LVM Root Snapshot Rollback on CentOS: Where the Recovery Boundary Ends

The recovery boundary of an LVM root snapshot ends strictly at the logical volume (LV) boundary.

Because CentOS installations typically place /boot on a separate non-LVM partition, a snapshot of the root LV does not revert the state of the boot environment. This creates a critical gap during a failed dnf upgrade rollback: the userspace is restored to a previous state, but the bootloader and kernel files remain in the upgraded state.

Kernel and Userspace Synchronization

When a dnf upgrade installs a new kernel and initramfs, these files are written to /boot. If you roll back the root LV, you restore older binaries and libraries, but /boot still contains the newer kernel. If the system boots into the newer kernel, it will likely fail to load modules because the directory /lib/modules/$(uname -r) in the restored root LV will not match the running kernel version.

Recommendation: You must return the default boot entry to the pre-upgrade kernel version before or immediately after the root LV rollback to ensure the kernel matches the restored userspace.

Thick vs. Thin Snapshot Recovery

The recovery path depends on the LVM snapshot type:

• Thick Snapshots: Recovery requires an in-place merge using lvconvert --merge. This process copies changed blocks back to the origin and can be time-consuming depending on the volume of changes.
• Thin Snapshots: To keep downtime bounded, activating the snapshot as the new origin (promotion) is preferable to a merge. This is nearly instantaneous, though it requires sufficient metadata space in the thin pool.

Excluded Components

The following elements are outside the recovery boundary and will not be reverted:

• EFI System Partition (ESP): Firmware boot entries and UEFI variables are untouched.
• Separate LVs: If /var, /home, or database volumes are on separate LVs, their state persists.
• Post-Snapshot State: Any configuration management runs or database transactions occurring after the snapshot was taken survive the rollback, which may cause application-level inconsistencies.

Diagnostic Requirement: To provide a more specific recovery sequence, please confirm if /boot is on a separate partition or integrated into the LVM volume group.