Restore MacOS over Ubuntu

Does trying to boot holding down OPTION-COMMAND-R or SHIFT-OPTION-COMMAND-R start up Internet Recovery Mode? If so you can use Disk Utility and wipe the partition and format the drive as Mac OS Extended (journaled) then close Disk Utility and select Reinstall OS X from the main Internet Recovery Menu.

If you erased the whole drive, then the local Recovery Partition is gone. If you never installed OSX 10.12.4+, then Internet Recovery Mode is not an option. If this is the case, then you will need another Mac to download an OSX installer and create a bootable OSX USB drive. If you don't have access to another Mac (or a friend), then you can see if Apple or an independent Apple Authorized Service Provider can assist you by making a bootable OSX USB installer for you.

You may be able to do a reinstall by starting up while holding the command and r keys down (having if necessaruy formatted the disk to Mac OS Extended (Journaled) as mentioined above: please see

How to reinstall macOS from macOS Recovery - Apple Support

It depends on whether your Ubuntu installation has done any damage to the recovery process. There are other startup commands given in that page, to install the original OS you Mac came with (if possible) or the highest OS your Mac can handle (which may or may not be El Capitan).

You are pretty much on your own there. You will have to somehow format the drive so that it formatted to Mac OS Extended (Journaled), once done you can begin installing Mac OS.

Good luck!

i had to chat with apple pepoel to help me they cant figure out but go to trimnail and buy the app logo and type date and make sure the date is right. And time is right