Intro to Rsync

rsync - a fast, versatile, remote (and local) file-copying tool
–rsync man page

As the man page suggests, rsync is a useful tool if you’re tired of cp-ing files around servers and managing the disastrous permissions aftermath. It has the ability to manage permissions, compress on-the-fly, and doesn’t waste time copying things that already exist in the destination.

Let’s say you have two folders, folder1 and folder2. These folders contain a very large amount of data, and right now they are the exact same. But let’s say you make a small change to folder1, like maybe adding a small file, or fixing a typo somewhere.

Without rsync, to ensure folder2 still contains an accurate copy, you have a couple options:

• Manually change folder2 the same way you did to folder1. To do this, you’d have to remember exactly what you did to folder1 each time you make a change. What happens when you have 4 or 5, or 100 copies of this folder? Assuming you had perfect memory and a lot of time, this solution still isn’t perfect, because the modification times on the files would be different.
• Remove folder2 and re-copy folder1. This would work, if the folders were small– but for our example, they’re not. cp-ing this folder could take hours.

Rsync is smart in that it only copies changes to your files. If we added one-small-file.txt to folder1 and ran rsync, it would only add one-small-file.txt to folder2 and call it a day- no need to re-copy the existing accurate files.

I run an Airsonic music server, which holds the “master copy” of some music I listen to. However, I prefer to keep local copies of this music on some of my machines, and so I find myself constantly having to keep all versions of this music the same across all my machines and server.

What about Git? Git is a version control system that would appear to solve this problem of concurrency; however, git works poorly for this use case.

With a single rsync command on each machine, I can pull down changes to the music folder to my local copy. This way, the copy on the server is the only one I have to manage.

bash

rsync --delete --recursive --compress --verbose user@domain.com:/remote/music/ /local/music/

Rsync is a versatile tool, and has a ton of capabilities I didn’t cover in this introduction. man rsync covers these and more.