Re: Understanding Grub2

[Richard Owlett]

On 04/15/2018 10:58 PM, sashab wrote:
> Hi Richard,
>
> On 15/04/18 23:34, Richard Owlett wrote:
> > On 04/15/2018 09:16 AM, Goh Lip wrote:
> > > On 15/04/18 20:58, Richard Owlett wrote:
> > > > a MBR BIOS is used.
> > > > I wish to dedicate the first partition to Grub
> > >
> > >
> > >
> > > Assuming partition is sda1, from any working grub 2 bios-legacy OS in
> > > your computer.
> > > sudo mount /dev/sda1 /mnt
> > > sudo grub-install --boot-directory=/mnt/boot /dev/sda
> > >
> > > Then put in your grub.cfg in sda1/boot/grub/grub.cfg (or
> > > /boot/grub2/grub.cfg if applicable)
> >
> > I did that.
> > When booting that device, I got the expected grub command line.
> > I am now investigating what my grub.cfg should look like.
> >
> > I am reading several references listed at
> > https://www.gnu.org/software/grub/grub-documentation.html
> > especially
> > https://www.gnu.org/software/grub/manual/grub/grub.html#Invoking-grub_002dmkconfig
> >
> >
> > I suspect that
> >    grub-mkconfig -o /boot/grub/grub.cfg
> > will do what I need.

CLARIFICATION:
In my original post I had said:
> As there may or may not be a complete OS elsewhere on my device, it implies
> the functional equivalent of "update-grub" being on same partition to which
> the minimalist Grub has been installed.
It's my understanding is that "update-grub" is Debian specific.
My reading of the Gnu documentation suggested that
   grub-mkconfig -o /boot/grub/grub.cfg
would *similar* functionality.
I prefer a pure Gnu approach for "reproducibility"{best word?} reasons.
I have minor quibbles the results of Debian's approach. I wish to 
experimentally determine whether my quibbles are with Gnu or Debian.

> > There is a reference to
> >
> > https://www.gnu.org/software/grub/manual/grub/grub.html#Simple-configuration
> >
> > which has references to /etc/grub.d  and  /etc/default/grub .
> >
> > These were not created by grub-install.
> > Is there a default set somewhere?
> > Would it be safe to copy them from my current install?
>
> Those files are maintained and delivered by your distro; And used by
> grub-mkconfig.
> AFAIK those could be copied from an another install.

That addresses the "safety" issue.
Is there a Gnu prototype somewhere?


> > Are there other directories and files I'll need?
> >
> > Thank you very much.
> > I suspect you have rattled my thought patterns enough to resolve some
> > apparently unrelated conundrums ;}
>
> If i get it right, you would like to keep your boot partition portable.
> In that case you may wish to create a simple separate conf for your
> "full" install by hand like Goh already wrote.

I prefer to avoid custom manual configuration.

> However, for automating things it could work if you have os-prober set
> up on your first partition.
>
> An another option would be to make use of sh-like syntax of grub conf.
> In that case you should take a look at how GRML does it.
> (There is a conf on their iso which can be loaded by your locally
> installed grub. If you prepare such a conf for your local install, your
> could look up all partitions for such a conf and present menu entries on
> boot.)

I'll investigate.

> Hth.
> Regards,
>      Alex
Thank you.