upradge froze, not won't boot up
I followed the command to upgrade the OS, but it froze half way, then shut down, now it won't boot up to get into the old OS
MacBook Air (2018 or later)
Question marked as
Boot into Recovery (Command R) and from the dropdown menu: Utilities> Disk Utility> run the First Aid on your Macintosh HD. If errors are found and repaired, run again until no errors reported.
Recovery http://support.apple.com/kb/HT4718