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Re: How do I get back the GRUB menu with the blue background?

On Sun 11 Jul 2021 at 11:31:09 (-0500), David Wright wrote:
> On Sat 10 Jul 2021 at 11:13:31 (+0200), Stella Ashburne wrote:

> > My LUKS-encrypted partition consists of / and swap area. I assume the / contains /home, /var, /usr, etc...
> It would be nice to give you a set of Grub commands to manually
> boot your system with, so that you could fix up the Grub
> configuration.
> However, two things put that beyond my capabilities: encrypted
> root, and "logical volumes".
> [ … ]

Just for the record, I installed bullseye rc2 with encrypted root
on a couple of spare partitions (/boot on a borrowed ESP, and
root over an unencrypted bullseye rc1).

> Grub needs to find the kernel and initrd, and this should work
> as they're on a simple unencypted partition:
> grub> set root=(hd0,gpt2)

If this doesn't work, use single quotes.

> Now /I/ would be able to type:
> grub> linux  /vmlinuz-4.19.0-17-amd64 root=LABEL=toto04 ro systemd.show_status=true quiet
> grub> initrd /initrd.img-4.19.0-17-amd64
> but 'root=LABEL=toto04' wouldn't work for you,

Actually, this does work, as Grub doesn't have to actually find
the root filesystem: the initrd contains its partition UUID in
cryptroot/crypttab, and when that partition is unlocked, the
LABEL becomes visible. So, assuming you know the LABEL you gave
it at this stage in the installation:

  ┌────────────────────────┤ [!!] Partition disks ├─────────────────────────┐   
  │                                                                         │   
  │ You are editing partition #1 of Encrypted volume (sda5_crypt). No       │   
  │ existing file system was detected in this partition.                    │   
  │                                                                         │   
  │ Partition settings:                                                     │   
  │                                                                         │   
  │            Use as:           Ext4 journaling file system                │   
  │                                                                         │   
  │            Mount point:      /                                          │   
  │            Mount options:    defaults                                   │   
  │            Label:            viva05                                     │   
  │            Reserved blocks:  5%                                         │   
  │            Typical usage:    standard                                   │   
  │                                                                         │   
  │            Erase data on this partition                                 │   
  │            Done setting up the partition                                │   
  │                                                                         │   
  │     <Go Back>                                                           │   
  │                                                                         │   

(viva05 in this instance), you can just plug that in.

You can even give the device mapper's name for the unlocked partition:

> grub> linux /vmlinuz-4.19.0-17-amd64 root=/dev/dm-N ro systemd.show_status=true quiet

This works if you can deduce the value of N; that's simple for me
as there's only one partition involved (I didn't configure swap),
so it's simply dm-0.

You could use trial and error to work out the value, too.
It only takes a couple of minutes to type in the Grub commands
using dm-0, dm-1 etc each time, and seeing whether the kernel
finds the root filesystem. If not, reboot.

However, I don't intend getting into LVMs any time soon as I'll be
overwriting the partition above with unencrypted 11.0 whenever it's
released. So I'm no help there.


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