Unison File Synchronizer

Version: 2.40.63 || Release Date: 2011-04-11 || License: GPL Developer: Benjamin Pierce | App Owner: brab

Unison is a file-synchronization tool for Unix (including OS X) and Windows. It allows two replicas of a collection of files and directories to be stored on different hosts (or different disks on the same host), modified separately, and then brought up to date by propagating the changes in each replica to the other.

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10 Opinions

Great software. I'm pleasantly surprised at how easy it is to set up powerful multi-machine syncing. And it's free. Thank you!

I apologize for hogging bandwidth here, but it seems worth emphasizing that Unison is just a fantastic program. I use it almost daily. After years of hype about the glorious future world of network computing, I've become cynical over how hard it still is, how often, just to get two devices to see each other over a local network, and how dangerous automated back-up stuff can still be. The effectiveness of Unison is spooky: it works the way the hype said everything would. It's like finding you can download a free jetpack.

janglinus: you are definitely right, we should document this. In the meantime, clicking on any entry will give you some information in the bottom that detail the states of both files, which could help you figure out what the changes are. Here is a quick description of the icons:
circle filled with blue: changed file
circle filled with gray: unchanged file
gray circle filled with white: absent file (it is not there and was not there before)
green circle with plus: new file (it is there and was not there before)
red circle with x: deleted file (it is not there but was there before)
~: permission change (they are orthogonal to contents change)

Hope this helps,


The 2.27 beta seems to work fine in Leopard. I was still using 2.24, which I thought was the latest version available here when I posted. Anyway, now the only problem I have is that the upgraded Mac GUI doesn't seem to be documented. It looks great, but I wish I knew what it all meant. It's mostly self-explanatory, but it actually took me a little while to be sure that left/right still meant local/remote. And I still can't find out what all the little circular icons mean. I think they indicate what kinds of discrepancies exist, with 'x' meaning a file has been deleted, and + meaning it has been created. But the blue dot and the tilde have me baffled.

janglinus: what version did you use? Did you try the 2.27.47 beta? Or the text version?

Unfortunately none of the developers is using Leopard yet. It may be just a question of recompiling, which requires installing OCaml and XCode. If someone wants to give it a try, please contact me at [email protected]

Seems to be broken in Leopard. It won't get through the firewall, but that's fine. The problem is that even if I turn firewalls off on both machines, then Unison connects as it should and the filenames all flash by as it checks for differences to reconcile. But then instead of giving me the list of differences and letting me start reconciling, the window is empty and all the control icons except Quit and Restart are greyed out.

Update after several weeks of daily use: it still works great. It does, quite rarely, crash or disconnect without obvious cause. But after experiencing this now half a dozen times, I have had no adverse consequences. Just connect again and finish the sync, and everything's fine.

I have just started using this, but so far it works great. It's amazingly fast, for what it does, especially after the first time with a new profile. Setting up a profile requires some TextEdit on your .prf file, which doesn't seem to be possible through the GUI. But there are some nice tutorials on the web, and it's really pretty simple.

I use it to keep work data on my laptop backed up to my corporate server and to keep my personal data on my laptop synched to my home computer. I can work on either home or work computers and synch the changes back to my laptop.