How to mark a GPT Partition bootable under Linux

Question

• How to boot from a GPT Partition?
• Is it like the MBR way that needs a partition that has the bootable flag on?
• How to mark a GPT Partition bootable under Linux?

Answer 1

How to boot from a GPT Partition?

Booting a Linux installation involves multiple stages and software components, including firmware initialization, execution of a boot loader, loading and startup of a Linux kernel image, and execution of various startup scripts and daemons. For each of these stages and components there are different variations and approaches; for example, GRUB, LILO, SYSLINUX or Loadlin can be used as boot loaders, while the startup scripts can be either traditional init-style, or the system configuration can be performed through modern alternatives such as systemd or Upstart.

Another popular program to use to boot with is rEFInd a UEFI boot manager capable of launching EFISTUB kernels.

The EFI (Extensible Firmware Interface) system partition or ESP is a partition on a data storage device (usually a hard disk drive or solid-state drive) that is used by computers adhering to the Unified Extensible Firmware Interface (UEFI). When a computer is booted, UEFI firmware loads files stored on the ESP to start installed operating systems and various utilities.

An ESP contains the boot loaders or kernel images for all installed operating systems

Is it like the MBR way that needs a partition that has the bootable flag on?

The boot flag is from ancient times, where you would indicate an MBR partition record as bootable, so you could indicate where the boot loader resided. So to answer your question no you don't have to flag a boot partition bootable.

The globally unique identifier (GUID) for the EFI system partition in the GUID Partition Table (GPT) scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B, while its ID in the master boot record (MBR) partition-table scheme is 0xEF.

How to mark a GPT Partition bootable under Linux?

• In gdisk, you set the type code to EF00. (gdisk uses two-byte type codes that expand out to the real type codes on the disk; "EF00" is just a mnemonic for "C12A7328-F81F-11D2-BA4B-00A0C93EC93B".)
• In GParted or parted, you set the "boot flag." Note, however, that this works only on GPT disks; you cannot set the ESP type code on MBR disks with these programs. (This isn't normally a big deal, since EFI-based computers usually boot from GPT disks.)
• In recent versions of Linux fdisk, you set the partition type by its number (1 for "EFI System" on GPT disks or 0xEF on MBR disks) or by entering the full type code on GPT disks.