Installing custom ubuntu+grub on a secondary bootable drive

Question

I am using debootstrap to create a custom Xenial-based distro which can then be written to a secondary bootable drive from a host machine. (Target is an Intel NUC.) When I put the drive in the target PC and power on, the EFI recognizes the bootable drive but cannot boot it (it immediately returns to the EFI boot menu.)

So I don't believe I'm actually getting as far as grub launching. I'm guessing this is a grub install/config issue.

Relevant portion of my script:

local DISK=$1 # e.g. /dev/sdc
local EFI_PARTITION=${DISK}1
local ROOT_PARTITION=${DISK}2
local ROOT_MOUNT=$(mktemp -d)

# create partitions and format
parted -s --align=minimal $DISK \
       mklabel gpt \
       mkpart ESP fat32 0% 513MiB \
       mkpart primary ext4 513MiB 100% \
       set 1 boot on
partprobe $DISK
sleep 1
mkfs.fat -F32 $EFI_PARTITION
mkfs.ext4 $ROOT_PARTITION

# copy rootfs
mount $ROOT_PARTITION $ROOT_MOUNT
rsync -a $CHROOT_DIR/ $ROOT_MOUNT

# enter chroot and install grub
for dir in /dev /proc /sys /run; do
  mount --bind $dir $ROOT_MOUNT/$dir
done
mkdir $ROOT_MOUNT/boot/efi
mount $EFI_PARTITION $ROOT_MOUNT/boot/efi

chroot $ROOT_MOUNT <<EOF
/usr/sbin/grub-install --bootloader-id=ubuntu ${DISK}
/usr/sbin/grub-mkconfig -o /boot/grub/grub.cfg
EOF

# generate fstab and additional customizations

# sync, unmount eject

I do see the correct partition UUID in the resulting grub.cfg.

Here's my partition details:

$ sudo parted /dev/sdb print
Model: ASMT 2115 (scsi)
Disk /dev/sdb: 64.0GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name     Flags
 1      17.4kB  538MB   538MB   fat32        ESP      boot, esp
 2      538MB   64.0GB  63.5GB  ext4         primary

After I added shim-singed to my debootsrap includes, here's what I see in /boot/efi:

$ sudo tree efi
efi
└── EFI
    └── ubuntu
        ├── grub.cfg
        ├── grubx64.efi
        ├── MokManager.efi
        └── shimx64.efi

After renaming EFI/ubuntu to EFI/BOOT and shimx64.efi to bootx64.efi I can boot from the drive! However I get a grub prompt... Guessing I'm down to grub config issues now.

I've been using these docs as my primary sources:

• the Ubuntu Installation guide
• this great ArchLinux Grub doc
• GrubEFIReinstall on Debian wiki

To be clear, I'm attempting to install a linux kernel/rootfs/bootloader to a drive connected to a host machine. That bootable drive is then put into a target machine and booted. This is not a dual-boot scenario.

Do I need to do something with efibootmgr on the target?

Answer 1

I suspect the issue is one of boot loader naming. Under EFI, a computer can boot in any number of ways:

• From a hard disk -- In a normal OS installation, the boot loader resides on the hard disk's EFI System Partition (ESP), which is a FAT32 partition with a particular type code (C12A7328-F81F-11D2-BA4B-00A0C93EC93B; EF00 in gdisk; "boot flag" and "esp flag" set in parted, GParted, or related tools). The boot loader can be named anything, but is conventionally placed in a subdirectory of EFI named after the OS or boot loader. For Ubuntu, it's EFI/ubuntu/shimx64.efi, although this is actually a shim program that calls GRUB at EFI/ubuntu/grubx64.efi, and GRUB can be set to launch directly if Secure Boot is disabled. The computer knows which program to launch because that information is stored in NVRAM.
• From a removable disk -- On a removable disk, including an OS installer or anything you want to move from one computer to another (as in your case), the rules are similar to a hard disk installation; however, because the NVRAM cannot be relied upon to hold the boot loader information, the boot loader is stored using a standardized filename, which is EFI/BOOT/bootx64.efi for x86-64/AMD64/X64 computers. This is often called the fallback filename. You'd put Shim in this filename and keep GRUB named grubx64.efi, but in the EFI/BOOT directory.
• In miscellaneous other ways -- There are other boot methods, such as booting from a network or in BIOS/CSM/legacy mode. These aren't relevant to your question.

The Ubuntu installer is designed to install to a hard disk. If you want to install to a removable disk, you must either move/rename the boot loader files after the installation or install GRUB (or another boot loader) manually. You can do this by renaming EFI/ubuntu to EFI/BOOT and then renaming shimx64.efi within that directory to bootx64.efi, or by copying the files to achieve a similar effect. Alternatively, you can install another boot loader entirely, although this is likely to be a more tedious proposition, and it may create complications, particularly if you want to boot on computers with Secure Boot enabled.