7.7 Frequently Asked Questions

Why does Snapper Never Show Changes in /var/log, /tmp and Other Directories?

For some directories we decided to exclude them from snapshots. See Section 7.1.2, Directories That Are Excluded from Snapshots for a list and reasons. To exclude a path from snapshots we create a subvolume for that path.

How much disk space is used by snapshots? How to free disk space?

Displaying the amount of disk space a snapshot allocates is currently not supported by the Btrfs tools. However, if you have quota enabled, it is possible to determine how much space would be freed if all snapshots would be deleted:

  1. Get the quota group ID (1/0 in the following example):

    tux > sudo snapper -c root get-config | grep QGROUP
    QGROUP                 | 1/0
  2. Rescan the subvolume quotas:

    tux > sudo btrfs quota rescan -w /
  3. Show the data of the quota group (1/0 in the following example):

    tux > sudo btrfs qgroup show / | grep "1/0"
    1/0           4.80GiB    108.82MiB

    The third column shows the amount of space that would be freed when deleting all snapshots (108.82MiB).

To free space on a Btrfs partition containing snapshots you need to delete unneeded snapshots rather than files. Older snapshots occupy more space than recent ones. See Controlling Snapshot Archiving for details.

Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes, because a lot of data gets changed (package updates). Manually deleting these snapshots after they are no longer needed is recommended. See Section 7.5.4, Deleting Snapshots for details.

Can I Boot a Snapshot from the Boot Loader?

Yes—refer to Section 7.3, System Rollback by Booting from Snapshots for details.

How to make a snapshot permanent?

Currently Snapper does not offer means to prevent a snapshot from being deleted manually. However, you can prevent snapshots from being automatically deleted by clean-up algorithms. Manually created snapshots (see Section 7.5.2, Creating Snapshots) have no clean-up algorithm assigned unless you specify one with --cleanup-algorithm. Automatically created snapshots always either have the number or timeline algorithm assigned. To remove such an assignment from one or more snapshots, proceed as follows:

  1. List all available snapshots:

    tux > sudo snapper list -a
  2. Memorize the number of the snapshot(s) you want to prevent from being deleted.

  3. Run the following command and replace the number placeholders with the number(s) you memorized:

    tux > sudo snapper modify --cleanup-algorithm "" #1 #2 #n
  4. Check the result by running snapper list -a again. The entry in the column Cleanup should now be empty for the snapshots you modified.

Where can I get more information on Snapper?

See the Snapper home page at http://snapper.io/.