Boxcryptor uses a kernel extension (kext) named "BCFS" to create the virtual Boxcryptor disk. It is a special version of the open source project OSXFUSE. Apple made significant changes to the loading of third party kernel extensions in macOS 11.0 Big Sur - and every big change almost always comes with some problems.
In this case, the macOS 11.0 Big Sur beta itself still contains various kernel extension related bugs, some of which are documented by Apple in the release notes:
Besides these documented Known Issues, Big Sur beta 4 also contains other kernel extension bugs - e.g. when loading a kernel extension, beta 4 always returns a success even if it actually failed. Despite the great brand and products, Apple is a software development company like many others and Big Sur beta 4 contains bugs just like any other pre-release software.
On "clean" Big Sur systems where Boxcryptor was never installed, the experimental version works mostly as expected. As far as we can tell until now, the "Mount Failed" errors reported here seem to be related to problems in the kernel extension loading mechanism of Big Sur if Boxcryptor was already installed in Catalina before the Big Sur upgrade. If you see this error, you can try the following options:
- First of all, make sure that you reboot your Mac and then try if the problem has been resolved. In some cases, a simple reboot was already the solution.
- Delete the legacy kernel extension from the Boxcryptor app bundle. Execute in the Terminal app:
sudo rm -rf /Applications/Boxcryptor.app/Contents/Frameworks/BoxcryptorFoundation.framework/Versions/A/Filesystems/bcfs.fs/Contents/Extensions/10.9
sudo rm -rf /Applications/Boxcryptor.app/Contents/Frameworks/BoxcryptorFoundation.framework/Versions/A/Filesystems/bcfs.fs/Contents/Extensions/10.10
- Reset third-party kernel extensions as described in Apple's workaround:
- Boot to macOS Recovery
- Run Terminal
- Enter the command
kmutil trigger-panic-medic --volume-root /Volumes/Macintosh\ HD
- If your boot volume has a different name than "Macintosh HD", replace it in the command above
- Restart your Mac
- Start Boxcryptor and re-approve the kernel extension by "Benjamin Fleischer" in the Security Preferences
- Restart your Mac (again)
- Manually load the kernel extension. Execute in the Terminal app:
sudo kmutil load -v -p /Applications/Boxcryptor.app/Contents/Frameworks/BoxcryptorFoundation.framework/Versions/A/Filesystems/bcfs.fs/Contents/Extensions/11.0/bcfs.kext
- If you have Virtual Box installed, there are reports that uninstalling it resolved kernel extension loading problems for other apps:
- Download VirtualBox installer package
- Run VirtualBox_Uninstall.tool from the down right corner
These workarounds can help in some cases, but maybe won't help in some others. Please remember that both macOS Big Sur beta 4 as well as our experimental version are still "work in progress" and are not final or stable versions. As a small anecdote: The first beta of Catalina featured a completely rewritten iCloud component. However, it was so unstable and buggy that Apple decided to completely revert this change and continue to use the "old" code in Catalina beta 7 ff. and the stable release.