Error: -69888: Couldn't unmount disk when installing Catalina

[harmtemolder]

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In the populate_bootable_installer_virtual_disk stage the /Volumes/bootinst-sh/bootinst.sh command in the Terminal results in the following:

Started partitioning on disk0
Unmounting disk
Error: -69888: Couldn't unmount disk

I found a reference to a deleted issue (#128) in #173 that mentions that same error, but nothing to solve it. What can I do to fix this?

Edit: I'm now trying HighSierra instead of Catalina and it looks like that one is working.

[myspaghetti]

I believe issue 128 was deleted after I couldn't reproduce the bug and the submitter didn't provide further information. I'll keep investigating this issue but currently I have no real direction for it.

[harmtemolder]

OK, no worries. I'm running High Sierra now without any problems, so not sure what the issue with Catalina is...

[Mechaniquake]

This happens when the installation is exited during function populate_basesystem_virtual_disk()

When the script is creating disk partitions and the machine pauses because of "low disk space" errors on VB: switching off the VM and restarting from the above function works up to the script again. Then the error occurs because it must come across the previous partitioning attempt.

The disk0 partition looks like it stores GPT JHFS+ (macOS_bootinst[.]txt shows it uses diskutil ) and probably can't be unmounted for that reason.