# Removing backup snapshots

All backup space is finite, so restic allows removing old snapshots. This can be done either manually (by specifying a snapshot ID to remove) or by using a policy that describes which snapshots to forget. For all remove operations, two commands need to be called in sequence: `forget` to remove a snapshot and `prune` to actually remove the data that was referenced by the snapshot from the repository. This can be automated with the `--prune` option of the `forget` command, which runs `prune` automatically if snapshots have been removed.

Warning

Pruning snapshots can be a very time-consuming process, taking nearly as long as backups themselves. During a prune operation, the index is locked and backups cannot be completed. Performance improvements are planned for this feature.

It is advisable to run `restic check` after pruning, to make sure you are alerted, should the internal data structures of the repository be damaged.

## Remove a single snapshot

The command `snapshots` can be used to list all snapshots in a repository like this:

    $ restic -r /srv/restic-repo snapshots
    enter password for repository:
    ID        Date                 Host      Tags  Directory
    ----------------------------------------------------------------------
    40dc1520  2015-05-08 21:38:30  kasimir         /home/user/work
    79766175  2015-05-08 21:40:19  kasimir         /home/user/work
    bdbd3439  2015-05-08 21:45:17  luigi           /home/art
    590c8fc8  2015-05-08 21:47:38  kazik           /srv
    9f0bc19e  2015-05-08 21:46:11  luigi           /srv

In order to remove the snapshot of `/home/art`, use the `forget` command and specify the snapshot ID on the command line:

    $ restic -r /srv/restic-repo forget bdbd3439
    enter password for repository:
    removed snapshot d3f01f63

Afterwards this snapshot is removed:

    $ restic -r /srv/restic-repo snapshots
    enter password for repository:
    ID        Date                 Host     Tags  Directory
    ----------------------------------------------------------------------
    40dc1520  2015-05-08 21:38:30  kasimir        /home/user/work
    79766175  2015-05-08 21:40:19  kasimir        /home/user/work
    590c8fc8  2015-05-08 21:47:38  kazik          /srv
    9f0bc19e  2015-05-08 21:46:11  luigi          /srv

But the data that was referenced by files in this snapshot is still stored in the repository. To cleanup unreferenced data, the `prune` command must be run:

    $ restic -r /srv/restic-repo prune
    enter password for repository:

    counting files in repo
    building new index for repo
    [0:00] 100.00%  22 / 22 files
    repository contains 22 packs (8512 blobs) with 100.092 MiB bytes
    processed 8512 blobs: 0 duplicate blobs, 0B duplicate
    load all snapshots
    find data that is still in use for 1 snapshots
    [0:00] 100.00%  1 / 1 snapshots
    found 8433 of 8512 data blobs still in use
    will rewrite 3 packs
    creating new index
    [0:00] 86.36%  19 / 22 files
    saved new index as 544a5084
    done

Afterwards the repository is smaller.

You can automate this two-step process by using the `--prune` switch to `forget`:

    $ restic forget --keep-last 1 --prune
    snapshots for host mopped, directories /home/user/work:

    keep 1 snapshots:
    ID        Date                 Host        Tags        Directory
    ----------------------------------------------------------------------
    4bba301e  2017-02-21 10:49:18  mopped                  /home/user/work

    remove 1 snapshots:
    ID        Date                 Host        Tags        Directory
    ----------------------------------------------------------------------
    8c02b94b  2017-02-21 10:48:33  mopped                  /home/user/work

    1 snapshots have been removed, running prune
    counting files in repo
    building new index for repo
    [0:00] 100.00%  37 / 37 packs
    repository contains 37 packs (5521 blobs) with 151.012 MiB bytes
    processed 5521 blobs: 0 duplicate blobs, 0B duplicate
    load all snapshots
    find data that is still in use for 1 snapshots
    [0:00] 100.00%  1 / 1 snapshots
    found 5323 of 5521 data blobs still in use, removing 198 blobs
    will delete 0 packs and rewrite 27 packs, this frees 22.106 MiB
    creating new index
    [0:00] 100.00%  30 / 30 packs
    saved new index as b49f3e68
    done

## Removing snapshots according to a policy

Removing snapshots manually is tedious and error-prone, therefore restic allows specifying which snapshots should be removed automatically according to a policy. You can specify how many hourly, daily, weekly, monthly and yearly snapshots to keep, any other snapshots are removed. The most important command-line parameter here is `--dry-run` which instructs restic to not remove anything but print which snapshots would be removed.

When `forget` is run with a policy, restic loads the list of all snapshots, then groups these by host name and list of directories. The grouping options can be set with `--group-by`, to only group snapshots by paths and tags use `--group-by paths,tags`. The policy is then applied to each group of snapshots separately. This is a safety feature.

The `forget` command accepts the following parameters:

- `--keep-last n` never delete the `n` last (most recent) snapshots
- `--keep-hourly n` for the last `n` hours in which a snapshot was made, keep only the last snapshot for each hour.
- `--keep-daily n` for the last `n` days which have one or more snapshots, only keep the last one for that day.
- `--keep-weekly n` for the last `n` weeks which have one or more snapshots, only keep the last one for that week.
- `--keep-monthly n` for the last `n` months which have one or more snapshots, only keep the last one for that month.
- `--keep-yearly n` for the last `n` years which have one or more snapshots, only keep the last one for that year.
- `--keep-tag` keep all snapshots which have all tags specified by this option (can be specified multiple times).
- `--keep-within duration` keep all snapshots which have been made within the duration of the latest snapshot. `duration` needs to be a number of years, months, days, and hours, e.g. `2y5m7d3h` will keep all snapshots made in the two years, five months, seven days, and three hours before the latest snapshot.

Multiple policies will be ORed together so as to be as inclusive as possible for keeping snapshots.

Additionally, you can restrict removing snapshots to those which have a particular hostname with the `--hostname` parameter, or tags with the `--tag` option. When multiple tags are specified, only the snapshots which have all the tags are considered. For example, the following command removes all but the latest snapshot of all snapshots that have the tag `foo`:

    $ restic forget --tag foo --keep-last 1

This command removes all but the last snapshot of all snapshots that have either the `foo` or `bar` tag set:

    $ restic forget --tag foo --tag bar --keep-last 1

To only keep the last snapshot of all snapshots with both the tag `foo` and `bar` set use:

    $ restic forget --tag foo,bar --keep-last 1

All the `--keep-*` options above only count hours/days/weeks/months/years which have a snapshot, so those without a snapshot are ignored.

For safety reasons, restic refuses to act on an “empty” policy. For example, if one were to specify `--keep-last 0` to forget all snapshots in the repository, restic will respond that no snapshots will be removed. To delete all snapshots, use `--keep-last 1` and then finally remove the last snapshot ID manually (by passing the ID to `forget`).

All snapshots are evaluated against all matching `--keep-*` counts. A single snapshot on 2017-09-30 (Sat) will count as a daily, weekly and monthly.

Let’s explain this with an example: Suppose you have only made a backup on each Sunday for 12 weeks. Then `forget --keep-daily 4` will keep the last four snapshots for the last four Sundays, but remove the rest. Only counting the days which have a backup and ignore the ones without is a safety feature: it prevents restic from removing many snapshots when no new ones are created. If it was implemented otherwise, running `forget --keep-daily 4` on a Friday would remove all snapshots!

Another example: Suppose you make daily backups for 100 years. Then `forget --keep-daily 7 --keep-weekly 5 --keep-monthly 12 --keep-yearly 75` will keep the most recent 7 daily snapshots, then 4 (remember, 7 dailies already include a week!) last-day-of-the-weeks and 11 or 12 last-day-of-the-months (11 or 12 depends if the 5 weeklies cross a month). And finally 75 last-day-of-the-year snapshots. All other snapshots are removed.