Re: Breaking out of menu on "live disk", repairing grub

[Jordan Uggla]

On Mon, Mar 25, 2013 at 1:08 AM, Simon Hobson <address@hidden> wrote:
> This is probably something really simple I've missed, but ...
>
> Sometimes I have to try and repair systems, and often it is "just" a matter 
> of booting it with another grub and then running grub-install on the system 
> so it can repair it's own grub. But, for something like a Debian Live disk, I 
> can't see how to break out of the grub menu and get to specify my own kernel 
> and initrd lines.
> The specific case is where I've copied all the files to a new machine or 
> disk, so everything is there but the bootloader. Or the bootloader is damaged 
> in some way.
>
> Also, back in Grub 1 days, I could remember how to install grub just by 
> mounting the filesystem, chrooting to it, and issuing a few grub commands. 
> I've never managed to make this work with 1.99 (as currently installed with 
> Debian). Is there a simple set of commands that will do what worked in grub 1 
> (going form memory here) :
> hd0 = /dev/sda
> root = (hd0,0)
> install (hd0)

Assuming you've already chrooted (as you stated), then it's only one
command "grub-install /dev/sda". If you haven't chrooted then it's two
commands, "mount /dev/sda1 /mnt/ && grub-install
--boot-directory=/mnt/boot/ /dev/sda".

Also note that grub legacy also had a grub-install, and that your
method from the grub shell would only have worked if a proper stage2
file already existed in /boot/grub/, which is something that
grub-install would do. With grub2, grub-install copies all modules to
/boot/grub/ and generates an appropriate core.img for your particular
configuration (including support for things like
GPT,LVM,LUKS,btrfs,zfs, etc as needed to access /boot/grub/).

-- 
Jordan Uggla (Jordan_U on irc.freenode.net)