Re: Towards a customized Grub2

[John Little]

Richard Owlett asked for a grub2 customized to his wishes.

>How to obtain and install?

(This from memory before I got an UEFI computer.  Please, anyone,
criticize the following.)

I think you're headed for a hand-coded grub.cfg.  There's a learning
curve, but in the long run, say the life of a PC, if you're running
several installs, reinstalling occasionally, IMO it's easier that way.
  A lot of what people see as part of Grub, like the "OS prober",
"update-grub", and custom entries in /etc/grub.d belong to debian, and
grub is agnostic about them.

The main trouble with the generated grub.cfg was that it would change
unpredictably, and not work sometimes; grub 2 was arriving during
those years.  Or, I'd move a partition, add a disk, or do an install
and get the grub rescue prompt.

1) I imagine the default gap to the first partition (1 MiB less 1
sector) will be enough, as I'm not suggesting you add any modules to
what goes there.  However, in 2017, perhaps more is needed now.
/boot/grub is 8.9 MiB on my system, but if you want background images
and fonts they'll need space.  I suggest 100 MiB for /dev/sda1.

2) "will contain the default OS" implies you haven't installed it yet.
When you install it, if possible tell the installer to put grub on
/dev/sda3.  (My installer is Ubuntu's one, ubiquity, and it asked that
question.)  The grub code in the MBR and the gap will point to
/dev/sda3/boot.  When your debian updates with a new kernel, you don't
want debian updating grub on /dev/sda1. When you install other OS's,
don't let them install grub to /dev/sda.

2) Boot that OS, then (as root) mount /dev/sda1, say on /mnt/grub,
mkdir /mnt/grun/boot, then run grub-install /dev/sda
--boot-directory=/mnt/grub/boot.  The grub in the MBR and the gap will
now point to /dev/sda1/boot.  Have bootable media handy, in case
something goes wrong.

3) Edit /dev/sda1/boot/grub.cfg.  At the least change the first entry,
for your default OS, to search for the label you give it, not the
UUID, and to load /vmlinuz and /init.rd, some thing like:

search --no-floppy --label <your-label>
linux /vmlinuz
initrd /init.img

Those are symbolic links to the latest kernel and initrd; debian
updates them when getting a new kernel.  Now, no need for grub.cfg to
be updated when a new kernel arrives.

4) I used to add an "others" menu entry:

menuentry "others" {
    search --no-floppy --label --set=root <my-label>
        configfile /boot/grub/grub.cfg
}

This just gets to debian's updated grub, with all it's bells and
whistles, memdisk, older kernels, and whatever annoying change would
arrive.  I would also rip out most of the beginning of grub.cfg, and
refactor the insmod statements that appeared in every menuentry,

5) Every year or so, I'd have a look at where the debian grub.cfg had
got to, and see if I wanted the changes.

Regards, John Little