After running into some problems with some rsync scripts recently, I discovered that in Mac OS 15.4, Apple switched its built-in rsync command from standard rsync to the BSD project’s clone, openrsync. It is apparently not 100% compatible, because my backup and deploy scripts that use it were failing.
I was running into errors like:
… copy_file dfd: openat: Too many open files …
… empty link …
… error: unexpected end of file …
… stat: No such file or directory …
that ultimately led to:
Backing up … failed.
and incomplete backups.
I still haven’t gotten all my scripts fully working and am trying to figure out what is wrong with them. My backup scripts use hard links for incremental snapshots via the --link-dest option, which doesn’t seem to work as well with openrsync. In particular, I have associated it with the Too many open files error on large backups. I saw some posts suggesting setting a high ulimit -n, but that didn’t work for me. I have disabled link-dest and just gone with simple sync for those scripts for now, which worked fine.
Also, I did a simple, one file local test of link-dest and for some reason I was getting a copy of the file every other run even when it wasn’t modified. I tried backup of the same file using openrsync with cp -l instead of link-dest for rotation and it copied the unmodified file every time with that, so maybe it’s just be something with APFS. Anyway, link-dest snapshotting may not be as space efficient as it could be.
Some of my sync scripts ran into the No such file or directory or empty link errors. Apparently, openrsync won’t blindly copy symlinks that have no destination. I had to remove some pointing to things that no longer existed and hide some from the sync that needed to be there.
Also, based on my search for fixes, openrsync may have problems with dirs without trailing slashes in exclude directives. I added trailing slashes to any dir-names in my exclude files.
Regular rsync can be installed using Homebrew (brew install rsync), which will give a much newer version than MacOS had. I may go this route to fix some of my regular user scripts. However, I have some backup scripts that must be run as root (backing up multiple user dirs and other stuff), and I don’t want to run “third-party” code with my root user. So, I may have to do more work to get link-dest snapshots working properly for those larger backups.