The expire command was designed mainly for deleting the contents of old backups, although it will work on any repository.

During expire, the tags daily, weekly, monthly and yearly will be assigned to the versions that are daily, weekly, monthly or yearly backups. The expire configuration will determine which version is - for instance - a monthly backup. It could be the first backup of the month, or the last backup of the month.

Finally, after all versions have been tagged according to the expire configuration, expire will mark versions deleted that shouldn’t be kept. For each daily/weekly/monthly/yearly backup, expire will keep the N newest backups, where N is configurable.

The expire/keep_daily setting defines how many daily backups expire will keep, the expire/keep_weekly setting defines how many weekly backups expire will keep, and so on. Finally the setting expire/keep_most_recent defines how many most recent backups expire will keep. Every backup that is not kept due to one of these settings will be marked deleted.

The settings that affect the expire command are documented in the "CONFIGURATION" section of bfsync(1).

Note that while expire marks versions as deleted, it doesn’t actually delete the file contents that belong to deleted versions. Running bfsync-gc(1) will delete all file contents that are only in deleted versions.