administratormacos
My Mac used to have 2 Admin accounts:
Admin1 is now missing. How can I recover Admin1? Admin2 doesn't have the rights to create another account. Guest account is also turned off.
You can create a new administrator account by restarting the Setup Assistant:
Boot into Single User Mode: Start/restart your Mac. As soon as you hear the startup tone, press and hold ⌘ + S until you see a black screen with white lettering. (If you end up back on the login screen after a flash of the black screen with white lettering, enter your password and it will return to the black screen.)
Check and repair the drive by typing /sbin/fsck -fy then ↩ enter - as directed by the on-screen text.
Mount the drive as read-write by typing /sbin/mount -uw / then ↩ enter.
Remove the Apple Setup Done file by typing
rm /var/db/.AppleSetupDone then ↩ enter.
Reboot by typing reboot then ↩ enter.
Complete the setup process, creating a new admin account.
Note that this may result in the new account being logging in automatically when the system is restarted, replacing whatever account may have been set to automatically log in previously. If you need to retain access to the original account without knowing its password, this may mess that up.
After some extensive testing (and multiple Time Machine restores--to verify that this fix works), I have found a solution. And it's pretty easy too, just don't do it on the go, or you'll wipe out your battery.
Poof! Guest is gone.
And that's it! It works nicely with FileVault 2, Bootcamp, and Time Machine, so no worries there.
Best Answer
This happens all the time. Upgrades don't intentionally delete any user data, but when you have corruption, upgrade time is when major changes cause you to rewrite data on disk and loss is checked or noticed.
You can restore from a backup or make a backup of what is now on the disk and then try an erase install. If you are missing something as large as a user account, who knows what else is missing and unstable. Best to wipe and start cleanly after making a backup.
Also, I wouldn't try to fix anything - trying to make a new admin account could lose you even more data. Shut down that Mac and see about your options for making a backup to another computer or at least get a quote from someone that has the skills to help you back up your Mac.
The first skill to master if you want to try this is booting to target disk mode:
In your case, target disk works when your OS isn't able to give you admin rights. You can skip that if you have a good backup and just erase install your Mac.