Re: grub-uninstall

[Pascal Hambourg]

Le 08/11/2022 à 21:00, Narcis Garcia a écrit :
> El 8/11/22 a les 20:43, Pascal Hambourg ha escrit:
> > Le 08/11/2022 à 12:00, Narcis Garcia a écrit :
> > > My mistake was to do "grub-install /dev/sda" when I need to boot from 
> > > /dev/sdb
> > >
> > > Now I've done "grub-install /dev/sdb" but I don't want GRUB messages 
> > > appear on /dev/sda when BIOS boot goes there. It's confusing.
> > >
> > > I want to know how to revert actions done by grub-install on first 
> > > disk sectors, without losing partitions.
> >
> > AFAIK, grub-install does not back up copy the original contents of 
> > sectors the boot image and core image are written to. So the best you 
> > can do is overwrite GRUB's boot image in the MBR with another boot 
> > program, e.g. with install-mbr from package "mbr".
>
> I wish at least to overwrite MBR program without wiping partition table 
> AND clean (with zeroes) next sectors written by grub-install.

First save the MBR with

 dd if=/dev/sda of=sda.mbr bs=512 count=1

Then you can wipe the boot image in the first 440 bytes of the MBR and 
preserve the partition table with

 dd if=/dev/zero of=/dev/sda count=1 bs=440

IMO it is not worth wiping the core image sectors. They are useless 
without the boot image.