ubuntu Ubuntu Linux Crashed ... Understanding the Linux boot process, layers and typical scenarios is helpful in recovery from crash.
freebsd Converting FreeBSD from bios / mbr to UEFI / GPT Converting an existing bios/mbr installation to UEFI/GPT is a mechanistic exercise, requiring a spare disk and some expertise in gpart disk management tool. My example is virtual but the same basic process would also work with a physical machine.
iso Manipulating ISO Images for BIOS/UEFI Boot Support An example of how to repack a BIOS only ISO image for BIOS/UEFI dual boot
ubuntu Converting Ubuntu from bios to UEFI The simple way to convert Ubuntu VM from bios to UEFI boot