Unison File Synchronizer

I've been using Unison for over 15 years. I have my main desktop and 3 laptops. It has a simple GUI that shows which direction the file update will happen and lets me decide any conflicts if the same file has been modified in both places.

I, too, thought that Unison Cloud was somehow a backend for this.

Unison was one of the top tools to check for me. Unfortunately, its written in weird egghead language called Ocaml. It also support replicas, while I needed more p2p and VFS like aproach. So I wrote my simple DVFS repo manager in C instead. Very happy with the outcome. Maybe one day I will be brave enough to share it with the world ;)

Here is command summary: http://borg.uu3.net/~borg/?dot

Unison was huge while I was at Amazon, but I always preferred rsync for the control (sshfs too but you had to ensure to set some flags for when you de-docked or changed wifi ap). One of the biggest gripes I had with it is thankfully fixed though (used to need same client and server version, nowadays they permit some drift assuming no breaking contractual changes).

I'd also recommend setting up some ignore rules for build artifacts, etc, which definitely increases complexity but avoids constantly syncing build artifacts you don't care about or with erroneous symlinks etc. IDK at that point I figured rsync was easier, as it's a more commonly used tool for other purposes, and I'd rather learn fewer things with huge functional overlap if given the choice.

Performance has improved to the point where I no longer use it, but I know Unison was a critical part of docker-sync (at one point, file performance for Docker on Mac was absolutely terrible without it)

For what I tried is like rclone bisync but without cloud awareness. Useful in a LAN context and with all maturity one can ask for. Rare it hasn't got more good rap.

I haven't used Unison in a while, so maybe this isn't true anymore, but what always ended being the hangup for me was that both sides needed to use exactly the same version of Unison (IIRC at least down to the minor version number).

This ends up being a hassle unless you are using exactly the same OS on both sides, since you need to either have the right version in ports/apt/pacman/whatever or manage the Unison builds yourself.

Used this over ten years ago, for a few months. Absolutely loved it, but it was a pain to get the right version installed on different devices, and I think I once lost some data with it due to my own mistake.

Nowadays I use syncthing, which works quietly in the background and is really good at what I need. New pictures on my phone get synced to the laptop and backup server, while new pdfs on the laptop get synced with the phone and pinenote.

Sounds similar to https://syncthing.net/ ?

I'd like something like this for a three-copy backup solution. Regularly compare the three backups, and wherever one differs from the other two, correct the one with the minority opinion.

It seems like this must already exist but I don't know how to find it.

unison is wonderful, lesser known tool.

I used unison regularly for a few years around a decade ago to do bidirectional sync between a linux VM filesystem and a host windows filesystem, for a weird dev workflow where i would pig-headedly use linux tools to develop an application that would be built and shipped to windows.

I never had any trouble with unison, it was great.

That said, for that particular niche use case these days maybe I'd use WSL to get a similar job done -- or just do all development in Windows if that's the platform we were shipping to.

Warning, from the manual: Unison does not understand hard links.