Re: is booting an OS without power cycling a host possible?

[Goh Lip]

On 03/18/2012 05:24 AM, Peter Van Wieren wrote:
> The running system indeed could change grub.cfg to default to
> distribution "B", and I could reboot.  "B" should start OK.
>
> My concern is that if "B" fails to boot, for whatever reason, or upon
> booting "B" I find that it lacks the tools to modify the MBR / grub.cfg
> then I will never ever be to revert the change to return the default
> distribution be "A", instead of "B".
>
> In order to avoid risking this worst-case scenario, I was hoping to find
> some alternative.
>
> Pete

[1]
You could 'set' distro B to 'mbr'
$ sudo grub-install /dev/sda

*and*
set distro A to its own partition
$ sudo grub-install --force /dev/sdaX
or
$ sudo dpkg-reconfigure grub-pc (preferably and if it applies)

both instances at their own terminals, in that order.

[2]
You could create a separate partition (less than 100MB), use that as 
/boot/grub and set that to 'mbr' and put in your custom grub.cfg there.

Goh Lip