OSX Bootloader

Mounting the EFI Dir

sudo mkdir /Volumes/esp
sudo mount -t msdos /dev/disk0s1 /Volumes/esp

Blessing a boot loader

Disable System Integrity Protection.

Restart the computer, then while booting, hold down Command-R to boot into recovery mode.
Once booted, navigate to the “Utilities > Terminal” in the top menu bar.
Enter csrutil disable in the terminal window and hit the return key.

# first mount your efi partition
sudo mkdir /Volumes/esp
sudo mount -t msdos /dev/disk0s1 /Volumes/esp

# then bless the new boot loader
sudo bless --mount /Volumes/esp --setBoot --file /Volumes/esp/EFI/BOOT/bootx64.efi