- A snapshot is considered outdated if its interval number is greater or
- equal than the specified number of unit intervals. See --unit-interval
- and --num-intervals above.
-
- A snapshot is said to be redundant if the interval it belongs to
- contains more than the configured number of snapshots.
-
- The prune command gets rid of both outdated and redundant snapshots. At
- most one snapshot is removed per invocation. If --dry-run is given, the
- subcommand only prints the snapshot that would be removed.
+ A snapshot is said to be (a) outdated if its interval number is greater
+ or equal than the specified number of unit intervals, (b) redundant if
+ the interval it belongs to contains more than the configured number of
+ snapshots, and (c) orphaned if it is incomplete and not being created
+ or deleted. All other snapshots are called regular.
+
+ Unless --dry-run is given, which just prints the snapshot that would be
+ removed, this subcommand gets rid of non-regular snapshots. At most
+ one snapshot is removed per invocation. If no such snapshot exists
+ and disk space is low, the subcommand also removes regular snapshots,
+ always picking the oldest one.
+
+ The subcommand fails if there is another dss "run" process.