In a report published last week, MacOS 15.4 made a significant change by replacing the utility rsync with the alternative implementation openrsync, developed by the OpenBSD project. The executable file /usr/bin/rsync in MacOS now refers to Openrsync. This decision was likely influenced by recently identified security issues in rsync, a desire to reduce components with licenses, and the need to eliminate the outdated version of rsync that cannot be updated due to licensing policies.
Openrsync is characterized by its focus on high security during development, code distribution under the ISC license (BSD family) instead of the GPL license for rsync, and the use of a different internal architecture (one process for accepting and sending data using the event processing cycle). While openrsync is compatible with rsync at a basic level, it does not support all command line options, only those most popular for file synchronization and backups.
Considering that the outdated version of rsync 2.6.9, released in November 2006, did not significantly impact functionality, the decision to transition to openrsync was deemed feasible. The choice of rsync 2.6.9 was based on its distribution under the GPLv2+ license, with subsequent releases such as rsync 3.0 moving to the GPLv3 license which prohibits tivoization, the practice of binding software to specific equipment.