here it is
https://www.reddit.com/r/btrfs/comments/jx71fp/getting_error_select_btrfs_system_disk_with_root/

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Another thread:

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Instead of changing the subvolume’s name in the installer, I recommend changing it post-install. There’s a bug if you rename the / subvolume (it’s not a bad bug but …)

https://bugzilla.redhat.com/show_bug.cgi?id=1952764

You need to identify which /dev/ node and partition has the btrfs filesystem used for / and /home and mount its top-level so you can rename the subvolumes:

lsblk -f
mount /dev/sdXY /mnt
cd /mnt
mv root @
mv home @home
nano /etc/fstab

In nano:

  • Change subvol=root to subvol=@ for the / mount point.
  • Change subvol=home to subvol=@home for the /home mount point.

Next change each /boot/loader/entries/*conf file’s rootflags=subvol=root to rootlfags=subvol=@ I think it’s easier to just use nano to it in this case, one by one; OR…

It is possible to use grubby to change the BLS drop-in files in /boot/loader/entries instead, which is ordinarily the preferred way, but in this case it involves some extra steps than just using nano or vim.

grubby --remove-arg="rootflags=subvol=root" --update-kernel=ALL
grubby --arg="rootflags=subvol=@" --update-kernel=ALL
nano /etc/default/grub

Remove rootflags=subvol=@ from the /etc/default/grub file - it’s here because of the update-kernel=ALL flag above, but grub has its own way of adding it.

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Thank you for your solution Chris I really appreciate it. However I won’t even dare trying these since it’s a bit much for me and I’m scared I will break the system.

It’s a bit of a shame there is not a user-friendlier solution, I don’t think anyone should have to go through those after a fresh install.

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Just my opinion but the real issue here is a limitation of timeshift. It requires a highly specific layout for btrfs subvolumes for it to work properly. There is no real valid reason why the root subvolume should be mounted as @. It isn’t even a widely used convention outside of Ubuntu.

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Hello, there. I know it has been a while, but I tried this yesterday and it seems to work perfectly (thank you so much!), but one question remains. At a certain point, grubby modifies the /boot/loader/entries/ files of all available kernels. Assuming I followed all the process and chose to use grubby when the option was presented, are the changes I made gonna persist when a new kernel is installed? Thanks again in advance.

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It does persist across kernel installs.

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Timeshift does have trouble restoring sometimes. I couldn’t get my system to restore two times and I lost a lot of data.

I am trying to work on a way to have a recovery partion with Fedora. Even though btrfs has snapshots they are not so straightforward for users who dont know the syntax’s.

A recovery partition implemented quite well I have seen on PopOS & MacOS. It would be incredible for Fedora, also Nvidia driver options at install.

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