APFS Bug in macOS 10.15.5 Catalina Impacts the Creation of Bootable Backups

An Apple File System bug has been discovered in macOS 10.15.5 Catalina that can prevent users from making a bootable clone of their system drive, according to the creator of Carbon Copy Cloner.

macos volumes icones
In a blog post on Wednesday, software developer Mike Bombich explained that the CCC team had uncovered the issue in the Apple File System, or APFS, when attempting to create a bootable backup in a beta version of macOS 10.15.5.

According to Bombich, the bug prevents CCC from using its own file copier to establish an initial bootable backup of a macOS Catalina System volume. In technical terms:

The chflags() system call can no longer set the SF_FIRMLINK flag on a folder on an APFS volume. Rather than fail with an error code that we would have detected, it fails silently – it exits with a success exit status, but silently fails to set the special flag. That's a bug in the APFS filesystem implementation of chflags – if a system call doesn't do what you ask it to do, it's supposed to return an error code, not success.

We don't need to set many of these flags, nor set them frequently – just on the first backup of the macOS system volume. It happens to be essential to the functionality of an APFS volume group, though, so the failure to set these flags means that new full-system backups created on 10.15.5 and later won't be bootable, and it will appear as if none of your data is on the destination (to be clear, though, all of the data is backed up). Kind of the opposite of what we're trying to do here. 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. We've seen 5 major updates to Catalina now, we should expect to see higher quality than this from an operating system.

On a positive note, existing backups created in macOS 10.15.4 and earlier are unaffected, the bug has no effect on CCC's ability to preserve data, nor does it affect the integrity of the filesystems on a startup disk or a backup disk. In short, the impact of this bug is limited to the initial creation of a bootable backup.

Any CCC users who established their backup on a previous version of Catalina already has functional firmlinks on their bootable volume and CCC will continue to update that volume just fine. Meanwhile, users wanting to create a new backup of a 10.15.5 volume to an empty disk should replace their copy of CCC with the CCC 5.1.18 beta, then follow these steps on launching the app.

  1. Click the X button in the Destination selector box to clear the destination selection.
  2. Click on the Destination selector and reselect the destination volume.

CCC will then guide users through the procedure of creating a bootable backup, or a Data-only backup instead. The new functionality uses Apple's Software Restore (ASR) utility.

Bombich has notified Apple of the bug, but he ends his blog post by entertaining the possibility that it is a security fix to prevent third-parties from creating firmlinks. If so, he argues, "this is far worse than a bug," since the system currently reports a success when it should report a failure, not to mention that Apple's lack of documentation on the change is hostile to third-party developers who rely on documented functionality.

Related Forum: macOS Catalina

Popular Stories

Generic iOS 19 Feature Mock Light

iOS 19 Leak Reveals All-New Design

Friday January 17, 2025 2:42 pm PST by
iOS 19 is still around six months away from being announced, but a new leak has allegedly revealed a completely redesigned Camera app. Based on footage it obtained, YouTube channel Front Page Tech shared a video showing what the new Camera app will apparently look like, with the key change being translucent menus for camera controls. Overall, the design of these menus looks similar to...
2024 iPhone Boxes Feature

Apple Changes Trade-In Values for iPhones, iPads, Macs, and More

Thursday January 16, 2025 6:45 am PST by
Apple today adjusted estimated trade-in values for select iPhone, iPad, Mac, and Apple Watch models in the U.S., according to its website. Some values increased, while others decreased. The changes were not too significant, with most values rising or dropping by $5 to $50. We have outlined some examples below: Device New Value Old Value iPhone 15 Pro Max Up to $630 U ...
2024 App Store Awards

Apple Explains Why It Removed TikTok From the App Store in the U.S.

Sunday January 19, 2025 6:58 am PST by
Apple on late Saturday removed TikTok from the App Store in the U.S., and it has now explained why it was required to take this action. Last year, the U.S. passed a law that required Chinese company ByteDance to divest its ownership of TikTok due to potential national security risks, or else the platform would be banned. That law went into effect today, and companies like Apple and Google...
Generic iOS 18

Everything New in iOS 18.3 Beta 3

Thursday January 16, 2025 12:39 pm PST by
Apple provided the third beta of iOS 18.3 to developers today, and while the betas have so far been light on new features, the third beta makes some major changes to Notification Summaries and also tweaks a few other features. Notification Summary Changes Apple made multiple changes to Notification Summaries in response to complaints about inaccurate summaries of news headlines. For...
iOS 19 Roundup Feature

iOS 19 Rumored to Be Compatible With These iPhones

Saturday January 18, 2025 10:28 am PST by
iOS 19 will not drop support for any iPhone models, according to French website iPhoneSoft.fr. The report cited a source who said iOS 19 will be compatible with any iPhone that can run iOS 18, which would mean the following models: iPhone 16 iPhone 16 Plus iPhone 16 Pro iPhone 16 Pro Max iPhone 15 iPhone 15 Plus iPhone 15 Pro iPhone 15 Pro Max iPhone 14 iPhon...
iPad Pro vs iPhone 17 Air Feature

Here's How Thin the iPhone 17 Air Might Be

Friday January 17, 2025 3:38 pm PST by
For the last several months, we've been hearing rumors about a redesigned version of the iPhone 17 that Apple might call the iPhone 17 "Air," or something along those lines. It's going to replace the iPhone 17 Plus as Apple's fourth iPhone option, and it will be offered alongside the iPhone 17, iPhone 17 Pro, and iPhone 17 Pro Max. We know the iPhone 17 Air is going to be super slim, but...
airtag 4 pack blue

AirTag 2 Launching This Year With These 3 New Features

Sunday January 19, 2025 8:11 am PST by
After a four-year wait, a new AirTag is finally expected to launch in 2025. Below, we recap rumored upgrades for the accessory. A few months ago, Bloomberg's Mark Gurman said Apple was aiming to release the AirTag 2 around the middle of 2025. While he did not offer a more specific timeframe, that means the AirTag 2 could be announced by the end of June. The original AirTag was announced...
apple power beats pro 2

Powerbeats Pro 2 Coming Soon: Apple to Announce Them 'Imminently'

Sunday January 19, 2025 8:25 am PST by
In September, Apple said that it would be launching Powerbeats Pro 2 in 2025, and it appears the wireless earbuds are coming very soon. Powerbeats Pro 2 images found in iOS 18 code In his Power On newsletter today, Bloomberg's Mark Gurman said the Powerbeats Pro 2 are "due imminently." In addition to Apple filing the Powerbeats Pro 2 in regulatory databases last month, Gurman said Apple is...

Top Rated Comments

weup togo Avatar
61 months ago

so outside of people trying to steal Apple IP to load newer MacOS versions on older systems or create hack-instoshes it must be a very small community of people that's affected by this.
this is so offensively dumb, I can’t find the words
Score: 113 Votes (Like | Disagree)
ikir Avatar
61 months ago

A bug in Catalina? No way! Apple makes both the hardware and the software so things work flawle… ?
Just use Windows for one week and macOS will be perfect again. Believe me I’m an IT and half week I’m working for a big company with everything Microsoft related. HELL ON EARTH.
Score: 40 Votes (Like | Disagree)
bchah Avatar
61 months ago
I don't comment often, but when I do... it is to confirm that if Mike Bombich is saying this is a problem, then this is a problem.
Score: 38 Votes (Like | Disagree)
star-affinity Avatar
61 months ago
A bug in Catalina? No way! Apple makes both the hardware and the software so things work flawle… ?
Score: 36 Votes (Like | Disagree)
superiska123 Avatar
61 months ago

Just use Windows for one week and macOS will be perfect again. Believe me I’m an IT and half week I’m working for a big company with everything Microsoft related. HELL ON EARTH.
This is so accurate! Catalina is a truly terrible release, but I seriously cannot comprehend the praise Microsoft gets for Windows 10... In my experience as a software developer, macOS is still miles ahead of Windows.
Score: 21 Votes (Like | Disagree)
MacDevil7334 Avatar
61 months ago
Wow what is going on with Apple’s software QC process these days? I have never sat out an entire MacOS release before. I thought 10.15.5 would finally be stable enough to get me to upgrade from Mojave. But apparently not. And iOS 13 still has bugs that have been present since the first beta (looking at you, Mail). Something is really broken over at Apple right now.
Score: 18 Votes (Like | Disagree)