Compare files and attributes by checksum, using rsync(1) in dry-run
mode with all preserve options enabled.
Resolves snapshot/backup pairs by evaluating the output of
"btrbk list latest [filter...]".
Restrictions:
- ".d..t...... ./" lines are ignored by default:
Root folder timestamp always differ.
- "cd+++++++++ .*" lines are ignored by default:
Nested subvolumes appear as new empty directories.
- btrbk raw targets are skipped
- rsync needs root in most cases (see --ssh-* options)