Update Grub after modifying fstab?

[Jose I Diaz Bardales]

On 1/30/20 3:06 AM, Volker Wysk wrote:
> Am Mittwoch, den 29.01.2020, 18:37 -0500 schrieb Jose I Diaz Bardales:
>> On 1/29/20 3:15 PM, Volker Wysk wrote:
>>> Hi
>>>
>>> The ubuntu installer sets up LVM, when choosing encryption. I want
>>> to
>>> rename the volume group. It is always set to "ubuntu-vg" by the
>>> ubuntu
>>> installer. I want to avoid volume group name clashes in the future.
>>>
>>> In the process of doing this, the /etc/fstab file needs to be
>>> changed.
>>> Amongst other things, it contains the line for the root filesystem.
>>> For
>>> instance:
>>>
>>> /dev/mapper/ubuntu--vg-root / ext4 errors=remount-ro 0 1
>>>
>>> Now "ubuntu-vg" shall be renamed to "desktop-vg":
>>>
>>> /dev/mapper/desktop--vg-root / ext4 errors=remount-ro 0 1
>>>
>>> Does this break the bootability of the system? In other words, does
>>> Grub need to be updated when changing /etc/fstab? The renaming
>>> needs to
>>> be done from a live/maintenance system, because otherwise the VG to
>>> be
>>> renamed is being in use. (really?)
>>>
>>>   From what I've learned, the following command sequence is needed
>>> to
>>> make the system bootable again, in the case of an UEFI system. The
>>> system is mounted at /mnt/root:
>>>
>>> mount <boot/-partition> /mnt/root/boot
>>> mount <boot/efi/-partition> /mnt/root/boot/efi
>>> mount --rbind /dev /mnt/root/dev
>>> mount --rbind /proc /mnt/root/proc
>>> mount --rbind /sys /mnt/root/sys
>>> chroot /mnt/root
>>> update-initramfs -u
>>> grub-install --target=x86_64-efi --efi-directory=/boot/efi --
>>> bootloader-id=Desktop
>>> update-grub
>>>
>>> So
>>> - Is this necessary?
>>> - Is the grub-install line correct?
>>>
>>>
>>> Cheers,
>>> Volker
>>
>> I am not 100 percent sure but I believe you can use the lvm utility
>> to
>> rename volume groups without the need to edit fstab.
> 
> The fstab needs to be modified, since in it occurs the volume group
> name. Maybe (I don't think so) the lvm tool does that, but then the
> system still needs to be made bootable again. I think that, otherwise,
> the initramfs still contains the old volume group name.
> 
> Volker
> 
Hello Volker,

I was curios about this and you are correct. I added 2 virtual 
hard-drives on my VM at work and created a logical volume, and I did 
have to modified the fstab file at the end.

Let me point out that I am doing all this on VM with a OS already 
install and I am not using encryption.

Hopefully someone with more experience can provide some suggestions.