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✏️ Editing: 445_guess_bootloader.sh

# Determine or guess the used bootloader if not specified by the user
# and save this information into /var/lib/rear/recovery/bootloader
local bootloader_file="$VAR_DIR/recovery/bootloader"

local sysconfig_bootloader
local block_device
local blockd
local disk_device
local bootloader_area_strings_file
local block_size
local known_bootloader

# When BOOTLOADER is specified use that:
if test "$BOOTLOADER" ; then
    LogPrint "Using specified bootloader '$BOOTLOADER'"
    echo "$BOOTLOADER" | tr '[a-z]' '[A-Z]' >$bootloader_file
    return
fi

# When a bootloader is specified in /etc/sysconfig/bootloader use that:
if test -f /etc/sysconfig/bootloader ; then
    # SUSE uses LOADER_TYPE, and others?
    # Getting values from sysconfig files is like sourcing shell scripts so that the last setting wins:
    sysconfig_bootloader=$( grep ^LOADER_TYPE /etc/sysconfig/bootloader | cut -d= -f2 | tail -n1 | sed -e 's/"//g' )
    if test "$sysconfig_bootloader" ; then
        LogPrint "Using sysconfig bootloader '$sysconfig_bootloader'"
        echo "$sysconfig_bootloader" | tr '[a-z]' '[A-Z]' >$bootloader_file
        return
    fi
fi

# On ARM, guess the dummy bootloader:
if [ "$ARCH" = "Linux-arm" ] ; then
    BOOTLOADER=ARM
    # Inform the user that we do nothing:
    LogPrint "Using guessed bootloader 'ARM'. Skipping bootloader backup, see default.conf"
    echo "$BOOTLOADER" >$bootloader_file
    return
fi

# Finally guess the used bootloader by inspecting the first bytes on all disks
# and use the first one that matches a known bootloader string:
for block_device in /sys/block/* ; do
    blockd=${block_device#/sys/block/}
    # Continue with the next block device when the current block device is not a disk that can be used for booting:
    [[ $blockd = hd* || $blockd = sd* || $blockd = cciss* || $blockd = vd* || $blockd = xvd* || $blockd = nvme* || $blockd = mmcblk* || $blockd = dasd*  ]] || continue
    disk_device=$( get_device_name $block_device )
    # Check if the disk contains a PPC PreP boot partition (ID=0x41):
    if file -s $disk_device | grep -q "ID=0x41" ; then
       LogPrint "Using guessed bootloader 'PPC' (found PPC PreP boot partition 'ID=0x41' on $disk_device)"
       echo "PPC" >$bootloader_file
       return
    fi
    # Get all strings in the first 512*4=2048 bytes on the disk:
    bootloader_area_strings_file="$TMP_DIR/bootloader_area_strings"
    block_size=$( get_block_size ${disk_device##*/} )
    dd if=$disk_device bs=$block_size count=4 | strings >$bootloader_area_strings_file
    # Examine the strings in the first bytes on the disk to guess the used bootloader,
    # see layout/save/default/450_check_bootloader_files.sh for the known bootloaders.
    # Test the more specific strings first because the first match wins.
    # Skip LUKS encrypted disks when guessing bootloader:
    if grep -q "LUKS" $bootloader_area_strings_file ; then
        LogPrint "Cannot autodetect bootloader on LUKS encrypted disk (found 'LUKS' in first bytes on $disk_device)"
        # Continue guessing the used bootloader by inspecting the first bytes on the next disk:
        continue
    fi
    # Check the default cases of known bootloaders.
    # IBM Z (s390) uses zipl boot loader for RHEL and Ubuntu
    # cf. https://github.com/rear/rear/issues/2137
    for known_bootloader in GRUB2 GRUB LILO ZIPL ; do
        if grep -q -i "$known_bootloader" $bootloader_area_strings_file ; then
            # If we find "GRUB" (which means GRUB Legacy)
            # do not unconditionally trust that because https://github.com/rear/rear/pull/589
            # reads (excerpt):
            #   Problems found:
            #   The ..._install_grub.sh checked for GRUB2 which is not part
            #   of the first 2048 bytes of a disk - only GRUB was present -
            #   thus the check for grub-probe/grub2-probe
            # and https://github.com/rear/rear/commit/079de45b3ad8edcf0e3df54ded53fe955abded3b
            # reads (excerpt):
            #    replace grub-install by grub-probe
            #    as grub-install also exist in legacy grub
            # so that if actually GRUB 2 is used, the string in the bootloader area
            # is "GRUB" so that another test is needed to detect if actually GRUB 2 is used.
            # When GRUB 2 is installed we assume GRUB 2 is used as boot loader.
            if [ "$known_bootloader" = "GRUB" ] && is_grub2_installed ; then
                known_bootloader=GRUB2
                LogPrint "GRUB found in first bytes on $disk_device and GRUB 2 is installed, using GRUB2 as a guessed bootloader for 'rear recover'"
            else
            LogPrint "Using guessed bootloader '$known_bootloader' (found in first bytes on $disk_device)"
            fi
            echo "$known_bootloader" >$bootloader_file
            return
        fi
    done
    # When no known bootloader matches the first bytes on the current disk
    # log all strings in the first bytes on the current disk
    # so that the user can see the results in the log file:
    Log "No known bootloader matches the first bytes on $disk_device"
    Log "Begin of strings in the first bytes on $disk_device"
    cat $bootloader_area_strings_file >&2
    Log "End of strings in the first bytes on $disk_device"
done

# No bootloader detected, but we are using UEFI - there is probably an EFI bootloader
if is_true $USING_UEFI_BOOTLOADER ; then
    if is_grub2_installed ; then
        echo "GRUB2-EFI" >$bootloader_file
    elif test -f /sbin/elilo ; then
        echo "ELILO" >$bootloader_file
    else
        # There is an EFI bootloader, we don't know which one exactly.
        # The value "EFI" is a bit redundant with USING_UEFI_BOOTLOADER=1,
        # which already indicates that there is an EFI bootloader. We use it as a placeholder
        # to not leave $bootloader_file empty.
        # Note that it is legal to have USING_UEFI_BOOTLOADER=1 and e.g. known_bootloader=GRUB2
        # (i.e. a non=EFI bootloader). This will happen in BIOS/UEFI hybrid boot scenarios.
        # known_bootloader=GRUB2 indicates that there is a BIOS bootloader and USING_UEFI_BOOTLOADER=1
        # indicates that there is also an EFI bootloader. Only the EFI one is being used at this
        # time, but both will need to be restored.
        echo "EFI" >$bootloader_file
    fi
    return 0
fi

# Error out when no bootloader was specified or could be autodetected:
Error "Cannot autodetect what is used as bootloader, see default.conf about 'BOOTLOADER'"

MR SKB