Diagnosing and Fixing openSUSE Btrfs Snapshot Rollback Failures

The Problem: Rollbacks That Don't Stick

In openSUSE Leap (15.5+) and Tumbleweed, the combination of Btrfs, Snapper, and the grub2-snapper-plugin is designed to make system recovery seamless. However, administrators often encounter a specific failure: the snapper rollback command reports success, but the system reboots into the same broken state, or the GRUB boot menu fails to load snapshots with a "file not found" error.

The primary takeaway is that a successful Snapper rollback requires three things to align: the Btrfs default subvolume must be updated, the GRUB configuration must recognize the snapshot path, and the kernel/initrd must exist within that specific snapshot's view of /boot.

Quick Diagnostic Matrix

Symptom	Likely Cause	Diagnostic Command
GRUB snapshot entries missing	Plugin failed to regenerate config	ls /boot/grub2/snapshot/
'File not found' on kernel/initrd	Subvolume path mismatch	btrfs subvolume list / | grep snap
Rollback succeeds but no effect	Booted from wrong subvolume	findmnt /
Snapper timeline is empty	Config disabled or cleanup ran	snapper -c root get-config

Step-by-Step Verification Process

Run these checks in order to isolate whether the failure is at the filesystem level, the bootloader level, or the configuration level.

1. Verify Current Root: Check which subvolume is currently mounted as root.

   # Run as root
   findmnt -n -o SOURCE /

   If the output does not point to a .snapshots path after a rollback, the bootloader is ignoring the Btrfs default subvolume.
2. Audit Available Snapshots: Ensure the snapshot you are attempting to roll back to actually exists and contains data.

   # Run as root
   snapper -c root list

3. Test GRUB Menu Generation: Verify if the grub2-snapper-plugin is actually writing entries to the config.

   # Run as root
   grub2-mkconfig -o /tmp/grub.cfg && grep -c 'snapshot' /tmp/grub.cfg

   If the count is 0, the plugin is not detecting your snapshots.
4. Check Snapper Configuration: Ensure the timeline is active so snapshots are created automatically.

   # Run as root
   snapper -c root get-config | grep -E 'TIMELINE|NUMBER'

Fixes Based on Findings

Scenario A: GRUB Entries are Missing

If the grub2-snapper-plugin is inactive, the boot menu won't show your snapshots. Restart the service and force a config update.

# Run as root
systemctl restart grub2-snapper-plugin.service
grub2-mkconfig -o /boot/grub2/grub.cfg

Scenario B: Rollback Reports Success but System Doesn't Change

This usually happens when the system is booting via a hardcoded subvolume ID rather than the Btrfs "default". You can manually force the default subvolume to the desired snapshot.

# Run as root
# Identify the snapshot ID from 'snapper list', then:
btrfs subvolume set-default $(btrfs subvolume list / | grep '@/.snapshots/[0-9]*/snapshot' | head -1 | awk '{print $2}') /

Risk: Manual set-default bypasses Snapper's internal tracking. Future snapper rollback commands may behave unexpectedly until a new snapshot is created and set as default.

Scenario C: Timeline is Empty

If no snapshots are being created, enable the timeline feature.

# Run as root
snapper -c root set-config TIMELINE_CREATE=yes

Verification of Fix

To confirm the system is now recoverable:

• Reboot and select a snapshot from the Advanced options for openSUSE menu in GRUB.
• Once booted, run findmnt /. The source should explicitly include the .snapshots/X/snapshot path.
• Run snapper -c root list to confirm a new pre/post snapshot pair was created for the rollback operation.

When to Escalate

If the above steps fail, the issue may be deeper than a configuration error. Escalate to openSUSE Bugzilla or senior engineering if:

• The grub2-snapper-plugin service fails with permission errors on /boot/grub2.
• btrfs check --readonly /dev/root reports filesystem corruption. (Warning: Never run btrfs check on a mounted filesystem).
• The kernel or initrd is missing from /boot after a zypper dup, requiring a manual dracut -f and grub2-mkconfig.

Limitations

This guide applies to traditional openSUSE Leap and Tumbleweed installations. It does not apply to MicroOS or Aeon, which use a read-only root filesystem and a different transactional update mechanism. Additionally, if you have a separate /boot partition (not on Btrfs), the grub2-snapper-plugin cannot snapshot the kernel, and snapshot boot entries will fail.