Since the introduction of macOS Catalina 10.15.5 back in May backup programs Carbon Copy Cloner and Super Duper have been unable to create bootable backups due to a bug in macOS.

For Carbon Copy Cloner there was a workaround available in version 5.1.18, while for Super Duper it was necessary to contact the developer to work around the problem.

Now, with the arrival of macOS Catalina 10.15.6, Apple has finally fixed the bug. Super Duper works again as it should, and there is an update for Carbon Copy Cloner (version 5.1.20).

Our original story from 29 May 2020 follows:

macOS 10.15.5 has fixed some problems but it appears it has created others. The developer behind a backup tool is disappointed that the latest update to macOS Catalina is causing problems for customers using his backup tool.

Mike Bombich, the developer behind Carbon Copy Cloner - the popular tool for creating backups and bootable system copies - says the latest Catalina update to version macOS 10.15.5 causes major problems with backups.

A system copy created with an older version of CCC is no longer bootable and does not appear to contain any data. According to Bombich, this is due to an obvious bug in the current version of macOS. The bug had already occurred in the beta version of 10.15.5 but wasn’t addressed prior to release.

Carbon Copy Cloner

The problem seems to be that in order for a newly created system copy to boot, the backup tool must change a so-called flag of a folder with the system call chflag. However, if you want to set the "SF_FIRMLINK" flag, this will fail for an APFS folder under macOS 10.15.5. There is no error message, which makes it difficult to detect the error. Without this flag, which activates so-called firm links, the system copy is neither bootable nor does it appear to contain the saved data.

Luckily if your backup was created under an older version of macOS will remain bootable.

A new beta version of Carbon Copy Cloner that enables the creation of bootable copies under macOS 10.15.5 has already been made available. This version - beta 5.1.18 - uses Apple's ASR tool in the background instead of the backup engine previously used. ASR is currently the only program that can create bootable system copies.

For Bombich this is only an emergency solution, since the tool offers fewer functions and is more prone to errors than his self-developed software. Other third-party backup programs such as Super Duper may also be affected by the problem.

The developer, who has already informed Apple about the error, is quite upset that such an obvious system error could occur in what is, after all, the fifth Catalina update. "It's hard to find kind words to express my feelings towards Apple right now. Suffice it to say, though, I'm extremely disappointed that Apple would introduce this kind of bug in a dot-release OS update."

According to Bombich, Apple did not intend to introduce new restrictions for backup software, it was simply an error.

In addition to introducing this bug the macOS Catalina update improves battery health and fixes a Finder crash bug. Find out about the problems and issues with Catalina as well as the new features here.

This article originally appeared on Macwelt. Translation by Karen Haslam.