Linux rsync Command Guide: Incremental File Synchronization Across Folders and Drives

Introduction to rsync for Incremental File Synchronization

The rsync command is a powerful file synchronization and backup tool for Linux. It uses a delta-transfer algorithm to perform incremental synchronization, transferring only the parts of files that have changed between the source and destination. This makes it highly efficient for saving bandwidth and time. A common use case is incrementally syncing files from a mounted directory of an old hard drive (e.g., /mnt/old_disk/) to a mounted directory of a new hard drive (e.g., /mnt/new_disk/).

Basic rsync Command for Incremental Sync

The following command performs an incremental sync from directory A to directory B, excluding specific directories:

rsync -av --exclude lost+found/ --exclude backup/ ./A/ ./B

Command Parameter Breakdown

• -a: Archive mode. Equivalent to -rlptgoD. It enables recursive copying and preserves permissions, timestamps, and other attributes.
• -v: Verbose mode. Outputs a list of files being processed during the sync.
• --exclude: Excludes files or directories matching the given pattern. The example excludes the system directory lost+found/ and a user backup directory backup/.
• ./A/: The source directory path. The trailing slash (/) means sync the contents of the directory, not the directory itself.
• ./B: The target directory path.

Important Notes and Best Practices

1. Path Specification: Replace ./A/ and ./B with absolute paths (e.g., /mnt/disk_a/ and /mnt/disk_b) based on your actual mount points to avoid ambiguity.
2. First-Time Sync: If the target directory B is empty, this command copies all files. If it already contains data, rsync performs an incremental update.
3. Delete Synchronization: To make the target directory an exact mirror of the source (deleting files in the target that don't exist in the source), add the --delete option. Use this with extreme caution.
4. Dry Run: Add the -n option (e.g., rsync -avn ...) to perform a simulation. This previews the operations without actually copying any files.

Tip: Before performing any sync operation involving important data, always run a dry run with -n and double-check your target paths to prevent data loss.