However, only HFS+ partitions appear to be attached in a way that GRUB can see, but GParted's initrd cannot mount HFS+ (or even exFAT) partitions, saying hfsplus not found in p or exfat not found in p, respectively. I wanted to boot GParted-0.13.0-1 (kernel 3.2.0-3-486) from a USB stick on my MacBook Air 11' (late 2010) using the EFI bootloader which appears when holding down Option while turning on the laptop.
