Introducing duplicity-nfs-backup, or How to Use duplicity-backup Safely with NFS/CIFS Shares

After completing nfs_automount script a bit over a week ago, I soon realized rdiff-backup I had planned to use with the now-nearly-guaranteed-to-be-online NFS shares would not work. I then turned to my other favorite *NIX server backup solution, duplicity with wrapper script. It utilizes gzip-based archives, which works much better with NFS/CIFS shares. Besides the other odd problems with rdiff-backup and NFS, it resolves the more obvious issue with conflicting users/permissions between the client and the NFS share host as duplicity doesn’t maintain a direct mirrored copy of the files being backed up.

The only problem was that since duplicity creates incrementals, and I generally like to keep backups around for several months, the incrementals are really never needed beyond couple of weeks. Beyond that in my applications the day-by-day backups are overkill, and should be pruned. Duplicity provides an option to do so (“remove-all-inc-of-but-n-full”), but hadn’t implemented it, so I first contributed a patch to zertrin’s project. Then I proceeded to write a wrapper for the wrapper to add the extra pre-backup checks, and duplicity-nfs-backup was born.

So what is duplicity-nfs-backup? It is a wrapper script designed to ensure that an NFS/CIFS-mounted target directory is indeed accessible before commencing with backup. While can be used to back up to a variety of mediums (ftp, rsync, sftp, local file…), duplicity-nfs-backup is specifically intended to be used with NFS/CIFS shares as backup targets.

The script that was the impetus for writing duplicity-nfs-backup, nfs_automount, attempts to keep the NFS shares online at all times, but the client system can’t always help with such situations. What if the target system becomes unreachable due to a network problem? Or what if a disk, or a filesystem mount fails on the target while the share is still available? In any of these cases duplicity-backup/duplicity would back up into an empty mountpoint. duplicity-nfs-backup adds the necessary checks to ensure that this won’t happen, and it also issues log/syslog warnings when a backup fails due to a share that has gone M.I.A.

I mentioned earlier that duplicity-nfs-backup is “a wrapper for the wrapper.” Paraphrasing zertrin, it is important to note that duplicity-nfs-backup IS NEITHER duplicity, NOR is it duplicity-backup! It is only a wrapper script for duplicity-backup, also written in bash.

This means that you will need to install and configure duplicity and before you can utilize duplicity-nfs-backup. I also recommend that you would make use of nfs_automount as it significantly improves the chances that the NFS target share will be online when duplicity-nfs-backup attempts to access it.

This script is intended to be run from crontab. duplicity-nfs-backup takes no arguments, simply set the configuration parameters in duplicity-nfs-backup.conf and you’re done!

Like nfs_automount, duplicity-nfs-backup is also distributed under MIT license.

Clone or download duplicity-nfs-backup from my GitHub repository, and let me know if you come across any problems (or also if it works fantastically and saves the day! :)). Pull requests are always welcome.

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