Do backups using rsnapshot on the occasions the backup media is available
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Occasional rsnapshot

This is a tool that allows automatic backups using rsnapshot when the external backup drive or remote backup media is connected.

Although the ideal setup would be to have periodic backups on a system that is always online, this is not always possible. But when the connection is done, the backup should start fairly quickly and should respect the daily/weekly/... schedules of rsnapshot so that it accurately represents history.

In other words, if you backup to an external drive or to some network/internet connected storage that you don't expect to have always connected (which is is case with laptops) you can use occasional_rsnapshot to make sure your data is backed up when the backup storage is connected.

occasional_rsnapshot is appropriate for:

  • laptops backing up on:
    • a NAS on the home LAN or
    • a remote or an internet hosted storage location
  • systems making backups online (storage mounted locally somehow)
  • systems doing backups on an external drive that is not always connected to the system

The only caveat is that all of these must be mounted in the local file system tree somehow by any arbitrary tool, occasional_rsnapshot or rsnapshot do not care, as long as the files are mounted.

So if you find yourself in a simillar situation, this script might help you to easily do backups in spite of the occasional availability of the backup media, instead of no backups at all. You can even trigger backups semi-automatically when you remember to or decide is time to backup, by simply pulging in your USB backup HDD.


Install rsnapshot and make sure your rsnapshot configuration file contains the stanza below so no backup is tried when the backup media is not mounted:

no_create_root	1

Note: rsnapshot.conf uses tabs as separators between the option and the value, so copying the line above from this file into your rsnapshot.conf might not yeld the expected results.

Then run occasional_rsnapshot with the 'rsnapshot.conf' file as parameter.

occasional_rsnapshot /path/to/rsnapshot.conf

Note: Optionally, if you want to check first what would be done, you can pass the --debug option and see what decisions occasional_rsnapshot would make. When using this option rsnapshot will not be called at all.

occasional_rsnapshot --debug /path/to/rsnapshot.conf

occasional_rsnapshot tries to find snapshot_root based on the information in the configuration file, then, if found, it analyzes its contents and based on the options in the rsnapshot.conf file and the status of the snapshot_root, it starts the appropriate backups which are detected as necessary, for all the enabled intervals.

If occasional_rsnapshot does not find snapshot_root directory, it will terminate silently, since it assumes the backup media is not mounted.

Run via cron

Copy the script to an appropriate place and add a line simillar to this to your crontab for automatic running:

*/5 *   *   *  *    /home/eddy/bin/occasional_rsnapshot /home/eddy/etc/rsnapshot/local.conf

This will run the script every 5 minutes.

The script is smart enough to exit silently when appropriate:

  • when other instance of rsnapshot for the same config file is running
  • when the drive is not connected
  • when the time passed since the last backup is not above the minimum interval set by the rsnapshot configuration file

This means that the script does the right thing at all times, even if called repeatedly.

Encryption and advanced setups

Since rsnapshot uses rsync for the backup and rsync does not encrypt the files on the backup media, a way to implement encrypted backups is to encrypt the source files which rsnapshot backups.

You can use encfs --reverse to transparently obtain an ecrypted version of your source filesystem. After that, change your backup stanzas in rsnapshot.conf to do backups of the encypted versions of your files instead of the originals.

Since the original filenames will not be available/visible to rsnapshot, if you want to exclude specific files from the backup, you will have to filter those files by other means than the exclude rsnapshot.conf stanzas. This can be achieved by a filtering filesystem such as the filterfs FUSE filesystem (or, if you run GNU/Hurd, a filtering translator).

In essence, when using encfs and filterfs, the resulting setup would be:

      Occasional Rsnapshot
|  Filtered and ecrypted files  |
|           (encfs)             |
|        Filtered files         |
|          (filterfs)           |
|        Original files         |

encfs is available in most distributions or can be downloaded from .

Unfortunately the filterfs fuse filesystem upstream doesn't seem to be active anymore, but since I used this for this exact setup, a more recent version with some fixes can be grabbed from:


  1. Because the script is silent by default when no drive is found, it makes it appropriate for placing in cron with a very high frequency as a means of triggering backups by just connecting the backup drive or mounting the backup media; no noise will be made in the cron emails when the script does not find the backup drive connected.

  2. When passing --debug the script is verbose and does not invoke rsnapshot at all.


Development of occasional_rsnapshot happens on github at:

Patches and pull requestst are welcome.


This project uses Semantic Versioning

For short, here is what that means:

Given a version number MAJOR.MINOR.PATCH, increment the:

MAJOR version when you make incompatible API changes,
MINOR version when you add functionality in a backwards-compatible manner, and
PATCH version when you make backwards-compatible bug fixes.