Last time I prepared the USB drive to boot from ISO. That’s great, but it’s no good if there are no ISOs to boot into.

First off, I set up Ubuntu in GRUB. Fortunately, this was pretty easy to do. Ubuntu supports booting from ISO using the iso-scan kernel parameter. Since Linux Mint is derived from Ubuntu, it also supports this parameter. The following lines in the GRUB2 config will enable booting from a Ubuntu/Linux Mint ISO.

menuentry "Ubuntu 9.10 32bit" {
    loopback loop /ubuntu-9.10-desktop-i386.iso
    linux (loop)/casper/vmlinuz boot=casper \
        iso-scan/filename=/ubuntu-9.10-desktop-i386.iso noeject noprompt --
    initrd (loop)/casper/initrd.lz
}

The loopback line loads the ISO in a way that GRUB can locate the kernel and initrd. The stuff about casper is something used for data persistence (so that the ISO remains read-only). I don’t have that enabled yet. This GRUB entry works similarly for Ubuntu (32- & 64-bit), Ubuntu Netbook Remix, and Linux Mint (32- & 64-bit).