Re: GRUB -- Debian overrides? Or maybe I just don't understand it well...
On Mon, 18 Dec 2023 at 22:15, Felix Miata <mrmazda@earthlink.net> wrote:
>
> I can't answer why Grub scripts to what the do, because I don't really use them,
> and don't need to understand much about them. Grub config files in /boot/grub/ are
> akin to scripts, but they are really simple, mainly just command scripts. The
> usual one is grub.cfg, the one os-prober feeds from other Linux installations. A
> less common one is custom.cfg. To use it requires the admin build it. When it
> exists, grub-mkconfig incorporates its use by/in grub.cfg. It actually gets called
> by default from /etc/grub.d/41_custom, which adds the stanzas from it to the Grub
> boot menu - after those that it has generated itself. I copy it to
> /etc/grub.d/07_custom, and empty 41_custom. That causes my custom stanzas to
> appear first in Grub's boot menu. /etc/grub.d/40_custom acts, and a copy of it as
> 06_custom would act, in similar fashion, except that the admin's custom stanzas
> are put into it by the admin instead of into a custom.cfg file.
>
> Thus, you, as admin, construct working stanzas however you like, with or without
> UUIDS, with or without device names, with or without volume LABELS, however you
> like boot to go, and they don't get changed, except by the admin - you. This is
> easy, because you as admin can use the kernel (and initrd) symlinks Debian puts in
> /, or anywhere you'd like symlinks to them to go, for distros that don't
> automatically create them for you. There's no need for maintenance when new
> kernels are installed in the case of Debian and other distros that automatically
> generate new symlinks. For those that don't, creating them is trivial.
>
I have just tried this, I see 41_custom in /etc/grub.d and I see that
the text from that file ends up in my grub.cfg when I run update-grub.
So I have disabled os-prober, since I won't need it if I can get this
working, and created a cusom.cfg file with approximately what
os-prober generated as manuentry stanza lines for my LFS instance
(with references to os-prober removed and the root=/dev/sdc2 changed
to root=PARTUUID=<part UUID>)
And... on reboot, the menu entry for LFS is not included.
Now looking closer at 41_custom, it says this:
#!/bin/sh
cat <<EOF
if [ -f \${config_directory}/custom.cfg ]; then
source \${config_directory}/custom.cfg
elif [ -z "\${config_directory}" -a -f \$prefix/custom.cfg ]; then
source \$prefix/custom.cfg
fi
EOF
I read that as saying if custom.cfg exists *in whatever directory is
pointed at by the variable config_directory*, then read that file. If
the directory pointed at by config_directory doesn't exist and there
is a custom.cfg in whatever directory is pointed at by the variable
prefix, use that.
The question is, what values are config_directory and prefix set to?
"prefix" is referenced in other scripts in /etc/grub.d and set to /usr
-- which is no use here as /usr is on the partition we are trying to
find so grub won't be able to see that at boot time. The only script
in that directory that references config_directory is 41_custom and it
doesn't set it. Looking at my /boot/grub/grub.cfg it doesn't contain
any references to config_directory except those that were copied from
41_custom. Am I supposed to change 41_custom or something? And if I
am, I guess I would want it to say /grub/custom.cfg since this path is
presumably relative to the root of the /boot partition, that at the
time this is being consulted that is the only partition mounted?
I feel like I am getting close but am not quite there.
Mark
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