- Boot the Mac into single user mode (holding down the Command+S keys during startup)
- Check the filesystem:
3. Mount the root drive as writable:
mount -uw /
4. Remove the hidden file /var/db/.applesteupdone:
5. Reboot the computer
You’ll now boot into the computer with the familiar Welcome screen. Create a NEW user, different than the ones that currently existed on the computer. It will be an admin user, and you’ll be able to change the passwords on the other accounts.