backup timeshift

This is a small script that backups btrfs snapshots organized in a Timeshift structure to another place. This can be used to backup the snapshots to a different drive. Whenever possible the script will copy the snapshots incremental. All @* folders under the <ROOT> folder are considered snapshots.

Example <ROOT>

The following figure shows an example layout:

<ROOT>
├── 2021-05-06_02-03-24
│   └── @
├── 2021-05-16_17-24-47
│   ├── @
│   └── @home
..............
└── 2021-05-17_00-57-13
    ├── @
    └── @home

To copy the snapshots to an arbitray destination <DEST> execute:

backup_btrfs_timeshift --root=<ROOT> --destination=<DEST>

Mounting destination

If your destination is another drive and you want to make sure it was properly mounted (so you don't just copy the snapshots into a "normal" folder) it is advisable to use the --force-mount option.

Implementation

1. If --force-mount option was set or the <DEST> doesn't exist yet, try to mount <DEST> (See man fstab on how to configure mount for this behaviour)
2. Search for all possible @* folders at second level.
3. For each possible @* subvolume candidate, search all folders (subdir) at first level if they contain said candidate:
   1. Search for orphaned readonly snapshots (pendant in <ROOT> got deleted) and delete them at <ROOT> and <DEST> (unless --no-delete specified)
   2. Create a readonly snapshot copy at <ROOT>/../readonly/subdir because only they can be send via btrfs send
   3. Sync readonly snapshot to <DEST>/snapshots/subdir. (Incremental sync is automatically applied in find order)

TODOs

• dry-run option