unison

Install unison on both machines, and make sure both have the same version of unison, with the same version of the ocaml compiler (the smallest difference will cause problems).

unison -version

Create the ~/.unison directory on both machines.

Make a job called backup:

JOB=backup

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

echo "
auto = true
root=$HOME
root=ssh://$USER@$IP_ADDRESS/$HOME

path=music

ignore=Name *.flac
" > ~/.unison/"$JOB".prf

Remember to specify $IP_ADDRESS

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

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. Or you can deleted that line in the .prf file and run it with a flag:

unison -batch *backup*.prf

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

Problem Solving

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.