macOS Catalina Known Issues

This documentation is for an older version of CCC. You can find the latest version here.
Last updated on December 30, 2020

Apple introduced a bug in 10.15.5 that prevents the creation of firmlinks

The chflags system call no longer works correctly on 10.15.5 with regard to setting the special "firmlink" flag that establishes links between the System and Data volume group members. If you're establishing a new backup of macOS 10.15.5 or later, CCC 5.1.17 (and earlier) will be unable to create a correctly-functioning APFS volume group. Many folders on the destination volume will appear empty, and the volume will not be bootable.

Solution: Update to macOS 10.15.6 and CCC 5.1.20.

We have reported this issue to Apple (FB7706647) and we are currently awaiting a response. Update: Apple resolved this issue in macOS 10.15.6. Apple made this "bug" a permanent change, however, in macOS Big Sur.

Some SMB volumes can't support macOS sparse disk images

We have received several reports that macOS is unable to create disk images on SMB volumes hosted by various NAS devices. If you attempt to create the disk image in Disk Utility (for example), Disk Utility reports an "RPC Error". After months of investigation, we have concluded that macOS Catalina has more stringent requirements for sparse disk images than previous OSes.

Solution: Several users have reported that adjusting the SMB configuration on the NAS to support Time Machine can resolve the problem. Time Machine also uses sparse disk images on NAS volumes, so its requirements for the NAS file sharing service would be the same as those required for generic sparse disk image support.

Workaround A: Several users are reporting that connecting to the network volume via AFP rather than SMB resolved the problem:

  1. Eject the NAS volume if it's currently mounted
  2. Choose "Connect to Server" from the Finder's Go menu
  3. Type in "afp://{server address}" to connect to the NAS volume via AFP
  4. Choose "New disk image..." from CCC's Destination selector and specify a new disk image on the AFP-mounted NAS volume

Workaround B: If connecting to your NAS volume via AFP is not an option, then you can back up user data (e.g. your home folder) directly to the NAS volume (i.e. don't use a disk image). We also recommend disabling support for extended attributes (via the Advanced Settings).

We recommend using NAS devices for secondary backups. For primary backups, we recommend that you procure a USB or Thunderbolt hard drive and create a bootable backup on that locally-attached disk. Local, bootable backups are much simpler and more reliable, and a lot easier to restore from should your Mac's startup disk fail. The logistics of restoring the operating system from a disk image on a network volume are pretty complicated if you don't have a functional startup disk. Providing that functional startup disk is the primary appeal of the CCC backup solution.

2012-vintage Macs can't boot macOS Catalina from an encrypted USB device

We have received several reports that the 2012 Mac mini and the 2012 MacBook Pro can initially boot from a non-encrypted external USB device, but then will fail to boot from that device when FileVault is enabled on the external device. This issue is not specific to CCC, we have confirmation that this occurs when installing Catalina directly onto an external device as well. This problem does not appear to be specific to any particular enclosure, rather it appears to be specific to the 2012 models of Mac mini and MacBook Pro.

We have reported this issue to Apple (FB7433465) and we are currently awaiting a response.

macOS Catalina will not boot from a FireWire device

Apple has dropped support for booting from FireWire devices. The macOS Catalina Installer will explicitly disallow installation onto a FireWire-attached device, and if you attempt to boot macOS Catalina from a FireWire-attached device, the startup process will fail with the universal "no entry" symbol.

Solution: If your external device also has a USB interface, attach the device to your Mac using a USB cable instead.

Workaround: If your external device does not have a USB interface, you can continue to make backups to that device, but they will not be bootable while that device is attached via Firewire. If you need to restore data from this backup, you can either place the external hard drive into a different hard drive enclosure, or you can migrate the data to a fresh installation of macOS Catalina via the Migration Assistant application. If you prefer to maintain bootable backups, you should purchase an enclosure that will be bootable with macOS Catalina. We offer specific hard drive recommendations here.

Emerging issue: Higher incident rate of macOS Catalina failure to boot from Western Digital My Passport enclosures

We have received several reports now of Western Digital My Passport hard drive enclosures failing to function as a startup disk with macOS Catalina. In all cases the end user was able to confirm that the macOS Installer was also unable to make the device bootable. The results are inconsistent — in some cases the system proceeds approximately 75% into the startup process, then shuts down. In other cases the system transparently boots to the internal disk, and in other cases (probably most) the enclosure boots fine. Due to the number of cases of confirmed failed bootability, however, we discourage users from purchasing new WD My Passport HDD enclosures if your intent is to create a bootable macOS Catalina backup. Please note that the WD My Passport SSD is NOT included among these reports. WD My Passport enclosures with a rotational HDD should be avoided.

Specific hard drive recommendations

Mount issues render USB thumb drives unsuitable for bootable backups

We have discouraged the use of thumb drives in the past due to performance and reliability issues related to making these devices bootable. In the past the macOS loginwindow service has prevented CCC from mounting the APFS helper partitions on these devices. Now that the Catalina System and Data volumes are also special APFS volumes, we're seeing the same sort of interference from the loginwindow service, although now it leads to failures in backing up the Data volume. We are no longer offering support for these devices as bootable backups. You're welcome to create a non-bootable backup of your Catalina Data volume instead:

  1. Open CCC and click the Show Sidebar button in CCC's toolbar if it is not already visible
  2. Select your backup task in the sidebar
  3. Drag the Macintosh HD - Data volume from CCC's sidebar into the Source selector
  4. Save the task

Startup Disk Preference Pane doesn't show OS versions for external volumes

The System Preferences application lacks full disk access by default, so it cannot read the System Version file on external volumes for the purpose of presenting the system version string underneath the volume icons. Ironically, System Preferences has the privilege to change the startup disk, but it can't make a read-only access to the system version file on external volumes.

Solution: Open System Preferences > Security & Privacy > Privacy, click the padlock icon and authenticate when prompted, then add the System Preferences application to the Full Disk Access category.

We have reported this issue to Apple (FB6723060) and we are currently awaiting a response.

Spotlight's "mds" helper aggressively prevents volume unmount requests

During our Catalina testing we repeatedly had trouble unmounting volumes in Disk Utility, particularly when erasing a backup volume. Upon closer inspection we found that an mds process is nearly always the process that is preventing the unmount. We've seen this occasionally in the past, and for a long time CCC's option to unmount the destination volume at the end of a backup task has worked around the occasional Spotlight dissent with a followup forced-unmount. In Catalina, however, the problem seems to be far worse, affecting nearly every casual unmount attempt (except in the Finder, oddly).

Workaround for general unmount annoyances: You can disable Spotlight on your CCC backup volume to avoid its interference (and for better performance in general). To disable Spotlight, open the Spotlight preference pane in the System Preferences application, click on the Privacy tab, then drag the backup volume into the Privacy table. This only affects the destination volume, and it's reversible, you can remove it from that list should you decide that you want to re-enable indexing.

Workaround when attempting to erase a volume: If you're trying to erase a volume in Disk Utility and Disk Utility is reporting that it cannot unmount the volume to erase it — brace yourself for this one — unmount the volume before erasing it. That's right, Disk Utility can't walk and chew gum at the same time. If you unmount the volume before erasing it, though, the unmount request typically succeeds and you are then able to erase the volume.

We have reported this issue to Apple (FB6905679) and we are currently awaiting a response.

Apple's volume group manipulation tool doesn't work with encrypted volumes

To create a bootable backup of a macOS Catalina volume, CCC must create a volume group at the destination. If your existing destination is a FileVault-protected volume (e.g. container a backup of Mojave), that destination can't be converted into a volume group — Apple's diskutil utility will fail, e.g.:

apple@Apollo ~ % diskutil ap addVolume disk8 APFS "CCC Backup" -passphrase apple -groupWith disk8s1 -role S
Will export new encrypted APFS Volume "CCC Backup" from APFS Container Reference disk8
Started APFS operation on disk8
Preparing to add APFS Volume to APFS Container disk8
Error: -69475: You cannot request initial encryption while creating a new APFS Volume to be added to an APFS Volume Group

Considering the error message, this appears to be intentional behavior. However, we have submitted an enhancement request Apple (FB7418398) and we are currently awaiting a response.

Workaround: You can temporarily decrypt your destination volume or erase it as APFS, then re-enable FileVault after establishing the initial backup of macOS Catalina.

Related documentation

Disk Utility fails to create a volume group on T2 Macs when the startup disk is encrypted

Similar to the issue described above, we have discovered an edge case in which Disk Utility fails to create an APFS volume group on the internal SSD of a T2 Mac when the current startup disk is encrypted. The typical scenario in which we see this is when the Mac is booted from an encrypted backup volume, and the user is attempting to restore the backup to the freshly-erased internal SSD. Unlike the issue described above, this failure occurs when the destination is not encrypted — it appears to be specific to the current startup disk being encrypted, which seemingly should not play a role at all in the creation of a volume group on an unrelated device.

We have reported this issue to Apple (FB7477894) and we are currently awaiting a response.

Workaround A: Decrypt the backup volume

We don't want to even suggest this solution given the hassle that most users have had to endure to get their backups re-encrypted after the Catalina upgrade, but this will effectively work around the bug in Disk Utility:

  1. Boot your Mac from the backup volume
  2. Disable FileVault in the Security & Privacy Preference Pane
  3. Wait for decryption to complete
  4. Reboot — this step is important
  5. Perform the restore and reset the startup disk
  6. Re-enable FileVault on the backup volume, then reboot from the restored internal disk

Workaround B: Boot your Mac from another macOS Catalina volume that is not encrypted

The problem is not specific to the backup volume that you would like to restore from, rather Disk Utility only fails when the current startup disk is encrypted. If you can boot your Mac from another non-encrypted startup disk, you can restore your encrypted backup volume to the internal disk of your T2 Mac.

When you eject the destination in the Finder, Finder prompts to unmount other volumes that you can't see

When you make a bootable backup of a macOS Catalina system volume, the destination will consist of two volumes arranged in a volume group. Finder shows only one of these volumes, but both volumes are mounted as a pair. When you ask the Finder to eject your destination volume, Finder will indicate that other volumes on that device are mounted, and will ask if you want to unmount all volumes:

"CCC Backup" is a volume on a disk that has 2 volumes. Do you want to eject "CCC Backup" only, or both volumes?

Finder doesn't tell you the identity of the other volume, which makes the decision a bit difficult to make. Rest assured, though, that the other volume is the hidden Data volume associated with your backup. You should unmount both volumes to avoid any Finder admonitions when you physically detach the backup disk from your Mac.

Solution: Click the Eject All button when prompted to unmount both the System and Data volumes.

We have reported this issue to Apple (FB7422542) and we are currently awaiting a response.

Finder will not show, nor allow you to set custom icons on other Catalina startup disks

Finder will show and allow you to customize the volume icon for your current startup disk, but not for other Catalina-bearing startup disks that your Mac is not currently booted from. This problem is not specific to CCC backups, but we see this frequently because CCC is designed to create bootable backups. This problem is the result of a design flaw in the implementation of custom icons in an APFS volume group. Up to macOS Catalina, the custom volume icon is stored in a file at the root of the startup disk named ".VolumeIcon.icns". To keep the System volume read-only, yet allow the apparent modification of this icon file, Apple chose to create a symbolic link at the root of the startup disk that points System/Volumes/Data/.VolumeIcon.icns. For the current startup disk, this path resolves correctly because the Data member of the volume group is mounted at /System/Volumes/Data. That's not the case for external volumes, those Data volumes are mounted at /Volumes/CCC Backup - Data (for example). As a result, the symbolic link to .VolumeIcon.icns is unresolvable for any volume that is not the current startup disk.

We have reported this issue to Apple (FB7697349) and we are currently awaiting a response.

Resolved Issues

On login, macOS fails to unlock and mount the Data volume of an encrypted APFS volume group

If you have an installation of macOS Catalina on a separate volume (e.g. a backup disk) and FileVault is enabled on that volume, the prompt to unlock the volume only unlocks the System volume. If the Data volume is not unlocked and mounted, the volume does not work correctly and the bulk of your data will appear to be missing.

Workaround: You must manually mount the Data volume in CCC (or Disk Utility) to get access to your data on the backup: Right-click the Data volume in CCC's sidebar and choose Mount.

We have reported this issue to Apple (FB6786776) and we are currently awaiting a response.

Update: This issue appears to be resolved in Catalina Beta 7.

The APFS filesystem causes a kernel panic when remounting the System volume in an encrypted APFS volume group

If you unmount and then remount the System volume (or sometimes when you then unmount the System volume again) in an encrypted APFS volume group, the system will kernel panic. CCC will only need to mount or unmount the System volume of the backup disk during a backup task if changes have been made to the source System volume (e.g. after applying a software update). If a kernel panic occurs, simply re-run the backup task after the system reboots to complete the backup.

Partial mitigation: Disabling Spotlight on the destination appears to reduce the incidents of kernel panics. To disable Spotlight, open the Spotlight preference pane in the System Preferences application, click on the Privacy tab, then drag the backup volume into the Privacy table. This only affects the destination volume, and it's reversible, you can remove it from that list should you decide that you want to re-enable indexing.

Update: This issue appears to be resolved in Catalina Beta 9.

System Preferences cannot enable FileVault on external volumes

This is an emerging issue as of Catalina Beta 6. When attempting to enable FileVault on an external volume (whether it is a backup or an installation placed there by the Installer), the FileVault preference pane claims:

FileVault Failed [sic]
This operation is restricted by your settings in System Preferences > Security & Privacy > Privacy > Files and Folders.

The meaning of this dialog is ambiguous, and you can't actually make configuration changes in the "Files and Folders" category. In fact, the problem is not that you have misconfigured something in "Files and Folders", rather some component of the Security Preference Pane, or a service that it relies upon to enable FileVault lacks access to external volumes (i.e. "Full Disk Access"). The identity of that service is not made clear by this dialog.

We have reported this issue to Apple (FB7083306) and we are currently awaiting a response.

Update: This issue appears to be resolved in Catalina Beta 7.