Retention Policy Enforcement

System Message: ERROR/6 (/home/lf/src/backy2/benji/docs/source/enforce.rst, line 10)

Command 'benji enforce --help' failed: [Errno 2] No such file or directory: 'benji': 'benji'

Benji supports a simple but flexible mechanism for retention policy enforcement. Enforcement is done per version name, i.e. a specific policy is applied to all versions with the same name. Enforcement is not automatic and has to be initiated with benji enforce.

This Benji command is just for policy enforcement (i.e. thinning out versions by removal over time). You have to adjust your schedule to match your policy. For example, if you want to keep hourly backups for the last 72 hours (hours72) you have to create a new version at least every hour.

Filter expressions (see section Filter Expressions) are used to select the versions the specified policy is applied to.

benji enforce supports machine readable output (see section Machine output). All removed versions are listed and could be aggregated into a report for example.

Attention

Enforcement will remove any version which doesn’t match the policy. To exclude versions from enforcement protect them with benji protect.

Policy Specification

The enforcement policy is specified as a comma separated list of time categories:

  • latest (always refers to the youngest versions, regardless of how old they are)

  • hours

  • days

  • weeks

  • months

  • years.

Each time interval is directly followed by a positive number, no whitespace is allowed. The categorization (except for latest) follows natural time boundaries, i.e. the groups of versions formed by the hours category each start at the full hour. The same goes for months where each group starts at the first of each month at 00:00 and for years where each group starts at January 1st, 00:00. Each group of the weeks category starts on Monday at 00h00.

Attention

Times are based on the timezone which is set when benji enforce is called. Ensure that each invocation of benji enforce uses the same timezone. Otherwise some additional versions might get deleted because of the time shift.

Examples:

  • latest3,hours48,days7,weeks4,months12,years3

    • Keep the youngest three versions regardless of their age

    • Then keep one version per hour for the last 48 hours

    • Then keep one version per week for the last four weeks

    • Then keep one version per month for the last twelve months

    • Then keep one version per year for the last three years

  • years3,months12,latest2

    • Keep the youngest two versions

    • Then keep one version per month for the last twelve months

    • Then keep one version per year for the last three years

  • hours72

    • Keep one version per hour for the last 72 hours

  • latest10

    • Keep the youngest ten versions

Even when you specify the time categories in a different order, they are always considered from youngest to oldest (see the second example).

You can call benji enforce as many times a day as you want. If no version currently falls into a specified category the oldest version of the category below it is always kept, so that it has a chance to get old enough. So if in the third example there is one version which is older than 24 hours but younger than one year it will be kept till it is old enough even though it falls out of the first specified category.

If there is overlap between two categories the younger category always takes precedence.