I don't think rsync fits your bill, because it won't automatically handle updates to the same document in multiple locations. The same is true for file deletions. You can do this manually, but this is bound to become problematic at some point.

I have never used unison, but it seems to be the right tool for your use case.

That said, I'd also like to mention distributed version control systems like Mercurial, Git, Bazaar, etc. They have the additional benefit that you don't lose old versions of your documents. They are, however, best suited for dealing with text files; binaries like LibreOffice documents and such will require more work when the same document is changed on several machines.

I don't think rsync fits your bill, because it won't automatically handle updates to the same document in multiple locations. The same is true for file deletions. You can do this manually, but this is bound to become problematic at some point.

I have never used unison, but it seems to be the right tool for your use case.

That said, I'd also like to mention distributed version control systems like Mercurial, Git, Bazaar, etc. They have the additional benefit that you don't lose old versions of your documents. They are, however, best suited for dealing with text files; binaries like LibreOffice documents and such will require more work when the same document is changed on several machines.

Update: If you want to have a real backup on the third machine, you should consider using a separate backup solution, because that will keep old files. rsync can do that as well (if you omit the --delete option), but this will again be problematic at some point: old files will fill up your document folders, and new files that have the same name as old, deleted files will overwrite them.

A simple backup system like dejadup, duplicity, rsnapshot, or rdiff-backup could be used for that.

I don't think rsync fits your bill, because it won't automatically handle updates to the same document in multiple locations. You can do this manually, but this is bound to become problematic at some point.

I have never used unison, but it seems to be the right tool for your use case.

That said, I'd also like to mention distributed version control systems like Mercurial, Git, Bazaar, etc. They have the additional benefit that you don't lose old versions of your documents. They are, however, best suited for dealing with text files; binaries like LibreOffice documents and such will require more work when the same document is changed on several machines.

I don't think rsync fits your bill, because it won't automatically handle updates to the same document in multiple locations. The same is true for file deletions. You can do this manually, but this is bound to become problematic at some point.

I have never used unison, but it seems to be the right tool for your use case.

That said, I'd also like to mention distributed version control systems like Mercurial, Git, Bazaar, etc. They have the additional benefit that you don't lose old versions of your documents. They are, however, best suited for dealing with text files; binaries like LibreOffice documents and such will require more work when the same document is changed on several machines.