linkdest

Linkdest refers to the --link-dest option in the rsync file synchronization tool. It enables the use of hard links to files from a reference directory when creating a new destination directory, enabling space-efficient incremental backups. When a file in the source directory has the same content as a corresponding file in the link-dest directory, rsync creates a hard link in the destination to the file in the link-dest instead of copying the file again.

How it works: During a transfer, rsync compares the source with the link-dest baseline. For files that are identical in both locations, it creates a hard link in the destination to the existing file in the link-dest. For files that differ, rsync copies the new version to the destination as a separate inode, so changes are preserved without affecting the reference backup. This mechanism is commonly used to implement incremental backups while keeping a complete, navigable history.

Usage: A typical invocation is rsync -a --link-dest=/path/to/previous-backup /source/ /backup/new/ . The link-dest directory should be on the same filesystem as the destination to permit hard links. You can perform successive backups by pointing --link-dest to the most recent backup each time, producing a sequence of backups that share unchanged data.

Limitations and considerations: The feature relies on hard links, so both the source and link-dest (and the destination) must reside on the same filesystem. It does not deduplicate across unrelated backups automatically; each new backup depends on a correctly chosen link-dest baseline. Permissions, attributes, and symlinks are preserved according to rsync settings.