One-way syncing/backup with Unison

Question

I'm using the syncing tool Unison with my Mac OSX and Ubuntu 9.10 machines to backup my music from Mac to Ubuntu. The thing is, I want to have my Mac be the source and Ubuntu be the target so that the Ubuntu machine will be an exact copy of the Music folder on the Mac at all times, but if I delete something from Ubuntu, it won't get deleted on the Mac. I've looked at the docs but it is kind of going over my head at the moment.

Answer 1

A better tool for the job might be rsync (you'll need to install it on both computers). I use it to keep my laptop music folder in sync with a home file server, which is pretty similar to your situation. rsync specializes in keeping a mirror copy up-to-date.

A command line like this might be useful (assuming you run it from Ubuntu):

rsync -a --delete-before myMacMachineName:/MyMusic/ /mymusic/

It is pretty easy to switch the above line around if you want to run it from your Mac and push to the Ubuntu computer instead of pulling.

Answer 2

Use unison -force:

Manual:

Including the preference -force root causes Unison to resolve all differences (even non-conflicting changes) in favor of root. This effectively changes Unison from a synchronizer into a mirroring utility. You can also specify -force newer (or -force older) to force Unison to choose the file with the later (earlier) modtime. In this case, the -times preference must also be enabled. This preference is overridden by the forcepartial preference. This preference should be used only if you are sure you know what you are doing!

E.g. (using socket mode). Start up unison listener in the directory that you want to be a mirror of something else. Target that socket in the unison client call. Force causes changes to be all ONE WAY from the given root.

cd /target/mirror/directory
unison -socket 123456 &

Elsewhere or on the same host:

unison -silent -force /home/test/thing2 /home/test/thing2 socket://somehost:123456/