Easy way of adding (MBR) Ubuntu option to (UEFI) Clover boot menu?

[asiga]

I think I didn't explain it well. Windows 10 and Ubuntu are in a secondary HDD. Windows 10 was installed first and it chose non-UEFI, non-GUID. Then Ubuntu was installed on the same drive. The primary disk is GUID, and it's only for OSX.

Clover found Windows, but not Ubuntu, but both of them are in a legacy partitioned drive.

 

[asiga]

I've finally arrived to a solution which, although not "perfect", is satisfactory for me: It turns out that GRUB was still at the MBR of the secondary drive, but I wasn't seeing it because the Clover Windows entry ignored it and booted Windows directly. But if I boot the secondary drive from the BIOS boot menu, then GRUB does appear.

So, I can boot in all the three OSs now, and they work fine, although the workflow is a bit non-standard:

For booting OS X: Plug the computer and let it go (Clover appears, the default option is OS X, just boots it).
For booting Windows: Plug the computer, press F12 for the BIOS boot menu, choose secondary drive, and from GRUB you go.
For booting Ubuntu: The same as for Windows, but with the proper GRUB entry.

So, for the moment I consider this closed and working --because I've a lot of things to do in OS X and the goal in my life isn't achieving a pristine ideal boot menu