An Hybrid UEFI GPT + BIOS GPT/MBR boot USB disk is a disk that works on both UEFI and BIOS PCs.
Requisites:
A working Linux installation with the following packages: grub2, grub2-efi, gdisk (on Debian Jessie: grub-pc-bin, grub-efi, grub-efi-amd64, gdisk) An USB drive Some Linux ISO.
Step 1: get the proper /dev
From now on we will use a root shell because almost all commands we will use require it.
root@debianvm:~# fdisk -l ............... Disk /dev/sdc: 14.9 GiB, 16005464064 bytes, 31260672 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x00000000 Device Boot Start End Sectors Size Id Type /dev/sdc1 2 31260671 31260670 14.9G af HFS / HFS+
then find the your USB Drive's dev (ie: mine was /dev/sdc and i will use it in the guide)