Re: Understanding Grub2

[sashab]

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.
> 
> 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.

> 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.

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.)

Hth.
Regards,
    Alex