Re: How do I mount the USB stick containing the installer in Rescue Mode?

From	David Wright <deblis@lionunicorn.co.uk>
Newsgroups	linux.debian.user
Subject	Re: How do I mount the USB stick containing the installer in Rescue Mode?
Date	2021-07-16 06:50 +0200
Message-ID	<CBnXs-6Cc-5@gated-at.bofh.it> (permalink)
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On Thu 15 Jul 2021 at 22:15:59 (+0200), Stella Ashburne wrote:
> > Sent: Thursday, July 15, 2021 at 7:08 PM
> > From: "David Wright" <deblis@lionunicorn.co.uk>
> >
> > Best I can do. (And I see that your kernel's naming of sda/sdb
> > is more stable than on at least a couple of my machines.)
> >
> What did you mean by "more stable"?

(Greg covered this.)

> > It might be worth posting a request for the stanza I asked for,
> > but as a new topic with a specific Subject line.
> 
> What "stanza" were you referring to? Was it Reco who posted it? And you wrote that it was posted some time in June?

The /full/ stanza is next, but Grub probably makes this look more
complicated by adding more flexibility than any one user could
ever need. (It's GRand Unified …, after all.)

menuentry 'Debian GNU/Linux' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-80318fa0-5915-4cc3-bc7c-99af2cfbfda9' {
	load_video
	insmod gzio
	if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
	insmod part_gpt
	insmod ext2
	set root='hd0,gpt2'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  700b607c-ffa6-4435-a4b6-10894928c764
	else
	  search --no-floppy --fs-uuid --set=root 700b607c-ffa6-4435-a4b6-10894928c764
	fi
	echo	'Loading Linux 5.10.0-7-amd64 ...'
	linux	/vmlinuz-5.10.0-7-amd64 root=UUID=80318fa0-5915-4cc3-bc7c-99af2cfbfda9 ro  quiet
	echo	'Loading initial ramdisk ...'
	initrd	/initrd.img-5.10.0-7-amd64
}

That boots the encrypted root installation that I made the other day,
but I can boot the system manually just by typing C at the grub menu,
and then:

Grub> set root='hd0,gpt2'
Grub> linux /vmlinuz-5.10.0-7-amd64 ro quiet root=UUID=80318fa0-5915-4cc3-bc7c-99af2cfbfda9
Grub> initrd /initrd.img-5.10.0-7-amd64

or the second line can be shortened to:

Grub> linux /vmlinuz-5.10.0-7-amd64 ro quiet root=LABEL=viva05

or even:

Grub> linux /vmlinuz-5.10.0-7-amd64 ro quiet root=/dev/dm-0

because, once the disk's 5th partition has been unlocked,¹ any of
these properties describes the filesystem inside².

> > I can't see
> > why you shouldn't be able to boot your system with manual Grub
> > commands.
> 
> I thought so too. GRUB developers would and should have built a "Rescue Mode" by just entering the commands.

They have, and you're using it. No, what I meant was that you should
be able to boot it, just giving the correct raw commands. The problem
is knowing what those correct commands are.

¹ Skip this; it's just for the record. Before I made this encrypted
  installation, I posted that you might need to load Grub modules
  like crypto, cryptodisk and luks. However, I now think that these
  modules may exist for unlocking /boot (which would have to be done
  by Grub) rather than / (which can be left for initrd to do).

² root=UUID=80318fa0-5915-4cc3-bc7c-99af2cfbfda9 was copied from grub.cfg,
  root=LABEL=viva05 was a LABEL set in the screen dialogue already posted,
  root=/dev/dm-0 was the device mapper I observed when I first booted the
  system (using Grub's menu).

Cheers,
David.

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