A script to help with diagnosing legacy BIOS boot issues on Macs

dumpvols.sh

#!/bin/bash
#
# Get Partition Info from all disks
#
# Written by joevt updated Dec 29. 2020
#  Patches marked "rgh" July, 2010, to dump information beyond the 
#   four bios partitions
#
#	sudo ./dumpvols.sh > dumpvols_result.txt 2>&1
#
# Based on johnsock's AHCI Master Boot Record Patch.
#
# This script is freely distributable.
#

if [ ! "$USER" = "root" ]; then
	echo WARNING: This script must be run as root.
	exit
fi

MBRHASHES=\
"Windows_XP=d88d4f2dbc2c662db7d7d60ebf9e3e00 "\
"Windows_Vista=12c9d7ff4914c88a7f9eadf9211b861b "\
"Windows_7=118eb70c44cb69284e5d8aa93096831e "\
"None_all_zeros=4ebc676ce4896613a3a9df6e2a1c77ae "\
""\
"MSDOS_or_FreeDOS_on_FreeDOS=93dd2ee87a995e36cbab0c2d5c2f041a "\
""\
"Windows_XP_On_BootCamp2_with_AHCI_patch=c3fb54174bc479899d4ef6e45308dc18 "\
"Windows_XP_On_BootCamp2=cb4dabdd862da0508083b05814e198b8 "\
"Windows_Vista_on_XP_with_AHCI_patch=4979e1b9d70738759280f6962c2ad298 "\
"Windows_7_on_XP=7db43c1425e9ff3077dd62b776a50419 "\
"Windows_7_with_AHCI_patch=a243d3475531b0f6f0d7199043c2eb5c "\
"Windows_7_on_XP_with_AHCI_patch=24977c27865adec9ac8298f1a8d214bf "\
""\
"Apple_Partition_Map_Block0_Driver_Descriptor_Map_390721968_blocks_and_Tiger_OS_9_drivers=087f35e49a39d52a46e3a94882869f51 "\
""


#All VBR hashes use all the bytes starting from offset 0x60. It may be better to use a different range for each type of VBR...

# GRUB2 hash was incorrectly named GRUB #rgh
# added GRUB hash from observation of kununtu 9.04 #rgh
# added Windows 8
VBRHASHES=\
"None_all_zeros=acf496fff71230daa6985a701f83ce49 "\
"NTFS_No_Loader=3be27456483746abb85cd614381dac5e "\
"NTFS_Windows_XP_NTLDR=dd1728a59343b9fa9458d80657f68771 "\
"NTFS_Windows_Vista_BOOTMGR=d1c278b56eeea9536d0eb5898fe6a0b5 "\
"NTFS_Windows_8_BOOTMGR=771df8b803f96296854316d3d5918812 "\
"GRUB_from_Ubuntu=332469fa146db809f58d6392e2e0bdce "\
"GRUB2_from_Ubuntu=9c249066e1eb9c842d8acdfe6d23a2e3 "\
"FAT32_FRDOS4.1=98050815221ee147066f99f806c23203 "\
"FAT32_FRDOS4.1_or_MSWIN4.1_BOOTMGR=aec608de8ac709d91e6f3340b643ab4d "\
"FAT32_NTFS_NTLDR=d9c3d66e975d2b3b122353951a598b32 "\
"FAT12_BSD_4.4_BOOTMGR=4cc92970d5a3350bc72d2b975e28b915 "\
"FAT16_Non_system_disk=2a3d0f51ad246f115aa7d37891788857 "\
"FAT32_Non_system_disk_or_EFI=34f2d1f3c3ecce5c00cae8f0b82c922b "\
"HFS_boot_block_0=28f5bc1563fbaedeb8dabbd4ef9eb4c2 "\
""

FindHash () {
	# $1: name of hashed contents
	# $2: list of known hashes
	# $3: the hash to search for
	DIDFIND=0
	for CURHASH in $2; do
		THEHASH=$(expr "$CURHASH" : '[^=]*=\(.*\)')
		THEOS=$(expr "$CURHASH" : '^\([^=]*\)=')
		if [ "$3" = "$THEHASH" ]; then
			DIDFIND=1
			break
		fi
	done
	echo ""
	if [ $DIDFIND = 1 ]; then
		echo "$1: $THEOS"
	else
		echo "$1: Unrecognized (hash=$3)"
	fi
}

disklist="$(diskutil list)"
echo "$disklist"
echo
diskutil apfs list

DRIVELIST=$(sed -n -E "/^[ ]*0: [ ]{0,25}([A-Za-z_]+)[ ]*\*[0-9.]+ [TGMK]B[ ]+(disk[0-9]+)$/s//\1_\2/p;/^[ ]*0: [ ]{0,26} .* \*[0-9.]+ [TGMK]B[ ]+(disk[0-9]+)$/s//whole_\1/p" <<< "$disklist")
for PARTDRIVE in $DRIVELIST;
do
	DRIVE=$(expr "$PARTDRIVE" : '.*_\([^_]*\)')
	PTYPE=$(expr "$PARTDRIVE" : '\(.*\)_[^_]*')
	echo "==============================================================================="

	diskutiloutput="$(sed -nE '/\/dev\/'$DRIVE' /,/^$/ p' <<< "${disklist}")"
	echo "$diskutiloutput"
	
	echo "---------------------------------------------"
	diskinfo="$(diskutil info $DRIVE)"
	echo "$diskinfo"
	echo
	BLOCKSIZE=$(sed -nE '/^ *Device Block Size: +([0-9]+).*/s//\1/p' <<< "$diskinfo")
	if [[ -z $BLOCKSIZE ]]; then
		BLOCKSIZE=512
	fi

	DEVLIST=$(echo "$diskutiloutput" | sed -n -E "/^.* (disk[0-9]+s[0-9]+)$/s//\1/p")
	for THEDEV in $DEVLIST; do
		echo "---------------------------------------------"
		diskutil info $THEDEV
	done

	if [ "$PTYPE" = "Apple_partition_scheme" ]; then
		pdisk -r -l "/dev/$DRIVE"
		pdisk -r -l -f "/dev/$DRIVE"

		# use the same bytes as MBR hash even though Block0 contents are totally different
		HASH=$(dd if="/dev/$DRIVE" bs=1 count=446 2> /dev/null | xxd -p -l 440 | md5)
		FindHash "Block0 contents" "$MBRHASHES" "$HASH"
		dd if="/dev/$DRIVE" bs=1 count=512 2> /dev/null | xxd -c 16
	elif [ "$PTYPE" = "GUID_partition_scheme" -o "$PTYPE" = "FDisk_partition_scheme" ]; then

		gptoutput="$(gpt -r show $DRIVE 2>&1)"
		gptoutput2="$(gpt -r show -l $DRIVE 2>&1)"
		fdiskoutput="$(fdisk /dev/r$DRIVE)"

		echo "$gptoutput"
		echo "$gptoutput2"
		echo "$fdiskoutput"

		HASH=$(dd if="/dev/$DRIVE" bs=1 count=446 2> /dev/null | xxd -p -l 440 | md5)
		FindHash "MBR contents" "$MBRHASHES" "$HASH"
		dd if="/dev/$DRIVE" bs=1 count=512 2> /dev/null | xxd -c 16

		if [ "$PTYPE" = "FDisk_partition_scheme" ]; then
			PARTLIST=$(echo "$fdiskoutput" | sed -n -E "/^[ \*]+([0-9])\: .*\[[ ]*([0-9]+) \-[ ]+([1-9][0-9]*)\].*$/s//\1_\2_\3/p")
			PARTTYPE="MBR"
		else
			HASH=$(dd if="/dev/$DRIVE" bs=1 skip=$((BLOCKSIZE + 96)) count=416 2> /dev/null | xxd -p -l 440 | md5)
			FindHash "GPT Header @ 1: GPT Header contents" "$VBRHASHES" "$HASH"
			dd if="/dev/$DRIVE" bs=1 skip=$BLOCKSIZE count=$BLOCKSIZE 2> /dev/null | xxd -c 16

			PARTLIST=$(echo "$gptoutput" | sed -n -E "/^[ ]+([0-9]+)[ ]+([0-9]+)[ ]+([0-9]+)[ ]+GPT part \-.*$/s//\3_\1_\2/p")
			PARTTYPE="GPT"
		fi

		for THEPART in $PARTLIST; do
			PNUM=$(expr "$THEPART" : '\([0-9]*\)_')
			PSTART=$(expr "$THEPART" : '[0-9]*_\([0-9]*\)_[0-9]*')
			PLENGTH=$(expr "$THEPART" : '[0-9]*_[0-9]*_\([0-9]*\)')

			HASH=$(dd if="/dev/$DRIVE" bs=1 skip=$((PSTART * BLOCKSIZE + 96)) count=416 2> /dev/null | xxd -p -l 440 | md5)
			FindHash "$PARTTYPE $PNUM @ $PSTART: VBR contents" "$VBRHASHES" "$HASH"
			dd if="/dev/$DRIVE" bs=1 skip=$((PSTART * BLOCKSIZE)) count=$BLOCKSIZE 2> /dev/null | xxd -c 16
		done
	elif [ "$PTYPE" = "whole" ]; then
		HASH=$(dd if="/dev/$DRIVE" bs=1 count=416 2> /dev/null | xxd -p -l 440 | md5)
		FindHash "0 @ 0: VBR contents" "$VBRHASHES" "$HASH"
		dd if="/dev/$DRIVE" bs=512 count=1 2> /dev/null | xxd -c 16
	else
		echo "Unknown partition scheme"
	fi
done
echo "==============================================================================="
ioreg -rw 0 -c IOMedia | sed -n -E "/^[ \|]*\+\-o (.*)  <class IOMedia[^a-zA-Z]/,/^[ \|]+ }$/p" | sed -n -E "/^[ \|]*\+\-o (.*)/s//\1/p;/^[ \|]* \| (.*)/s//\1/p;"
echo "==============================================================================="
bless --verbose --getboot
echo "==============================================================================="
bless --verbose --info
echo "==============================================================================="
ioreg -rw 0 -n AppleEFINVRAM | sed -n -E "/^[ \|]+[ ]+(\".*)$/s//\1/p;"
echo "==============================================================================="

• Download

cd ~/Downloads
curl -L https://gist.github.com/joevt/a99e3af71343d8242e0078ab4af39b6c/raw -o dumpvols.sh
xattr dumpvols.sh 2> /dev/null | grep com.apple.quarantine && xattr -d com.apple.quarantine dumpvols.sh
chmod +x dumpvols.sh

• Run

sudo ./dumpvols.sh > dumpvols_1.txt 2>&1

• Notes
  Run the command before and after making partition changes. Use a different file name each time. This way you can compare the files to see what changed and to make sure the changes are correct.

This script does not list boot files. Do that manually for each partition you think should be bootable. The boot code in a VBR (also known as PBR) should show what file it's looking to boot. For Windows 7 and later, it should be BOOTMGR. That file should exist in the root directory with a Boot folder containing a BCD folder containing a BCD file. The BCD file contains a menu of items to be bootable and boot options. Use EasyBCD.exe to edit the BCD of any partition. The files may be invisible in macOS - type Command-Shift-Period to show invisible files in the Finder.