BTRFS restoring snapshot disaster

regulator · 2022-02-16 10:50:34

Hi guys, I was not sure what section to put this in..

The latest glibc update broke Dota2 and plasma wayland on my system so I chose to revert to the last snapshot which timeshift takes just before pacman updates something

To be honest I have never restored a snapshot because I was worried something like this would happen..

Basically I restored a snapshot from a few hours ago, with a previous kernel version, but what timeshift does not do(?) is roll back the boot partition to a previous intramfs, so when booting i was presented with "unable to load kernel modules"

I was comfortable enough booting to the ISO, chrooting in and "mkinitcpio --kernel 5.16.8-arch1-1" but this did not fix the issue.

In the end I realised the newer kernel is probably ok and updated it back to the newer 5.16.9 version by chrooting again and pacman --root.

Then I was able to boot again and my system was back to normal

for detective work, I have a disk 3 partitions, happy to provide other info
-main which is BTRFS and LUKS encrypted
-boot ext4 which unlocks the LUKS partition
-efi, fat32 which I understand is required for UEFI boot

further reading, 2 other guys who had the same problem, one uses snapper:
https://forum.manjaro.org/t/emergency-m … y/81890/16

My open question is how do we make restoring snapshots simpler and prevent these issues?

Last edited by regulator (2022-02-16 10:55:21)

V1del · 2022-02-16 11:27:39

You should be more interested in why glibc broke these things. It definitely didn't break Plasma here and I don't have dota installed but could check but it generally shouldn't, did you use an non-standard glibc setup due to the cve/outdated toolchain fear mongering happening?

Since your boot partition is not a btrfs file system there's not much to be done about this (outside of doing custom hoops like rsync "snapshotting" the ext4 partition and then write manual logic that somehow aligns with the btrfs snapshot, which all sounds like more trouble than it's worth), why are you not making the boot partition btrfs as well if you want it to be handled by the snapshot logic? There's little that should prevent you from doing this and there's a grub-btrfs extension that makes GRUB properly understand snapshots (which I doubt would be necessary in this case since the rollback would likely just affect the default snapshot, which normal GRUB should be able to handle on its own).

Last edited by V1del (2022-02-16 11:41:15)

regulator · 2022-02-16 11:41:03

Thanks for the reply, I'm not 100% that glibc created the issues its just a prime suspect, there was also point release kernel, mesa, plasma which could have done it. I suspect glibc because CSGO had a similar issue with some shared libraries. I think Valve are going to tell me I need to use the flatpak version of steam..

I did not know a system is smart enough to read a btrfs partition at boot and two arch BTRFS guides I read both had the boot partition as ext4.. Sounds like I need to switch the boot partition to btrfs and make sure its included in the snapshots, then warn the authors of these install guides..

V1del · 2022-02-16 11:46:38

There's a reason we do not support random install guides, they are written with outdated assumptions, written by people that don't actually have a clue about what they are doing, written by people that don't really understand the available options or which options there are (which is a primary reason why the wiki is written in the style that it is, to present all options in a non opinionated way so that the informed user can make their own decisions on what they are doing) or in most cases all of the above.

ratcheer · 2022-02-16 14:05:55

As to the original question, if you have a separate /boot partition from the btrfs partition you restored, of course it was not restored - it is not included with the snapshot. You are responsible to know it is separate and restore it, additionally.

regulator · 2022-02-16 22:45:33

V1del wrote:

which is a primary reason why the wiki is written in the style that it is, to present all options in a non opinionated way so that the informed user can make their own decisions on what they are doing) or in most cases all of the above.

Yes, I agree.. I noticed tons of guides which don't even bother with disk encryption. I might play around with the guided installer in a VM to see if it can set things up correctly.

ratcheer wrote:

As to the original question, if you have a separate /boot partition from the btrfs partition you restored, of course it was not restored - it is not included with the snapshot. You are responsible to know it is separate and restore it, additionally.

It doesn't make sense to me that kernel&modules are on /boot then there's also essential kernel files or dependencies on / and everything needs to match.. learned something new at least.

I am also reading that you cant convert a boot partition to btrfs, I believe older snapshots will work provided the kernel has not changed? I could keep a 2nd kernel on a fixed version to cater for these circumstances until I feel the need to reformat

Arch Linux

#1 2022-02-16 10:50:34

BTRFS restoring snapshot disaster

#2 2022-02-16 11:27:39

Re: BTRFS restoring snapshot disaster

#3 2022-02-16 11:41:03

Re: BTRFS restoring snapshot disaster

#4 2022-02-16 11:46:38

Re: BTRFS restoring snapshot disaster

#5 2022-02-16 14:05:55

Re: BTRFS restoring snapshot disaster

#6 2022-02-16 22:45:33

Re: BTRFS restoring snapshot disaster

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