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tarsnap wrapper which expires backups using a gfs-scheme.
Python
branch: master

README.rst

Tarsnapper

A wrapper around tarsnap which does two things:

  • Lets you define "backup jobs" (tarsnap invocations) in a config file, though on it's own this has little advantage over just using a a shell script.
  • The ability to expire old backups using a Grandfather-father-son backup scheme. This feature can be used in conjunction with tarsnapper backup jobs, or standalone, to be applied to any existing set of tarsnap backup archives, regardless of how they have been created.

Installation

Using easy_install:

$ apt-get install python-setuptools
$ easy_install tarsnapper

Using a configuration file

A configuration file looks like this:

# Global values, valid for all jobs unless overridden:
deltas: 1d 7d 30d
target: /localmachine/$name-$date

jobs:
  images:
    source: /var/lib/mysql
    exclude: /var/lib/mysql/temp
    exec_before: service stop mysql
    exec_after: service start mysql
    # Aliases can be used when renaming a job to match old archives.
    alias: img

  some-other-job:
    sources:
      - /var/dir/1
      - /etc/google
    excludes:
      - /etc/google/cache
    target: /custom-target-$date.zip
    deltas: 1h 6h 1d 7d 24d 180d

For the images job, the global target will be used, with the name placeholder replaced by the backup job name, in this case images.

You can then ask tarsnapper to create new backups for each job:

$ tarsnapper -c myconfigfile make

The name of the archive will be the target option, with the $date placeholder replaced by the current timestamp, using either the dateformat option, or %Y%m%d-%H%M%S.

Or to expire those archives no longer needed, as per the chosen deltas:

$ tarsnapper -c myconfigfile expire

If you need to pass arguments through to tarsnap, you can do this as well:

$ tarsnapper -o configfile tarsnap.conf -o v -c tarsnapper.conf make

This will use tarsnap.conf as the tarsnap configuration file, tarsnapper.conf as the tarsnapper configuration file, and will also put tarsnap into verbose mode via the -v flag.

Expiring backups

If you want to create the backups yourself, and are only interested in the expiration functionality, you can do just that:

$ tarsnapper --target "foobar-\$date" --deltas 1d 7d 30d - expire

The --target argument selects which set of backups to apply the expire operation to. All archives that match this expression are considered to be part of the same backup set that you want to operate on.

tarsnapper will then look at the date of each archive (this is why you need the $date placeholder) and determine those which are not needed to accomodate the given given delta range. It will parse the date using the python-dateutil library, which supports a vast array of different formats, though some restrictions apply: If you are using yyyy-dd-mm, it cannot generally differentiate that from yyyy-mm-dd.

You can specify a custom dateformat using the --dateformat option, which should be a format string as expected by the Python strptime function (e.g. %Y%m%d-%H%M%S). Usually, a custom format is not necessary.

Note the single "-" that needs to be given between the --deltas argument and the command.

The expire command supports a --dry-run argument that will allow you to see what would be deleted:

$ tarsnapper --target "foobar-\$date" --deltas 1d 7d 30d - expire --dry-run

How expiring backups works

The design goals for this were as follows:

  • Do not require backup names to include information on which generation a backup belongs to, like for example tarsnap-generations does. That is, you can create your backups anyway you wish, and simply use this utility to delete old backups.
  • Do not use any fixed generations (weekly, monthly etc), but freeform timespans.
  • Similarily, do not make any assumptions about when or if backup jobs have actually run or will run, but try to match the given deltas as closely as possible.

The generations are defined by a list of deltas. 60 means a minute, 12h is half a day, 7d is a week. The number of backups in each generation is implied by it's and the parent generation's delta.

For example, given the deltas 1h 1d 7d, the first generation will consist of 24 backups each one hour older than the previous (or the closest approximation possible given the available backups), the second generation of 7 backups each one day older than the previous, and backups older than 7 days will be discarded for good.

The most recent backup is always kept.

As an example, here is a list of backups from a Desktop computer that has often been running non-stop for days, but also has on occasion been turned off for weeks at a time, using the deltas 1d 7d 30d 360d 18000d:

dropbox-20140424-054252 dropbox-20140423-054120 dropbox-20140422-053921 dropbox-20140421-053920 dropbox-20140420-054246 dropbox-20140419-054007 dropbox-20140418-060211 dropbox-20140226-065032 dropbox-20140214-063824 dropbox-20140115-072109 dropbox-20131216-100926 dropbox-20131115-211256 dropbox-20131012-054438 dropbox-20130912-054731 dropbox-20130813-090621 dropbox-20130713-160422 dropbox-20130610-054348 dropbox-20130511-055537 dropbox-20130312-064042 dropbox-20120325-054505 dropbox-20110331-121745
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