[Linux] Convert boot mode to UEFI

convert-to-efi.chroot.sh

#!/bin/bash
#
# Convert to EFI
#
# IMPORTANT NOTES:
#   * This script CAN ONLY BE running in a chrooted environment.
#   * This script will install shim, but still secure boot may fail.
#
# Tested for CentOS 7, but should have a similar process for all other
# Linux distros, at least for RHEL for its derivatives.
# 
# This script can be run on a BIOS booted environment as well, such as most of
# AWS EC2 x86_64 AMI. (Guess why I'm testing on BIOS environment.)
#
# This script assumes you've done the following things:
#   1. Creates GPT table on the destination disk, which contains:
#       * (Optional) BIOS Boot volulme (usually around 4M)
#       * EFI System volume (usually around 1G)
#       * Primary Linux volume (takes the rest of the space)
#      The layout should like this:
#           First Sector                    Last Sector
#           | BIOS | EFI   | Linux                    |
#   2. Mounted the disks as follow:
#       * <Old BIOS boot Linux volume> => /mnt/src
#       * <Primary Linux volume> => /mnt/dst
#       * <EFI System volume> => /mnt/dst/boot/efi (create this directory
#         if not exists)
#   3. Copy everything from source to destination with preserving
#      all attributes:
#       cp -R --preserve=all /mnt/src/* /mnt/dst/
#   4. Mount additional volumes before chroot:
#       * mount --type proc /proc /mnt/dst/proc
#       * mount --rbind /dev /mnt/dst/dev
#       * mount --rbind /sys /mnt/dst/sys
#       * mount --make-rslave /mnt/dst/dev
#       * mount --make-rslave /mnt/dst/sys
#   5. Chrooted into /mnt/dst:
#       sudo chroot /mnt/dst /bin/bash
#       

SYSTEM_DISK=/dev/vdc
EFI_SYSTEM_VOLUME=${SYSTEM_DISK}2
MAIN_SYSTEM_VOLUME=${SYSTEM_DISK}3

# Install required packages for EFI boot
yum install shim grub2-efi grub2-efi-modules efibootmgr

# Install BIOS-compatible bootloader
grub2-install $SYSTEM_DISK

# Install EFI bootloader
grub2-install --target x86_64-efi --efi-directory /boot/efi $SYSTEM_DISK

# Setup GRUB config
echo "GRUB_DISABLE_OS_PROBER=true" >> /etc/sysconfig/grub
grub2-mkconfig -o /boot/grub2/grub.cfg
# EFI cannot use 16-bit boot mode, forcefully change it to linuxefi and
# initrdefi.
sed -i -E 's/(linux|initrd)16/\1efi/' /boot/grub2/grub.cfg

pushd /etc
rm grub2-efi.cfg
ln -s ../boot/grub2/grub.cfg grub2-efi.cfg
popd

# Let GRUB find configuration file from main system volume
cat << EOF > /boot/efi/EFI/centos/grub.cfg
search --no-floppy --fs-uuid --set=root $(blkid -s UUID -o value $MAIN_SYSTEM_VOLUME)
set prefix=(\$root)/boot/grub2

export \$prefix
configfile \$prefix/grub.cfg
EOF

cp /etc/fstab /etc/fstab.backup
rm /etc/fstab

add_fstab_entry(){
    if [ -z "$1" ] || [ -z "$2" ]; then
        cat << EOF > &2
Usage: $0 DEVICE MOUNT_PATH [MOUNT_OPTION]

Add mount profile into /etc/fstab, where DEVICE will automatically
converted into UUID format.
EOF
        return 1
    fi
    MOUNT_OPTION=${3:-defaults}
    printf 'UUID=%-36s %-30s %-10s %-15s 0 0\n' \
        "$(blkid -s UUID -o value $1)" \
        "$2" \
        "$(blkid -s TYPE -o value $1)" \
        "$MOUNT_OPTION" | tee -a /etc/fstab
}

add_fstab_entry "$MAIN_SYSTEM_VOLUME" /
add_fstab_entry "$EFI_SYSTEM_VOLUME" /boot/efi

# Restore SELinux context
restorecon -R /