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Determine candidates and delete from a set of directories containing aging backups.
As a follow up to the release of sayebackup.sh last December, here’s a complimentary tool we’re using at Lanedo. Suppose a number of backup directories have piled up after a while, using sayebackup.sh or any other tool that creates time stamped file names:

 drwxrwxr-x etc-2010-02-02-06:06:01-snap
 drwxrwxr-x etc-2011-07-07-06:06:01-snap
 drwxrwxr-x etc-2011-07-07-12:45:53-snap
 drwxrwxr-x etc-2012-12-28-06:06:01-snap
 drwxrwxr-x etc-2013-02-02-06:06:01-snap
 lrwxrwxrwx etc-current -> etc-2012-12-28-06:06:01-snap

Which file should be deleted once the backup device starts to fill up?
Sayepurge parses the timestamps from the names of this set of backup directories, computes the time deltas, and determines good deletion candidates so that backups are spaced out over time most evenly. The exact behavior can be tuned by specifying the number of recent files to guard against deletion (-g), the number of historic backups to keep around (-k) and the maximum number of deletions for any given run (-d). In the above set of files, the two backups from 2011-07-07 are only 6h apart, so they make good purging candidates, example:

 $ sayepurge.sh -o etc -g 1 -k 3
 Ignore: ./etc-2013-02-02-06:06:01-snap
 Purge:  ./etc-2011-07-07-06:06:01-snap
 Keep:   ./etc-2012-12-28-06:06:01-snap
 Keep:   ./etc-2011-07-07-12:45:53-snap
 Keep:   ./etc-2010-02-02-06:06:01-snap

For day to day use, it makes sense to use both tools combined e.g. via crontab. Here’s a sample command to perform daily backups of /etc/ and then keep 6 directories worth of daily backups stored in a toplevel directory for backups:

/bin/sayebackup.sh -q -C /backups/ -o etc /etc/ && /bin/sayepurge.sh -q -o etc -g 3 -k 3

Let me know in the comments what mechanisms you are using to purge aging backups!


The GitHub release tag is here: backups-0.0.2
Script URL for direct downloads: sayepurge.sh


Usage: sayepurge.sh [options] sources...
  --inc         merge incremental backups
  -g <nguarded> recent files to guard (8)
  -k <nkeeps>   non-recent to keep (8)
  -d <maxdelet> maximum number of deletions
  -C <dir>      backup directory
  -o <prefix>   output directory name (default: 'bak')
  -q, --quiet   suppress progress information
  --fake        only simulate deletions or merges
  -L            list all backup files with delta times
  Delete candidates from a set of aging backups to spread backups most evenly
  over time, based on time stamps embedded in directory names.
  Backups older than <nguarded> are purged, so that only <nkeeps> backups
  remain. In other words, the number of backups is reduced to <nguarded>
  + <nkeeps>, where <nguarded> are the most recent backups.
  The puring logic will always pick the backup with the shortest time
  distance to other backups. Thus, the number of <nkeeps> remaining
  backups is most evenly distributed across the total time period within
  which backups have been created.
  Purging of incremental backups happens via merging of newly created
  files into the backups predecessor. Thus merged incrementals may
  contain newly created files from after the incremental backups creation
  time, but the function of reverse incremental backups is fully
  preserved. Merged incrementals use a different file name ending (-xinc).

See Also

Sayebackup.sh - deduplicating backups with rsync

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