Unison

What is Unison?

Unison is a mature file-synchronization tool originally developed in the early 2000s by The Unison Project. It runs natively on Linux, macOS, and Windows, and supports bidirectional sync over SSH, local disks, or network paths. Unlike simple one-way tools, Unison detects changes on both sides and helps resolve conflicts intelligently.

It's best suited for users who need reliable, scriptable synchronization between machines—like developers, system administrators, or anyone maintaining mirrored directories across devices. Its design favors precision and safety over flashy interfaces, making it ideal for technical users comfortable with configuration files and command-line workflows.

Compared to Windows tools like SyncBack, Unison feels more minimal and less GUI-driven. There’s no built-in scheduler or wizard-style setup. Instead, it relies on profiles and manual or scripted execution. If you're used to point-and-click sync tools, expect a steeper learning curve but greater control once set up.

Best for: Users who need precise, bidirectional sync between systems and don’t mind working with config files.

Key features of Unison

• Bidirectional file synchronization
• Supports local, remote (SSH), and network paths
• Detects and resolves two-way changes
• Cross-platform: Linux, macOS, Windows
• Preserves permissions, ownership, and symlinks
• Configurable conflict detection and handling
• Profile-based configuration system
• Runs in terminal or with GUI frontends

Tips for Windows users

If you're coming from SyncBack or Windows Live Sync, know that Unison doesn’t use the same project format. You’ll need to recreate sync jobs as text profiles. There are no drag-and-drop interfaces or automatic background monitoring—use inotify or cron to trigger runs. GUI tools like Unison-gtk help, but the real power is in scripting. SSH is the default remote method, so set up key-based authentication first.

Recent releases

• 2.54.0 — June 13, 2026

  - Drop old wire protocol. Unison will no longer interoperate with versions before 2.52.0 and will no longer read pre-2.52.0 archive files. - Document that LLM output is unwelcome in the Unison project (code, issues, mailinglists, etc.).

• 2.53.8-2 — April 6, 2026

  Switched to runtime version 25.08.

• 2.53.8 — January 10, 2026

  - Add ability to use reflinking instead of copying (if supported by filesystem). - Don't write file fingerprint cache if it is not necessary. - Experimental default-off support to detect moves/renames and rename on destination instead of copying (see…

• 2.53.7 — April 21, 2025

  First version on Flathub