Could not mount Btrfs subvolume '/@/snapshots'

Direct Answer

The system does not guarantee a bootable state if ROLLBACK_ON_TRANSACTION_FAILURE is disabled (the Leap 15.5 default) and the transaction corrupted critical files. The pre-transaction snapshot remains intact as a read-only Btrfs snapshot, but the active root subvolume may be left in a broken state.

The definitive recovery mechanism: boot from the pre-failure snapshot via GRUB's "Start bootloader from a read-only snapshot" menu entry (created by grub2-snapper during the transaction), then run snapper rollback from that booted snapshot to make it the new default subvolume.

Verifying Pre-Failure State Integrity

Mount the read-only snapshot subvolume and run rpm -V against it—this verifies package integrity without log parsing.

# Identify the pre-transaction snapshot number
btrfs subvolume list / | grep snapshots

# Mount read-only (replace X with snapshot number)
mount -o ro,subvol=@/.snapshots/X/snapshot /mnt

# Verify all packages
rpm -Va --root=/mnt

A clean rpm -Va output (no missing files, no checksum mismatches) confirms the snapshot is a viable recovery point.

Why the Mount Fails

The error Could not mount Btrfs subvolume '/@/snapshots' typically means the @/.snapshots subvolume exists on disk but is not mounted at /.snapshots. In the installer's chroot environment this mount is often missing; on a booted system it requires an /etc/fstab entry:

UUID=...  /.snapshots  btrfs  subvol=@/.snapshots  0  0

Permissions on /.snapshots must be 750 root:snapper.

Critical Assumptions & Uncertainties

• Assumes Leap 15.5 with snapper 0.8.x; Tumbleweed (0.10+) behaves differently.
• GRUB snapshot menu entries only exist if grub2-snapper ran successfully during the transaction. Early transaction failures may lack entries.
• If Btrfs metadata itself is corrupted, snapshots may be unreadable regardless of mount status.
• The error may stem from the installer's chroot lacking the /.snapshots mount, not the target system. Distinguish installation-time vs. booted-system context.

One Diagnostic Detail Needed

Are you seeing this error during installation (in the installer chroot) or on a booted system after a failed update? The recovery path differs: the installer environment has no GRUB snapshot menu, so you must manually mount the target's @/.snapshots subvolume and run snapper rollback from a rescue shell.