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2016-04-20-uefi_external_hd_boot.md

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Uefi external hd boot

Category: sysadmin Generated on 2016-04-20

source: https://askubuntu.com/questions/559007/is-it-still-possible-to-install-ubuntu-to-an-external-harddrive-with-uefi

EFI System Partitions = ESP

add ESP to existing MBR

  1. Install the grub-efi-amd64-bin package
  2. Shrink you partition to create a new ESP partition of 100-500MB
    It shouldn't matter where your ESP is located on the disk and shrinking your Ubuntu partition by a few megabytes from the end should be quick and safe. One caveat though, your ESP should be a primary partition and not be part of an extended partition or a logical volume, partition numbers from 1 to 4 are fine, numbers above indicate an extended partition on MBR partition tables. Choose FAT32 as filesystem and set the boot flag.
  3. mount ESP and root filesystem
mkdir -p /mnt/esp
mount {/dev/sdb1} /mnt/esp
mkdir -p /mnt/rootfs
mount {/dev/sdb2} /mnt/rootfs
  1. install grub
    grub-install --efi-directory /mnt/esp --boot-directory /mnt/rootfs/boot --target x86_64-efi --removable $device

Note that $device is the whole device e.g. /dev/sdb, not a partition.

The parameter --target x86_64-efi will ensure that UEFI images and modules will be installed to the given paths. --removable will install the UEFI image to the hardcoded path \EFI\BOOT\BOOT{arch}.EFI for removable media, instead of a distribution specific path. Your grub.cfg in /boot/grub/ should work with both boot methods.

add ESP to existing GPT

  1. Install the grub-efi-amd64-bin package.
  2. Create a partition with a FAT32 filesystem similar to the instructions above by resizing the root partition and set the boot flag.
  3. Mount the partitions and run the grub-install command from above that includes the --removable parameter.

This also works if you just want to boot your exisitng UEFI installation on another computer.