Rename the Volume Group of an USB stick, which uses LVM

[Volker Wysk]

Hi!

I'm trying to build an encrypted rescue/maintenance system on an USB
stick. Therefore, I've installed Ubuntu 20.04 on the USB stick. I'm
using the regular Ubuntu installer to do the installation, which makes
use of LVM in case of encryption of the disk. A volume group named
"vgubuntu" is created.

Now I have to rename the volume group of the system on the USB-Stick to
avoid conflicts, especially with my laptop's main system. I've had this
problem in 2017, and Xen answered my question in 2017-12-09:

-----snip-----
BEFORE you do any cryptsetup open on the main system, run:

vgrename kubuntu-vg rescue-vg

Then you must verify that /etc/fstab in the RESCUE system contains no
references to "kubuntu-vg" and you might also have to rerun
"update-grub" if you want to keep it this way.

That is all you need to do to rename the volume group.

After that you can open the crypt and it won't conflict.
-----snip-----

I've followed these instructions now, and renamed "vgubuntu" to
wartung". But the "update-grub" step doesn't work. I get the message
(translated back from German) "Canonical path of /dev/mapper/vgubuntu-
root could not be determined".

After making a symlink from /dev/mapper/wartung-root to
/dev/mapper/vgubuntu-root, the "grub-setup" works, but booting the USB-
stick fails. I get a busybox rescue shell.

So what is missing? 

Cheers
Volker