---
title: "unison"
tags: [ "documentation", "backups", "sync" ]
---

Install unison on both machines, and on both make the `~/.unison` directory.

Make a job called `backup`:

> vim ~/.unison/backup.prf

All jobs must end in `.prf`.

Here is an example job, which synchronizes the `~/music` directory with a remote machine.

```
auto = true
root=/home/ghost
root=ssh://ghost@192.168.0.10//home/ghost/

path=music

ignore=Name *.flac

```
The last command means it will ignore any file with a name ending in `.flac`.

Add a port with this line:

```
sshargs=-p 4444
```

## Automatic Runs

The first command means this will run but also confirm which files will be deleted, and which will be transferred, us `batch = true` instead.

Set unison to run with crontab or a systemd unit file to have directories synchronize automatically.


## Problem Solving

Unison is extremely sensitive to version changes.
Both machines must have exactly the same version of unison installed, as well as the same version of `ocaml`.

Check with:

> unison -version

You will see data files summarizing what has happened in the `~/.unison` directory.
If something goes wrong, you may be prompted to delete these to start again.