Cannot erase disk to reinstall OS -"volume... in use by process 723 (kextcache)"

[Risible]

This 2015 MacBook Pro had only recently had a clean install (not by me) so nothing much more than my user name and a home folder has been added, but I now need to restore to how it was before I put my name in, to pass it on. Having set myself up as the User I am assuming that I can't just delete that account (correct?) and that I have to erase the disc and reinstall the OS.

I have followed the instructions on the Apple website. Using Disk Utility I deleted the 'Data' volumes first, but when I try to erase the main volume (which has been named 'Catalina'), I get this error message:View attachment 911712
'The volume "Catalina" on disk2s6 couldn't be unmounted because it is in use by process 689 (kextcache)
Couldn't unmount disk. : 9-69888)'

I have no idea what this means nor what to do next. Can anybody help? Thanks.

 

[Honza1]

I have never tried this, but erasing the system disk should not be necessary. That is write protected plain vanilla system and all user stuff is on data drive. Did you try to simply reboot?If Apple got it right, it should boot, recreate data disk and be clean running system... but that is only my expectation based on what is said about this disk schema. I did not have, luckily, chance to test it... please. Let us know.

 

[Xgm541]

Are you using recovery?

How to start up from macOS Recovery - Apple Support

macOS Recovery is the built-in recovery system of your Mac, with utilities to reinstall macOS, repair or erase your startup disk, restore from a Time Machine backup, and more.

support.apple.com

 

[Risible]

Thanks both. I am doing this in recovery mode. Soon after posting I did succeed in erasing the disk - simply by re-starting! (Apple's instructions said nothing about that); but if you are right Honza1, I needn't have bothered, and I now have to reinstall the OS unnecessarily. Hey ho.... It's good to learn.