mbr bootbug 222126 supporting data

[pxwpxw]

You dont want to read this, and don't try it.

this is a copy of my attachment to
https://bugs.edge.launchpad.net/ubuntu/+source/ubiquity/+bug/222126/
some destructive tests on intel mac MBR partiton data.
Here for any discussion arising.


MacBook2.1 80GB HD. Ubunu 704 and 810 parted comparison.
Fri Nov 14 01:42:47 EST 2008

1. The sda sector0 and MBR was wiped to 00*55aa (msdos MBR disk signature).
MBR=4x16byte partition entries above 446 bytes.

# dd if=/dev/zero of=/dev/sda bs=510 count=1
# hexdump -Cn512 /dev/sda
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200

Then using 704 live cd
# parted /dev/sda toggle 1 boot
done twice, no net no effect on gpt flag, but causing write to the disk MBR.

2. The MBR as parted on 704 left it.

00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fe |................|
000001c0 ff ff ee fe ff ff 01 00 00 00 27 40 06 00 80 fe |..........'@....|
000001d0 ff ff af fe ff ff 28 40 06 00 30 a1 7e 02 00 fe |......(@..0.~...|
000001e0 ff ff af fe ff ff 58 e1 88 02 08 20 ae 00 00 fe |......X.... ....|
000001f0 ff ff 83 fe ff ff 60 01 37 03 de 0e e9 02 55 aa |......`.7.....U.|
00000200

root@wdc:/home/pxw# gptsync /dev/sda

Current GPT partition table:
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 42262871 Mac OS X HFS+
3 42525016 53936479 Mac OS X HFS+
4 53936480 102764605 Basic Data
5 102764606 106670856 Linux Swap
(free space remaining)
Current MBR partition table:
# A Start LBA End LBA Type
1 1 409639 ee EFI Protective
2 * 409640 42262871 af Mac OS X HFS+
3 42525016 53936479 af Mac OS X HFS+
4 53936480 102764605 83 Linux

Status: Tables are synchronized, no need to sync.

root@wdc:/home/pxw#

Can boot using MBR without gptsync (boot sector code below MBR appeared later).
=====================

2. Wipe the MBR again to check 810 parted (from xububtu810 on external disk)

root@wdc:/home/pxw# dd if=/dev/zero of=/dev/sda bs=510 count=1
1+0 records in
1+0 records out
510 bytes (510 B) copied, 0.000584095 s, 873 kB/s
root@wdc:/home/pxw# hexdump -Cn512 /dev/sda
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200

root@wdc:/home/pxw# gptsync /dev/sda

Current GPT partition table:
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 42262871 Mac OS X HFS+
3 42525016 53936479 Mac OS X HFS+
4 53936480 102764605 Basic Data
5 102764606 106670856 Linux Swap

Current MBR partition table:
No partitions defined

Status: MBR table must be updated.

Proposed new MBR partition table:
# A Start LBA End LBA Type
1 1 409639 ee EFI Protective
2 409640 42262871 af Mac OS X HFS+
3 42525016 53936479 af Mac OS X HFS+
4 * 53936480 102764605 83 Linux

May I update the MBR as printed above? [y/N] n
No

//just checking its valid for gptsync, but leaved empty.

root@wdc:/home/pxw# parted

toggle 1

//810 parted complained, but offered choice of gpt disk, and then allowed the toggle operaation.
Flag to Invert? boot/hidden/raid/lvm/hp-service/msftres/bios_grub? boot

Information: You may need to update /etc/fstab.

root@wdc:/home/pxw# parted /dev/sda p

Model: ATA TOSHIBA MK8034GS (scsi)
Disk /dev/sda: 80.0GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number Start End Size File system Name Flags
1 20.5kB 210MB 210MB fat32 EFI System Partition msftres
2 210MB 21.6GB 21.4GB hfs+ Apple_HFS_Untitled_1
3 21.8GB 27.6GB 5843MB hfs+ Apple_HFS_Untitled_2
4 27.6GB 52.6GB 25.0GB ext3 root1
5 52.6GB 54.6GB 2000MB linux-swap

toggle back to boot on

root@wdc:/home/pxw# parted /dev/sda toggle 1 boot p
Model: ATA TOSHIBA MK8034GS (scsi)
Disk /dev/sda: 80.0GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number Start End Size File system Name Flags
1 20.5kB 210MB 210MB fat32 EFI System Partition boot
2 210MB 21.6GB 21.4GB hfs+ Apple_HFS_Untitled_1
3 21.8GB 27.6GB 5843MB hfs+ Apple_HFS_Untitled_2
4 27.6GB 52.6GB 25.0GB ext3 root1
5 52.6GB 54.6GB 2000MB linux-swap

Information: You may need to update /etc/fstab.

root@wdc:/home/pxw#
//that has reset the sector0 mbr to one partition, full disk size, valid for gptsync.

root@wdc:/home/pxw# hexdump -Cn512 /dev/sda
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001c0 01 00 ee fe ff ff 01 00 00 00 af f8 50 09 00 00 |............P...|
000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200
root@wdc:/home/pxw#


root@wdc:/home/pxw# gptsync /dev/sda

Current GPT partition table:
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 42262871 Mac OS X HFS+
3 42525016 53936479 Mac OS X HFS+
4 53936480 102764605 Basic Data
5 102764606 106670856 Linux Swap

Current MBR partition table:
# A Start LBA End LBA Type
1 1 156301487 ee EFI Protective

Status: MBR table must be updated.

Proposed new MBR partition table:
# A Start LBA End LBA Type
1 1 409639 ee EFI Protective
2 409640 42262871 af Mac OS X HFS+
3 42525016 53936479 af Mac OS X HFS+
4 * 53936480 102764605 83 Linux

May I update the MBR as printed above? [y/N] y
Yes

Writing new MBR...
MBR updated successfully!

root@wdc:/home/pxw#
root@wdc:/home/pxw# hexdump -Cn512 /dev/sda

00000000 fa 31 c0 8e d8 8e d0 bc 00 7c 89 e6 06 57 52 8e |.1.......|...WR.|
00000010 c0 fb fc bf 00 06 b9 00 01 f3 a5 ea 20 06 00 00 |............ ...|
00000020 52 b8 00 41 bb aa 55 31 c9 30 f6 f9 cd 13 72 13 |R..A..U1.0....r.|
00000030 81 fb 55 aa 75 0d d1 e9 73 09 66 c7 06 8f 06 b4 |..U.u...s.f.....|
00000040 42 eb 15 5a b4 08 cd 13 83 e1 3f 51 0f b6 c6 40 |B..Z......?Q...@|
00000050 f7 e1 52 50 66 31 c0 66 99 e8 67 00 e8 24 01 4d |..RPf1.f..g..$.M|
00000060 69 73 73 69 6e 67 20 6f 70 65 72 61 74 69 6e 67 |issing operating|
00000070 20 73 79 73 74 65 6d 2e 0d 0a 00 66 60 66 31 d2 | system....f`f1.|
00000080 bb 00 7c 66 52 66 50 06 53 6a 01 6a 10 89 e6 66 |..|fRfP.Sj.j...f|
00000090 f7 36 f4 7b c0 e4 06 88 e1 88 c5 92 f6 36 f8 7b |.6.{.........6.{|
000000a0 88 c6 08 e1 41 b8 01 02 8a 16 fa 7b cd 13 83 c4 |....A......{....|
000000b0 10 66 61 c3 e8 c4 ff be be 7d bf be 07 b9 20 00 |.fa......}.... .|
000000c0 f3 a5 c3 66 60 89 e5 bb be 07 b9 04 00 31 c0 53 |...f`........1.S|
000000d0 51 f6 07 80 74 03 40 89 de 83 c3 10 e2 f3 48 74 |Q...t.@.......Ht|
000000e0 5c 79 39 59 5b 8a 47 04 3c 0f 74 06 24 7f 3c 05 |\y9Y[.G.<.t.$.<.|
000000f0 75 22 66 8b 47 08 66 8b 56 14 66 01 d0 66 21 d2 |u"f.G.f.V.f..f!.|
00000100 75 03 66 89 c2 e8 ac ff 72 03 e8 b6 ff 66 8b 46 |u.f.....r....f.F|
00000110 1c e8 a0 ff 83 c3 10 e2 cc 66 61 c3 e8 64 00 4d |.........fa..d.M|
00000120 75 6c 74 69 70 6c 65 20 61 63 74 69 76 65 20 70 |ultiple active p|
00000130 61 72 74 69 74 69 6f 6e 73 2e 0d 0a 00 66 8b 44 |artitions....f.D|
00000140 08 66 03 46 1c 66 89 44 08 e8 2f ff 72 13 81 3e |.f.F.f.D../.r..>|
00000150 fe 7d 55 aa 0f 85 04 ff bc fa 7b 5a 5f 07 fa ff |.}U.......{Z_...|
00000160 e4 e8 1f 00 4f 70 65 72 61 74 69 6e 67 20 73 79 |....Operating sy|
00000170 73 74 65 6d 20 6c 6f 61 64 20 65 72 72 6f 72 2e |stem load error.|
00000180 0d 0a 00 5e ac 20 c0 74 0c b4 0e 8a 3e 62 04 b3 |...^. .t....>b..|
00000190 07 cd 10 eb ef cd 18 f4 eb fd 00 00 00 00 00 00 |................|
000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fe |................|
000001c0 ff ff ee fe ff ff 01 00 00 00 27 40 06 00 00 fe |..........'@....|
000001d0 ff ff af fe ff ff 28 40 06 00 30 a1 7e 02 00 fe |......(@..0.~...|
000001e0 ff ff af fe ff ff 58 e1 88 02 08 20 ae 00 80 fe |......X.... ....|
000001f0 ff ff 83 fe ff ff 60 01 37 03 de 0e e9 02 55 aa |......`.7.....U.|
00000200
======

The MBR boot flag at 0x1ee on partition #4 is not shown by parted; appears irrelevant here.

root@wdc:/home/pxw# parted /dev/sda p free
Model: ATA TOSHIBA MK8034GS (scsi)
Disk /dev/sda: 80.0GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number Start End Size File system Name Flags
17.4kB 20.5kB 3072B Free Space
1 20.5kB 210MB 210MB fat32 EFI System Partition boot
2 210MB 21.6GB 21.4GB hfs+ Apple_HFS_Untitled_1
21.6GB 21.8GB 134MB Free Space
3 21.8GB 27.6GB 5843MB hfs+ Apple_HFS_Untitled_2
4 27.6GB 52.6GB 25.0GB ext3 root1
5 52.6GB 54.6GB 2000MB linux-swap
54.6GB 80.0GB 25.4GB Free Space


gptsync now reports " Status: Tables are synchronized, no need to sync."

Ready to boot MBR loaders.
=======

[cyberdork33]

thanks for the help man. That has been a long-standing bug,

[pxwpxw]

Here is part 2 -

Two more tests were done to reproduce the flashing [?] folder, with the unbootable hard disk.

On a MacBook2,1 the only other way I could reproduce it was by using fdisk and (ignoring warnings) to delete the single full disk partition it shows for the gpt default entry. This zeroed the MBR. I dont think it is a parted bug.
I have rechecked all this, but it has all been done on a MacBook2,1. I dont know if there are any different issues for other macs e.g. with drive differences.

Warning -
Do not do this test unless you understand the risk and can recover.

1. I zeroed out the whole first sector of the disk with dd to give this hexdump


root@wdc:~/devsda-zap00# hexdump -Cn512 /dev/sda

00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000200


Restart goes to [?] flash folder after ~30 seconds, and nothing will boot from the HD.

Then checked with gptsync running from the refit CD (which still boots).


root@wdc:~/zapdevsda-00# gptsync /dev/sda

Current GPT partition table:
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 42262871 Mac OS X HFS+
3 42525016 53936479 Mac OS X HFS+
4 53936480 102764605 Basic Data
5 102764606 106670856 Linux Swap

Current MBR partition table:
No MBR partition table present!



So the GPT table above the first sector is ok, but gptsynce is no help here.
But it can easily be fixed, read on.

2. restore the 55aa msdos signature bytes 511, 512.
(note 1).


root@wdc:~/zapdevsda-00# hexdump -Cn512 /dev/sda
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200


This gets the same [?] folder, nothing boots, but gptsync from the CD now recognises MBR present, and can sync, restoring full MBR and all fixed
.

root@wdc:~/zapdevsda-00# gptsync /dev/sda

Current GPT partition table:
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 42262871 Mac OS X HFS+
3 42525016 53936479 Mac OS X HFS+
4 53936480 102764605 Basic Data
5 102764606 106670856 Linux Swap

Current MBR partition table:
No partitions defined

Status: MBR table must be updated.

Proposed new MBR partition table:
# A Start LBA End LBA Type
1 1 409639 ee EFI Protective
2 409640 42262871 af Mac OS X HFS+
3 42525016 53936479 af Mac OS X HFS+
4 * 53936480 102764605 83 Linux

May I update the MBR as printed above? [y/N] y
Yes

Writing new MBR...
MBR updated successfully!

(hexdump note2)

All fixed if you have grub on another partition, not the MBR.

3. HAZARDOUS - I also found that ubuntu 810 parted can be made to regenerate a valid gpt sector1 (ie.e bootable and acceptable to gptsync) ) by toggling the partition 1 boot flag off and on. Parted complains at first and has to be told that it has a GPT table. If you make a mistake here and tell it that it is an MBR disk it can convert to msdos partitioning and lose everything.

------------------
Note 1. restoring the hex 55aa. (echo uses octal).


$ dd if=/dev/zero of=testsector bs=512 count=1
$ echo -en "\0125\0252" > hex55aa && dd if=hex55aa of=testsector seek=1 bs=510
pxw@g5:~/test$ hexdump -C testsector
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200


Note 2. restored MBR and bootcode
MacBook2,1 80GB GPT/MBR disk.

root@wdc:~/zapdevsda-00# hexdump -Cn512 /dev/sda
00000000 fa 31 c0 8e d8 8e d0 bc 00 7c 89 e6 06 57 52 8e |.1.......|...WR.|
00000010 c0 fb fc bf 00 06 b9 00 01 f3 a5 ea 20 06 00 00 |............ ...|
00000020 52 b8 00 41 bb aa 55 31 c9 30 f6 f9 cd 13 72 13 |R..A..U1.0....r.|
00000030 81 fb 55 aa 75 0d d1 e9 73 09 66 c7 06 8f 06 b4 |..U.u...s.f.....|
00000040 42 eb 15 5a b4 08 cd 13 83 e1 3f 51 0f b6 c6 40 |B..Z......?Q...@|
00000050 f7 e1 52 50 66 31 c0 66 99 e8 67 00 e8 24 01 4d |..RPf1.f..g..$.M|
00000060 69 73 73 69 6e 67 20 6f 70 65 72 61 74 69 6e 67 |issing operating|
00000070 20 73 79 73 74 65 6d 2e 0d 0a 00 66 60 66 31 d2 | system....f`f1.|
00000080 bb 00 7c 66 52 66 50 06 53 6a 01 6a 10 89 e6 66 |..|fRfP.Sj.j...f|
00000090 f7 36 f4 7b c0 e4 06 88 e1 88 c5 92 f6 36 f8 7b |.6.{.........6.{|
000000a0 88 c6 08 e1 41 b8 01 02 8a 16 fa 7b cd 13 83 c4 |....A......{....|
000000b0 10 66 61 c3 e8 c4 ff be be 7d bf be 07 b9 20 00 |.fa......}.... .|
000000c0 f3 a5 c3 66 60 89 e5 bb be 07 b9 04 00 31 c0 53 |...f`........1.S|
000000d0 51 f6 07 80 74 03 40 89 de 83 c3 10 e2 f3 48 74 |Q...t.@.......Ht|
000000e0 5c 79 39 59 5b 8a 47 04 3c 0f 74 06 24 7f 3c 05 |\y9Y[.G.<.t.$.<.|
000000f0 75 22 66 8b 47 08 66 8b 56 14 66 01 d0 66 21 d2 |u"f.G.f.V.f..f!.|
00000100 75 03 66 89 c2 e8 ac ff 72 03 e8 b6 ff 66 8b 46 |u.f.....r....f.F|
00000110 1c e8 a0 ff 83 c3 10 e2 cc 66 61 c3 e8 64 00 4d |.........fa..d.M|
00000120 75 6c 74 69 70 6c 65 20 61 63 74 69 76 65 20 70 |ultiple active p|
00000130 61 72 74 69 74 69 6f 6e 73 2e 0d 0a 00 66 8b 44 |artitions....f.D|
00000140 08 66 03 46 1c 66 89 44 08 e8 2f ff 72 13 81 3e |.f.F.f.D../.r..>|
00000150 fe 7d 55 aa 0f 85 04 ff bc fa 7b 5a 5f 07 fa ff |.}U.......{Z_...|
00000160 e4 e8 1f 00 4f 70 65 72 61 74 69 6e 67 20 73 79 |....Operating sy|
00000170 73 74 65 6d 20 6c 6f 61 64 20 65 72 72 6f 72 2e |stem load error.|
00000180 0d 0a 00 5e ac 20 c0 74 0c b4 0e 8a 3e 62 04 b3 |...^. .t....>b..|
00000190 07 cd 10 eb ef cd 18 f4 eb fd 00 00 00 00 00 00 |................|
000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fe |................|
000001c0 ff ff ee fe ff ff 01 00 00 00 27 40 06 00 00 fe |..........'@....|
000001d0 ff ff af fe ff ff 28 40 06 00 30 a1 7e 02 00 fe |......(@..0.~...|
000001e0 ff ff af fe ff ff 58 e1 88 02 08 20 ae 00 80 fe |......X.... ....|
000001f0 ff ff 83 fe ff ff 60 01 37 03 de 0e e9 02 55 aa |......`.7.....U.|
00000200

=============

[cyberdork33]

I can confirm this indirectly. I was attempting to clear the bootloader data from the MBR awhile back and this caused the flashing question mark. I had to restore my MBR backup to have it bootable again.

[pxwpxw]

More -
MBR bootable, partitions OK.
Open gparted, EFI partition, manage flags, tick boot off, decide not to, tick boot back on.
Exit without applying anything "no changes" nothing to apply.
Result -
MBR is bombed back to GPT version, no MBR boot.
====

[cyberdork33]

Progress!
https://bugs.edge.launchpad.net/mactel-support/+bug/222126