HOW TO: Backup and clear MBR (uninstall GRUB)

[pxwpxw]

Ok, please review:
http://ubuntuforums.org/showpost.php...36&postcount=1

I think do it just using Macosx terminal, that way its easier to make and retrieve a usb MBR, you could say don't do it unless you have macosx, and emphasize that it needs refit to regen the MBR after the fakembr. Live CD would need more explaining about mounting usb or the hd root system, seems to be getting too hard.

I can pm you with an outline if you like, or put it here (tomorrow).

[cyberdork33]

I think do it just using Macosx terminal, that way its easier to make and retrieve a usb MBR, you could say don't do it unless you have macosx, and emphasize that it needs refit to regen the MBR after the fakembr. Live CD would need more explaining about mounting usb or the hd root system, seems to be getting too hard.

I can pm you with an outline if you like, or put it here (tomorrow).

I choose to do it from the Linux commandline for two major reasons:
1. This is a Linux forum, and I like to emphasize using Linux to accomplish the task. (and yes I know that dd is a UNIX tool).
2. As far as I can tell, Linux happily writes over the MBR with dd even with mounted partitions on the disk unlike OSX sometimes.


I think I will just show how to install refit in Ubuntu and sync immediately instead of relying n the reboot too.

[pxwpxw]

I choose to do it from the Linux commandline for two major reasons:
1. This is a Linux forum, and I like to emphasize using Linux to accomplish the task. (and yes I know that dd is a UNIX tool).

Yes, agreed

2. As far as I can tell, Linux happily writes over the MBR with dd even with mounted partitions on the disk unlike OSX sometimes.

Yes, I forgot macosx has problems that way.

I think I will just show how to install refit in Ubuntu and sync immediately instead of relying n the reboot too.

I think yes, fairly safe to assume the fakembr will work.

[cyberdork33]

I think yes, fairly safe to assume the fakembr will work.

Ok, I mention both as a way to sync partitions now.

[pxwpxw]

I just looked at the #1 post again.

It seems to have drifted away from the main stated purpose - to remove the duplicate tux by deleting the grub bootcode in the first 446 bytes of the MBR.
I think this probably is why most people use it.

As in the previous version, this only requires -

from Ubuntu live cd

$ sudo dd if=/dev/zero of=/dev/sda bs=446 count=1
$ sudo apt-get install refit
$ sudo gptsync /dev/sda

gptsync will report 'no need to sync' if all was well before the operation, because the partition table is untouched.

The backup mbr is always desirable.

The fake mbr was for a a separate issue of accidental damage to mbr, entirely unnecssary for removing tux which is the topic of the thread, unless something goes wrong.

[cyberdork33]

I just looked at the #1 post again.

It seems to have drifted away from the main stated purpose - to remove the duplicate tux by deleting the grub bootcode in the first 446 bytes of the MBR.
I think this probably is why most people use it.

Well, I did make it more generic than that on purpose (see the thread title).

As in the previous version, this only requires -

from Ubuntu live cd

$ sudo dd if=/dev/zero of=/dev/sda bs=446 count=1
$ sudo apt-get install refit
$ sudo gptsync /dev/sda

gptsync will report 'no need to sync' if all was well before the operation, because the partition table is untouched.

Understood, but I think that one had the same problem as doing the whole MBR (it removed that MBR header or whatever it is that allows the disk to be bootable... Maybe a dummy mbr that is only 446 bytes long?

The fake mbr was for a a separate issue of accidental damage to mbr, entirely unnecssary for removing tux which is the topic of the thread, unless something goes wrong.

Yes, I think the issue was that people following this (as well as the grub install issue that seems to cause it sometimes) were the ones with the damaged MBR.

Maybe another thread is in order.

[stillingen]

You'll still have to sync the partition tables with rEFIt and possibly reinstall grub.

Probably reinstall. I updated MBR, no go. I´ll probably drop Ubuntu, got quite friendly with OSX..

[JollyRogers]

Cyberdork, Want to personally thank you on this one. You are DA' MAN!!! I have your home page book marked btw.

I dorked my primary disk MBR up and ended up with a phantom Windows boot option... took me a while to realise that GPT/MBR kind of live together on an intel mac... I used dd and it cleaned the MBR. THANK YOU!

[flusi100]

downright silly...

could someone please post the original MBR-content of an MacBookAir 3,2?

thanks

[Dark_Ronius]

This absolutely worked for me, better than any instructions to try and fix my gpt/mbr when I solely had Mac OS on here, so thanks!

The only thing I found was that, instead of

sudo gptsync

I actually needed to type

sudo gptsync /dev/sda

However this was using the Oneiric Beta so maybe there's been some changes with the program or something.

Many thanks!