$ sudo efibootmgr
BootCurrent: 0000
Timeout: 5 seconds
BootOrder: 0000,0082
Boot0000* ubuntu
Boot0080* Mac OS X
Boot0081* Mac OS X
Boot0082*
BootFFFF*

$ sudo efibootmgr -o 0000,0082

menuentry "Exit to Max OS X" {
  exit
}

sudo update-grub