- Upgrading a Mac from Catalina 10.15.6 to 10.15.7 failed with a dialog saying "An error occurred while generating the kernel cache" having "Restart" button.
- The Mac was no longer able to start in Safe Mode (seemed to cause a kernel panic).
- It could start in all Recovery Modes (⌘+R/option+⌘+R/Shift+option+⌘).
- But installing Catalina with retaining the user data ALWAYS failed with the same error in each Recovery Mode.
- It could not boot macOS in an external drive (ALWAYS failed)
- To clean-install Catalina to the Mac without losing the user data (Time Machine is not available)
- The Mac to be clean-installed => (A)
- External Drive (same or larger capacity of the Mac drive) => (B)
- Connect (B) to (A)
- Start (A) in Reocovery Mode (⌘+R)
- Open "Disk Utility"
- Choose (B) volume and click Restore
- Choose "Macintosh HD - Data" volume for a source
- Click Restore
- Shutdown after restoration
- Disconnect (B) from (A)
- Start (A) in Reocovery Mode (⌘+R)
- Open "Disk Utility"
- Choose a physical drive in (A)
- Click Erase to remove ALL volumes in the drive
- Quit "Disk Utility" then back to the recovery menu (macOS Utilities)
- Start "Reinstall macOS"
- Choose the erased drive for the destination
- Shutdown after the installation
- Connect (B) to (A)
- Start (A) without any modification keys
- Follow the instructions by the setup assistant and you can find "Migration Assistant" while the setup process.
- In "Migration Assistant", choose "From a Mac, Time Machine backup or startup disk" and coninue.
- Select (B) as a migration source.
- Select all folders to transfer and continue.
- After finishing the migration, the Setup Assistant asks you to set a password for the imported user.
- Enter Appl ID if necessary
- Then setup is done and Login screen appears. After logging in, you can see all apps and user data.