Re: determining root mounting point from GRUB command line prior to boot

[Nathan Stratton Treadway]

On Mon, May 27, 2019 at 22:16:29 +0000, Blue Upsilon via Help-grub wrote:
> thanks Steve;  but this does not solve my problem.
> to be more clear this is what i do when i boot:
> ======
> grub> set root=(hd0,gpt4)
> grub> linux /vmlinuz root=/dev/nvme0n1p4
> grub> initrd /initrd.img
> grub> boot
> ======
> 
> this works;
> but line #2  can be problematic in some cases.
> say i'm booting from an external disk backup.
> then in line 2,    i don't know what to set root equal to.
> if I do:     ls  /dev    then it does not show the various 
> sda1,sdb2,nvme0n1p4; etc etc.

To avoid needing to know the /dev/XXX device name ahead of time, many
linux distros now support specifying the root= parameter via a boot-time
search argument.

For example, my Ubuntu Bionic box uses
  linux   /boot/vmlinuz-4.15.0-50-generic 
root=UUID=eba1a816-77e8-11e8-898b-b8aeeddbdbb5 ro
and thus can find the desired root filesystem no matter what /dev/XXX
file it happens to get assigned on a particular startup cycle.

For manually typing in something in to a Grub prompt,
root=LABEL=.... would probably be easier to use than the UUID.

But you'll need to check the docs for your distro to see what it
supports....

                                                Nathan

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