Unison

A two-way file synchronizer for keeping a pair of directories in step across Windows, macOS, Linux and BSD hosts, usually over SSH.

5.6k stars, 279 forks OCaml On GitHub since February 2016

View on GitHub How to run it

Unison at a glance

Open sourceYes, GPL-3.0No paid parts in the repository
Health47 of 100Actively developed
Self-hostingmacOS, WindowsSteps in the README
AppsmacOS, Windows, including ARMBuilds in GitHub releases
InterfaceEnglish onlyNo translation files found
Issue repliesWithin ~2 hoursMedian first reply; 85% of recent issues answered

What is Unison?

Unison keeps two replicas of a directory tree, on different machines or different disks, up to date with each other. Either side can be changed independently; on the next run, non-conflicting edits flow both ways and conflicting ones are shown to you for a decision. It runs as an ordinary user program, with no kernel module, FUSE or root access needed, and talks over SSH or plain TCP. An rsync-like protocol sends only small changes to large files. Because data is copied rather than mounted, files stay usable offline. A repeat mode with a filesystem monitor syncs changes shortly after they happen.

Good fit if

  • You sync a laptop with a home server or VPS over SSH and want to resolve conflicts yourself.
  • You need two-way sync between Windows and Unix machines without a cloud service in between.

Look elsewhere if

  • You want continuous sync across many devices with automatic peer discovery: Syncthing.
  • You want a shared cloud with web access, sharing links and mobile apps: Nextcloud or Seafile.

Before you adopt it

Unison is distributed under GPL-3.0, and nothing in the repository is paid. The README estimates its upkeep at about 2.5 people and 0.1 full-time equivalents, so bug reports move slowly, and questions belong on the unison-users mailing list rather than the issue tracker. The project ships source code; CI builds exist for macOS and Windows, and Linux users usually rely on distribution packages. Only the newest release (v2.54.0 at the time of writing) is supported, while some distributions still carry far older versions.

Drafted with AI from the project's README and repository data, then checked against that data on 7 November 2026. Report a correction

How to run Unison yourself

One-click install

Not listed in the app catalogs of Umbrel, YunoHost, TrueNAS, Unraid, CasaOS, Runtipi, Proxmox VE Helper-Scripts and Coolify.

Ways to install

Docker files
None in the repository
Compose file
None in the repository
Setup effort
Not rated: no compose file to judge from
Kubernetes
No Helm chart in the repository
Packages
Debian, Ubuntu, Fedora, EPEL, Arch Linux, AUR, Alpine, openSUSE and 9 more versions on Repology
Desktop and mobile
Builds for macOS, Windows, including ARM in GitHub releases
Interface languages
English only

Install instructions: the README on GitHub. Docker images and packages are checked weekly.

Unison health: is it still maintained?

47 of 100, actively developed

Release rhythm1 release in 12 monthsLatest: v2.54.0, 1 May 2026
Issue repliesWithin ~2 hoursMedian first reply; 85% of recent issues answered
Bus factorMedium riskThe most active of 2 authors wrote 57% of recent commits
  • Activity
    7 commits in the last 90 days, the latest on 20 September 2026.
    11 / 30
  • Contributors
    2 people wrote the 7 commits of the last 90 days; the most active wrote 57% of them.
    6 / 20
  • Releases
    1 release in the last 12 months; the latest, v2.54.0, on 1 May 2026.
    7 / 20
  • Replies to issues
    Maintainers answered 85% of recent issues, with a median first reply after 2 hours.
    19 / 20
  • Security practices
    OpenSSF Scorecard 4.4 of 10.
    4 / 10

Read from GitHub on 12 November 2026. How the score works

Unison security

Security advisories are the vulnerabilities the maintainers disclosed on GitHub, with the versions that fix them; many advisories can mean careful disclosure as much as weak code. OpenSSF Scorecard checks how a project is developed and released: reviews, protected branches, pinned dependencies, signed releases. It does not audit the code itself.

Security advisoriesNone publishedNo advisories in the repository’s Security tab
OpenSSF Scorecard4.4 of 10How the project is built and released
Security policyNoNo SECURITY.md or similar
Signed releasesNoDownloads cannot be checked against a signature

What each Scorecard check found

  • Binary files10 / 10No compiled binaries checked into the repository
  • Dangerous workflows10 / 10No risky patterns in GitHub Actions
  • License file10 / 10A license file is present
  • Code review9 / 10Some changes are merged without review
  • Maintained7 / 10Some activity in the last 90 days
  • Best-practices badge0 / 10No OpenSSF Best Practices badge
  • Fuzzing0 / 10No fuzz testing found
  • Pinned dependencies0 / 10Dependencies are not pinned to fixed versions
  • Security policy0 / 10No security policy
  • Signed releases0 / 10Releases are not signed
  • Static analysis0 / 10No static analysis found
  • Token permissions0 / 10CI tokens have broad write rights

Advisories read from GitHub on 12 November 2026. From the OpenSSF Scorecard of 9 November 2026; checks that do not apply to Unison are left out.

Unison license: is it open source?

Unison uses GPL-3.0, an open-source license approved by the OSI.

  1. February 2016First published on GitHub.
  2. TodayGPL-3.0.

Unison for developers

Written in

  • OCaml 86%
  • Objective-C 6%
  • C 6%
  • Python 1%
  • Standard ML <1%
  • Other <1%

Getting involved

Contributing guideYesCONTRIBUTING.mdOpen issues93On GitHub
Authors, 90 days2Of 7 commits

Language shares are GitHub’s count of the code in the repository.

Alternatives to Unison

  • OpenCloudOpenCloud is the open source platform for file management, sharing and collaboration. Simple and sovereign. 79 health · Apache-2.0 · 6.3k stars
  • copypartyPortable file server with accelerated resumable uploads, dedup, WebDAV, SFTP, FTP, TFTP, zeroconf, media… 75 health · MIT · 47.3k stars
  • SyncthingOpen Source Continuous File Synchronization 69 health · MPL-2.0 · 90.4k stars
  • FileGatorPowerful Multi-User File Manager 67 health · MIT · 3.1k stars
  • CloudreveSelf-hosted file management and sharing system, supports multiple storage providers 54 health · GPL-3.0 · 29k stars

All 18 projects in File storage & sync

Questions about Unison

Is Unison open source?

Yes. Unison is published under GPL-3.0, an OSI-approved open-source license.

Is Unison still maintained?

Its health score is 47 of 100 (actively developed). It had 7 commits in the last 90 days, the latest on 20 September 2026, and its latest release came out on 1 May 2026.

How do I run Unison?

You can run it as an app for macOS, Windows, including ARM. The README on GitHub has the exact steps.

What is Unison written in?

Unison is written mainly in OCaml (86% of the code), with Objective-C (6%) and C (6%), by GitHub’s count of the repository.

What are the alternatives to Unison?

Close alternatives in the File storage & sync category include OpenCloud, copyparty, Syncthing.