Re: A Grub Boot Question about initrd
First I greatly appreciate all this information as the idea is to
fix a problem I probably created long ago though I am not sure
how but the short story is that apt-get upgrade ran update-grub
and update-initramfs late last Fall and I was able to rescue it
but it happened again at the end of April so I figured I had
better fix it correctly since I didn't know it was a ticking
bomb.
Felix Miata <mrmazda@earthlink.net> writes:
> Martin McCormick composed on 2021-06-05 12:46 (UTC-0500):
>
> > I have a plan but I need some more information. Is there any
> > personalization done by the boot setup process? Do our UUID's
> > or any other specific information pertaining to the installation
> > make it in to the initrd files?
>
> Dracut includes a root=UUID=<UUID> statement in the initrd. A root=
> statement on
> the Grub linu* line overrides it. The override can be any of the accepted
> forms,
> including root=LABEL= and root=<device name>.
Good to know.
> The translation is easy. UUIDs are assigned to devices. The device names
> are
> acceptable substitutes, just as they used to be the only option before
> libata made
> device names capable of playing musical chairs. If devices also have
> labels,
> labels can be used instead of device names.
Very much like the reasoning behind udev which is a God-send if you
have multiple sound cards as one example.
> UUIDs were designed for computer scripts, not human brains. You'll need
> to make a
> conversion, but instead of UUIDs, I highly recommend using labels when
> you know
> device names will be different on the system migrated to. UUIDs are
> appropriate
> too, just rather unwieldy unless scripted.
There's 1 UUID for the root file system in /boot/grub/grub.cfg
which is the file one must not normally edit by hand. It
reads
menuentry 'Debian GNU/Linux' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-658da8df-942e-4ad7-8c5b-695f2f2eb4ed' {
> Grub provides a shell. From the shell it's possible to boot using the
> information
> you have. Instead of trying to figure it all out in advance, drop to the
> shell and
> use the device names you know. It's really not hard if you have a copy of
> a grub
> menu from the two PCs planted in your brain or on paper. Once you've
> booted, it's
> easy to fix everything up by running grub-mkconfig, and if necessary,
> /etc/default/grub.
>
> > As an aside, one ought to be able to do something like
> > this. It makes life a lot simpler. Both systems are using the
> > same kernel and versions of the same processor the only real
> > differences are the UUID's. The grub configurations of both are
> > the same down to the serial console.
>
> Don't let the massive volume of data in grub.cfg mislead you. Its primary
> job is
> to find and load a kernel and initrd. If you know where they are and
> their names,
> none of the menu components or apparent search and identification bloat
> are
> necessary. Before Grub2 you could simply tell Grub's shell the root
> device, the
> kernel name (with associated parameters, most of which aren't actually
> necessary),
> and the initrd name, then boot. With Grub2 you may need to precede the
> root device
> name with loading a module or two or three, which you see in your copy of
> a
> grub.cfg, then proceed with the important three. I do a lot of cloning,
> so I've
> done it often.
Thanks again. I was starting to get discouraged but I
will try using actual labels since I thought you really shouldn't
do that.
Martin
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