On many Unix-based operating systems, rsync is a command line tool for transferring and synchronizing files on a computer, either between storage attached directly to the computer or between another computer located elsewhere on a network. The rsync command line tool has long been included on macOS, but Apple has provided the last version of rsync 2.x (rsync 2.6.9, released in November 2006) and did not update rsync past that even though rsync 3.x was released. Why not? It has to do with the version of the GNU General Public License (GPL) open source license that rsync 2.x and 3.x were released under, with rsync 2.x being released under the GPLv2 license and rsync 3.x being released under the GPLv3 license. Without going in-depth into the background legal issues, the reason for not providing rsync 3.x is that Apple decided that while it could comply with the terms of GPLv2 license with regards to rsync 2.x, it could not comply with the terms of GPLv3 license with regards to rsync 3.x.

What this has meant for macOS is that it has been shipping with a version of rsync which was last updated in 2006. While Apple has been updating the rsync 2.6.9 command line tool it shipped with macOS as needed in response to security issues and other problems, the fact remains that Apple’s version of rsync up until macOS Sequoia was almost twenty years old and did not include any of the new features introduced in rsync versions which came after version 2.6.9.

Now with macOS Sequoia, Apple has replaced rsync 2.6.9 with openrsync, which is an implementation of rsync which is not using any version of the GPL open source license. Instead, opensync is licensed under the BSD family of licenses, specifically the ISC license. The ISC license is a permissive license, which means it places minimal restrictions on on how the licensed software can be used, modified and distributed, which means Apple decided it is able to comply with the terms of the license for openrsync where it decided it could not comply with the terms of GPLv3 license with regards to rsync 3.x.

So I’ve spent a bunch of time talking about licenses. Why does this change matter? It matters in two ways:

1. Apple can ship updated versions of openrsync going forward without having to be concerned as to whether or not Apple can comply with the GPL open source license for rsync.
2. The openrsync command line tool is compatible with rsync, but as noted in the documentation openrsync accepts only a subset of rsync’s command line arguments.

Item number 2 is important for Mac admins because it may mean that rsync functionality that worked on older versions of macOS may not be working now on macOS Sequoia because that functionality is not available as part of the openrsync command line tool included with macOS Sequoia. For more information about what functionality is supported in the openrsync command line tool on macOS Sequoia, please see the link below:

https://manp.gs/mac/1/openrsync

As of macOS 15.4, the openrsync tool is linked to /usr/bin/rsync so you can run the the openrsync command line tool like you have been the rsync command line tool. For version information about the openrsync command line tool, run the command shown below:

You should see output similar to that shown below: