btrfs-snap

btrfs-snap creates and maintains the history of snapshots of btrfs filesystems.

Features:

• can snapshot inside of the filesystem or rooted in a base directory
• can purge old snapshots when too many exist
• can keep multiple snapshot schedules for the same filesystem

btrfs-snap is designed to be called from cron on a regular schedule.

Usage

btrfs-snap [-r] [-b basedir] mountpoint prefix count

• mountpoint is the filesystem to snapshot
• prefix is the prefix, which usually corresponds to a schedule (e.g. 1m, 5m, 3h, 1d, 1w, 3mo)
• count is the number of snapshots with the same prefix to keep
• -r makes the snapshot readonly (requires btrfs-tools v0.20)
• -c generates more compatible snapshot names (ie. no colons that confuse SAMBA/Window$ clients)
• -E treats omitting of snapshots as error
• -p redefines the prefix to be used as postfix
• -d dir places the snapshot in dir, relative to the mountpoint
• -b basedir places the snapshot in basedir with a directory structure that mimics the mountpoint
• -B basedir places the snapshots in basedir with NO additional subdirectory structure
• -t/-T time creates only a snapshot if the newest already existing snapshot is older than 'time' seconds.
• -q output becomes cron-compatible: silent unless an error occurs.

Without -b, -B, or -d, snapshots are placed in a directory called .snapshot at the top of the mountpoint.

mountpoint must be a mounted btrfs filesystem (i.e. appears in the output of "mount -t btrfs") or an unmounted btrfs subvolume (which must exit 0 when "btrfs su sh" is called on it). Unmounted subvolumes require a recent version of btrfs-progs; see "OS Support" below for specifics.

Examples

*/5   *   *   *   *   btrfs-snap -r / 5m 12
0     0   *   *   *   btrfs-snap -r -b /snapshots /home 1d 7

The above cronjob would

1. create a snapshot of / every 5 minutes, keeping 12 generations in /.snapshot
2. create a snapshot of /home every day, keeping 7 generations in /snapshots/home

OS Support

Tested on

• Ubuntu 12.04 with the raring kernel
• Ubuntu 13.04
• Debian 8
• Debian 9

Anything else, YMMV. Reports of successful use on other operating systems is welcome

To snaphshot an unmounted btrfs subvolume, you need a version of btrfs-progs that supports the "btrfs subvolume show" command.

The version that comes with Ubuntu 13.04 is too old; the version that comes with Ubuntu 13.10 works. You should be able to compile a working version from the sources (refer to https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories for details).

License

This program is distributed under the GNU General Public License

http://www.gnu.org/licenses/gpl.txt

Authors

Originally by Birger Monsen birger@birger.sh

Readonly and basedir additions by James FitzGibbon james@nadt.net

VFS snapshot naming support by gitmopp (https://github.com/gitmopp)

Support for snapshotting unmounted btrfs subvolumes by Brian Kloppenborg (https://github.com/bkloppenborg)

Switches -c (for windows-combitible timestamps) and -d (for specifying the snapshot directory) by Lukas Pirl (btrfs-snap@lukas-pirl.de)

Switches -B (absolute path of snapshot directory) and -t/-T (time-dependent snapshot) by Michael Walz (btrfs-snap@serpedon.de)