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✏️ Editing: 940_grub2_rescue.sh

# 940_grub2_rescue.sh
# This file is part of Relax-and-Recover, licensed under the GNU General
# Public License. Refer to the included COPYING for full text of license.

# Add the rescue kernel and initrd to the local GRUB 2 bootloader.

# With EFI_STUB enabled there will be no Grub entry.
is_true "$EFI_STUB" && return 0

# Only do it when explicitly enabled:
is_true "$GRUB_RESCUE" || return 0

# Only run this script when GRUB 2 is there
# (grub-probe or grub2-probe only exist in GRUB 2)
# in particular do not run this script when GRUB Legacy is used
# (for GRUB Legacy output/default/940_grub_rescue.sh is run):
if [[ ! $( type -p grub-probe ) && ! $( type -p grub2-probe ) ]] ; then
    LogPrint "Skipping GRUB_RESCUE setup for GRUB 2 (no GRUB 2 found)."
    return
fi

# Now GRUB_RESCUE is explicitly wanted and this script is the right one to set it up.
local grub_rear_menu_entry_name="Relax-and-Recover"
LogPrint "Setting up GRUB_RESCUE: Adding $grub_rear_menu_entry_name rescue system to the local GRUB 2 configuration."
test "unrestricted" = "$GRUB_RESCUE_USER" && LogPrint "Anyone can boot that and replace the current system via 'rear recover'."
# Now error out whenever it cannot setup the GRUB_RESCUE functionality.

# We don't need to do grub(2)-probe all the time
# adding $grub_num to whatever grub binary should do the trick
# e.g. grub${grub_num}-mkimage
local grub_num=""
if [[ $( type -p grub2-probe ) ]]; then
    grub_num="2"
fi

# Ensure that kernel and initrd are there:
test -r "$KERNEL_FILE" || Error "Cannot setup GRUB_RESCUE: Cannot read kernel file '$KERNEL_FILE'."
local initrd_file=$TMP_DIR/$REAR_INITRD_FILENAME
test -r $initrd_file || Error "Cannot setup GRUB_RESCUE: Cannot read initrd '$initrd_file'."

# Some commonly needed values:
local boot_dir="/boot"
local boot_kernel_name="rear-kernel"
local boot_initrd_name="rear-$REAR_INITRD_FILENAME"
local boot_kernel_file="$boot_dir/$boot_kernel_name"
local boot_initrd_file="$boot_dir/$boot_initrd_name"
local grub_config_dir="$boot_dir/grub${grub_num}"

# Esure there is sufficient disk space available in /boot for the local Relax-and-Recover rescue system:
function total_filesize {
    stat --format '%s' $@ 2>/dev/null | awk 'BEGIN { t=0 } { t+=$1 } END { print t }'
}
# Free space in /boot:
local free_space=$( df -Pkl $boot_dir | awk 'END { print $4 * 1024 }' )
# Used space by an already existing Relax-and-Recover rescue system in /boot:
local already_used_space=$( total_filesize $boot_kernel_file $boot_initrd_file )
# Available space is the free space plus what an already existing Relax-and-Recover rescue system uses
# because an already existing Relax-and-Recover rescue system would be overwritten:
local available_space=$(( free_space + already_used_space ))
# Required space for the new Relax-and-Recover rescue system:
local required_space=$( total_filesize $KERNEL_FILE $initrd_file )
if (( available_space < required_space )) ; then
    required_MiB=$(( required_space / 1024 / 1024 ))
    available_MiB=$(( available_space / 1024 / 1024 ))
    Error "Cannot setup GRUB_RESCUE: Not enough disk space in $boot_dir for $grub_rear_menu_entry_name rescue system. Required: $required_MiB MiB. Available: $available_MiB MiB."
fi

# TODO: @gozora this is quite long comment, maybe it could me moved to documentation?
#
# UEFI "Relax-and-Recover" boot entry motivation:
#
# If UEFI boot is in use, we will not modify grub.cfg, but setup "Relax-and-Recover" entry in UEFI boot menu instead.
# This looks to be simplest and safest approach since finding out what mechanisms were used to boot OS in UEFI mode,
# looks to be near to impossible.
# One could argue that efibootmgr/efivars can tell you, however this entry is not mandatory and OS could be booted
# using default values or startup.nsh.
# Once UEFI loads Grub2 hell breaks loose, as Grub2 can load whatever arbitrary configuration file anywhere on the system
# or configuration file can be even embedded in bootx64.efi (and friends) as file or memdisk.
# Unfortunately there seems to be no reliable way how to track this back.
#
# Once "Relax-and-Recover" entry in UEFI boot menu is created, user can choose to boot it from OS at next boot:
# # efibootmgr
#
# BootCurrent: 0001
# BootOrder: 0000,0001,0002,0003,0004
# Boot0000* EFI DVD/CDROM
# Boot0001* EFI Hard Drive
# Boot0002* EFI Hard Drive 1
# Boot0003* EFI Internal Shell
# Boot0004* Relax-and-Recover
#
# # /usr/sbin/efibootmgr --bootnext 4
# At next boot "Relax-and-Recover" rescue image from /boot will be loaded.
#
# To remove "Relax-and-Recover" UEFI boot entry:
#
# # efibootmgr -B -b 4
#
# "Relax-and-Recover" entry can be of course selected during POST boot as well.

if ! is_true $USING_UEFI_BOOTLOADER ; then
    # Ensure a GRUB 2 configuration file is found:
    local grub_conf=$( readlink -f $grub_config_dir/grub.cfg )
    test -w "$grub_conf" || Error "Cannot setup GRUB_RESCUE: GRUB 2 configuration '$grub_conf' cannot be modified."

# Report no longer supported GRUB 2 superuser setup if GRUB_SUPERUSER is non-empty
    # (be prepared for 'set -u' by specifying an empty fallback value if GRUB_SUPERUSER is not set):
    test ${GRUB_SUPERUSER:-} && LogPrint "Skipping GRUB 2 superuser setup: GRUB_SUPERUSER is no longer supported (see default.conf)."
    # Report no longer supported GRUB 2 password setup if GRUB_RESCUE_PASSWORD is non-empty
    # (be prepared for 'set -u' by specifying an empty fallback value if GRUB_RESCUE_PASSWORD is not set):
    test ${GRUB_RESCUE_PASSWORD:-} && LogPrint "Skipping GRUB 2 password setup: GRUB_RESCUE_PASSWORD is no longer supported (see default.conf)."
    # It is no error when GRUB_SUPERUSER and/or GRUB_RESCUE_PASSWORD are non-empty
    # because it should work reasonably backward compatible, see default.conf

# A simple check if a GRUB_RESCUE_USER exists in the usual GRUB 2 users file /etc/grub.d/01_users
    # but this check is unreliable because the GRUB 2 users filename could be anything else
    # so that it only notifies without interpretation and does not error out if the check fails.
    # On the other hand when /etc/grub.d/01_users exists then we might even assume that
    # this one is the only GRUB 2 users file and error out if GRUB_RESCUE_USER is not therein?
    local supposed_grub_users_file="/etc/grub.d/01_users"
    if test -r $supposed_grub_users_file -a "$GRUB_RESCUE_USER" -a "unrestricted" != "$GRUB_RESCUE_USER" ; then
        grep -q "$GRUB_RESCUE_USER" $supposed_grub_users_file || LogPrint "GRUB_RESCUE_USER '$GRUB_RESCUE_USER' not found in $supposed_grub_users_file - is that okay?"
    fi
fi

# Finding UUID of filesystem containing boot_dir (i.e. /boot)
grub_boot_uuid=$( df $boot_dir | awk 'END {print $1}' | xargs blkid -s UUID -o value )

# Stop if grub_boot_uuid is not a valid UUID
blkid -U $grub_boot_uuid > /dev/null 2>&1 || Error "$grub_boot_uuid is not a valid UUID"

# Creating Relax-and-Recover GRUB 2 menu entry:
local grub_rear_menu_entry_file="/etc/grub.d/45_rear"
local grub_boot_dir=$boot_dir
if mountpoint -q $boot_dir ; then
    # When /boot is a mountpoint
    # (i.e. a filesystem on a partition /dev/sdaN is mounted at /boot)
    # then GRUB uses the filesystem on /dev/sdaN directly
    # and in that filesystem there is no such thing as /boot
    # so that for GRUB the files are in the root of that filesystem:
    grub_boot_dir=""
fi

# Refer to: UEFI "Relax-and-Recover" boot entry motivation, near to beginning of this file ...
if is_true $USING_UEFI_BOOTLOADER ; then
    # SLES12 SP1 throw kernel panic if root= variable was not set
    # probably a bug, as I was able to boot with value set to root=anything
    root_uuid=$(get_root_disk_UUID)

# Create configuration file for "Relax-and-Recover" UEFI boot entry.
    # This file will not interact with existing Grub2 configuration in any way.
    (   echo "set btrfs_relative_path=y"
        echo "insmod efi_gop"
        echo "insmod efi_uga"
        echo "insmod video_bochs"
        echo "insmod video_cirrus"
        echo "insmod all_video"
        echo ""
        echo "set gfxpayload=keep"
        echo ""
        echo "menuentry '$grub_rear_menu_entry_name' --class os {"
        echo "          search --no-floppy --fs-uuid --set=root $grub_boot_uuid"
        echo "          echo 'Loading kernel $boot_kernel_file ...'"
        echo "          linux $grub_boot_dir/$boot_kernel_name root=UUID=$root_uuid $KERNEL_CMDLINE"
        echo "          echo 'Loading initrd $boot_initrd_file (may take a while) ...'"
        echo "          initrd $grub_boot_dir/$boot_initrd_name"
        echo "}"
        echo ""
        echo "menuentry 'Boot original system' {"
        echo "          search --fs-uuid --no-floppy --set=esp $esp_disk_uuid"
        echo "          chainloader (\$esp)$esp_relative_bootloader"
        echo "}"
    ) > $grub_config_dir/rear.cfg

# Create rear.efi at UEFI default boot directory location.
    build_bootx86_efi $boot_dir/efi/EFI/BOOT/rear.efi $grub_config_dir/rear.cfg "$boot_dir" "$UEFI_BOOTLOADER"

# If UEFI boot entry for "Relax-and-Recover" does not exist, create it.
    # This will also add "Relax-and-Recover" to boot order because if UEFI entry is not listed in BootOrder,
    # it is not visible in UEFI boot menu.
    if [[ $(efibootmgr | grep -cw $grub_rear_menu_entry_name) -eq 0 ]]; then
        # This part might not go that well with drivers like HPEs cciss...
        # However UEFI booting is present since Gen8 (AFAIK), and cciss drivers were replaced by hpsa long time ago,
        # so it looks like impossible configuration, lets wait ...
        efi_disk_part=$(grep -w /boot/efi /proc/mounts | awk '{print $1}')
        efi_disk=$(echo $efi_disk_part | sed -e 's/[0-9]//g')
        efi_part=$(echo $efi_disk_part | sed -e 's/[^0-9]//g')

# Save current BootOrder, as during `efibootmgr -c ...' phase (creating of "Relax-and-Recover" UEFI boot entry),
        # newly created entry will be set as primary, which is not something we don't really want
        efi_boot_order=$(efibootmgr | grep "BootOrder" | cut -d ":" -f2)
        efibootmgr -c -d $efi_disk -p $efi_part -L "$grub_rear_menu_entry_name" -l "\EFI\BOOT\rear.efi" > /dev/null 2>&1
        rear_boot_id=$(efibootmgr | grep -w $grub_rear_menu_entry_name | cut -d " " -f1 | sed -e 's/[^0-9]//g')

# Set "Relax-and-Recover" as last entry in UEFI boot menu.
        efibootmgr -o ${efi_boot_order},${rear_boot_id} > /dev/null 2>&1
    fi
else
    # Create a GRUB 2 menu config file:
      ( echo "#!/bin/bash"
        echo "cat << EOF"
      ) > $grub_rear_menu_entry_file
    if test "$GRUB_RESCUE_USER" ; then
        if test "unrestricted" = "$GRUB_RESCUE_USER" ; then
            echo "menuentry '$grub_rear_menu_entry_name' --class os --unrestricted {" >> $grub_rear_menu_entry_file
        else
            echo "menuentry '$grub_rear_menu_entry_name' --class os --users $GRUB_RESCUE_USER {" >> $grub_rear_menu_entry_file
        fi
    else
        echo "menuentry '$grub_rear_menu_entry_name' --class os {" >> $grub_rear_menu_entry_file
    fi
      ( echo "          search --no-floppy --fs-uuid --set=root $grub_boot_uuid"
        echo "          echo 'Loading kernel $boot_kernel_file ...'"
        echo "          linux $grub_boot_dir/$boot_kernel_name $KERNEL_CMDLINE"
        echo "          echo 'Loading initrd $boot_initrd_file (may take a while) ...'"
        echo "          initrd $grub_boot_dir/$boot_initrd_name"
        echo "}"
        echo "EOF"
      ) >> $grub_rear_menu_entry_file
    chmod 755 $grub_rear_menu_entry_file

# Generate a GRUB 2 configuration file:
    local generated_grub_conf="$TMP_DIR/grub.cfg"
    if [[ $( type -f grub2-mkconfig ) ]] ; then
        grub2-mkconfig -o $generated_grub_conf || Error "Failed to generate GRUB 2 configuration file (using grub2-mkconfig)."
    else
        grub-mkconfig -o $generated_grub_conf || Error "Failed to generate GRUB 2 configuration file (using grub-mkconfig)."
    fi
    test -s $generated_grub_conf || BugError "Generated empty GRUB 2 configuration file '$generated_grub_conf'."

# Modifying local GRUB 2 configuration if it was actually changed:
    if ! diff -u $grub_conf $generated_grub_conf >&2 ; then
        LogPrint "Modifying local GRUB 2 configuration."
        cp -af $v $grub_conf $grub_conf.old >&2
        cat $generated_grub_conf >$grub_conf
    fi
fi

# Provide the kernel as boot_kernel_file (i.e. /boot/rear-kernel):
if [[ $( stat -L -c '%d' $KERNEL_FILE ) == $( stat -L -c '%d' $boot_dir/ ) ]] ; then
    # Hardlink file, if possible:
    cp -pLlf $v $KERNEL_FILE $boot_kernel_file || BugError "Failed to hardlink '$KERNEL_FILE' to '$boot_kernel_file'."
elif [[ $( stat -L -c '%s %Y' $KERNEL_FILE ) == $( stat -L -c '%s %Y' $boot_kernel_file ) ]] ; then
    # If an already existing boot_kernel_file has exact same size and modification time
    # as the current KERNEL_FILE, assume both are the same and do nothing:
    :
else
    # In all other cases, replace boot_kernel_file with the current KERNEL_FILE:
    cp -pLf $v $KERNEL_FILE $boot_kernel_file || BugError "Failed to copy '$KERNEL_FILE' to '$boot_kernel_file'."
fi

# Provide the ReaR recovery system in initrd_file (i.e. TMP_DIR/initrd.cgz or TMP_DIR/initrd.xz)
# as boot_initrd_file (i.e. /boot/rear-initrd.cgz or /boot/rear-initrd.xz)
# (regarding '.cgz' versus '.xz' see https://github.com/rear/rear/issues/1142)
cp -af $v $initrd_file $boot_initrd_file || BugError "Failed to copy '$initrd_file' to '$boot_initrd_file'."

LogPrint "Finished GRUB_RESCUE setup: Added '$grub_rear_menu_entry_name' GRUB 2 menu entry."

MR SKB