Does this tool support online rollback?

[developer91234]

Not clear from the documentation and I don't have an arch btrfs system to test. Would you be able to rollback the mounted root subvolume in place? Also, if I were booted into a snapshot, the rollback script would rollback the root subvolume, correct?

[hirak99]

Yes, online rollback is supported.

The yabsnap rollback-gen ID command generates a short bash script.

You will need to review the script and run it manually (or type in the commands one by one).

It can be run from the system mounted on the root which you want to roll back. After you run the script, the system will continue to function with the current snapshot until you reboot, upon which the rollback will take effect.

For rollback to work correctly, root should be mounted (in fstab) with subvol= and not subvolid=.

[hirak99]

Also fyi, here's an example of rollback script it generates. This should clarify exactly how the rollback process works.

Command -

$ yabsnap rollback-gen 20240728183030

Output -

#!/bin/bash
# Save this to a script, review and run as root to perform the rollback.

set -uexo pipefail

mkdir -p /run/mount/_yabsnap_internal_0
mount /dev/mapper/luksdev /run/mount/_yabsnap_internal_0 -o subvolid=5

cd /run/mount/_yabsnap_internal_0

mv @home @.snapshots/rollback_20240728192848_@home
btrfs subvolume snapshot /.snapshots/@home-20240728183030 @home

mv @ @.snapshots/rollback_20240728192848_@
btrfs subvolume snapshot /.snapshots/@root-20240728183030 @

echo Please reboot to complete the rollback.
echo
echo After reboot you may delete -
echo "# sudo btrfs subvolume delete /.snapshots/rollback_20240728192848_@home"
echo "# sudo btrfs subvolume delete /.snapshots/rollback_20240728192848_@"

[developer91234]

Thanks. Please consider letting the user do rollbacks without saving the script as this is quite cumbersome. After all the operation is reversible, maybe just inform the user of the changes after they're done and allow them to undo it if they want.

[hirak99]

Perhaps we should add a --run option to rollback-gen. Might as well alias that to a new command, rollback.

It can print the script, confirm with the user, then run it.

Initial reason for not doing this was safety, but I think the code has matured enough (and tested enough times) for this to makes sense.

Optionally, --noconfirm can also be added, although that is probably veering a bit too far into the "dangerous" territory.

[hirak99]

The rollback command (with optional --noconfirm) is implemented and released as v2.2.2. Along with displaying the script for review, this will also execute it after an interactive confirmation.

Thanks to @Tql-ws1 for help with this and more!