1

When Debian updated to GRUB 2 (package grub-pc), it didn't automatically upgrade the MBR. Instead it configured the old GRUB 1 installation so that it will chainload GRUB 2; that way administrators can test the new GRUB 2 configuration. If GRUB 2 failed for some reason, you still were able to boot the system with one of the old GRUB 1 entries. After testing GRUB 2 you were supposed to run upgrade-from-grub-legacy to replace the MBR, and then manually delete /boot/grub/menu.lst*.

Unfortunately, we didn't really do that on a lot of our servers, so now we have a mix of GRUB 1 and GRUB 2 MBRs, and we don't know which server is using which version. Is there any way to detect the GRUB MBR version?

1

The German Ubuntu wiki (don't worry, the information should be understandable even for people who don't speak German) seems to show an even better way:

http://wiki.ubuntuusers.de/GRUB-Umgebung_analysieren?redirect=no#GRUB-Version-in-MBR-oder-Partitions-Bootsektor-ermitteln

sudo hexdump -v -s 0x80 -n  2 -e '2/1 "%x" "\n"'  /dev/sdXY

The result can be translated with the following table:

5272    GRUB (Legacy)
aa75    GRUB (Legacy)
48b4    GRUB 2 (version 1.96)
7c3c    GRUB 2 (version 1.97 or 1.98)
020     GRUB 2 (version 1.99)
488     Grub 2 core.img
31d2    Grub 2 core.img
8053    LILO

The original wiki article contains even more IDs that can be used to identify a lot of other MBRs from other operating systems.

3
0

I have found that the third 512 byte block of a device contains the following strings when the server is still using a GRUB 1 MBR:

some-server ~ # dd if=/dev/sda bs=512 count=1 skip=2 2>/dev/null | strings
0.97
/boot/grub/stage2 /boot/grub/menu.lst

If the server is using a GRUB 2 MBR, the block won't contain any readable strings:

some-other-server ~ % dd if=/dev/sda bs=512 count=1 skip=2 2>/dev/null | strings
WVSS
Z[^_]
1
  • This method can check if GRUB-legacy is installed, but a wiped MBR will give the same result as GRUB2. – Skippy le Grand Gourou Nov 9 '18 at 22:57

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