Re: How to install grub onto an added drive?

[Chris Green]

On Mon, Nov 18, 2019 at 08:20:44PM +0100, Pascal Hambourg wrote:
> Le 17/11/2019 à 20:20, Chris Green a écrit :
> > 
> > I want to add a new SSD to my current desktop system.  This in itself
> > isn't a major problem, I've done similar things before without
> > problems (in fact I did this already with the current small and
> > relatively slow SATA SSD that has the / filesystem on it).  The issue
> > is that I suspect the motherboard won't be able to boot from the new
> > NVME/PCIe SSD so I'm aiming to have a small, bootable drive to just
> > provide the boot files and have everything except for /boot on the
> > new, fast, SSD.
> 
> If the motherboard has an M.2 slot with NVMe support, the firmware should be
> able to boot from an NMVe SSD. If it has no M.2 slot and you added the NMVe
> SSD with a PCIe adapter card, it is unlikely the firmware is able to boot
> from an NVMe SSD.
> 
You have the situation *exactly* right, I'm aiming to add an NMVe SSD
using a PCIe adapter card.


> > So, I can move all the required OS files to the new hard disk but how
> > do I get grub installed on whatever I have as a 'small' boot disk?
> 
> You must install not only GRUB but the whole /boot on the boot drive.
> 
Yes, sorry, I realise I have to put the whole of the contents of /boot
onto the 'small' boot disk.


> > Basic questions:-
> > 
> >      Presumably the disk where the /boot filesystem is has to be marked
> >      bootable using fdisk.
> 
> You cannot mark a whole drive as bootable. You can mark a primary partition
> as bootable, but this is needed only with broken firmwares which require it.
> A compliant BIOS does not require a bootable partition.
> 
Ah, OK, I hadn't realised that (that marking bootable isn't
necessary).  How does the BIOS decide what disk to boot from then,
does it search for the MBR signature?


> >      How do grub-install and grub-mkconfig relate to each other?
> 
> grub-install installs GRUB in the specified locations and grub-mkconfig
> generates a configuration script on its standard output that you can write
> to the location where GRUB expects to find it, by default
> /boot/grub/grub.cfg. update-grub must be run from the target system
> (natively or chrooted). grub-install can be run from any other system if you
> specify the --boot-directory= location.
> 
> >      Which do I run first?
> 
> It does not matter.
> 
> >  Do I need to run both?
> 
> Yes.
> 
OK, thanks, this is all really useful.


> >      What do I need to tell them (parameter-wise)?
> 
> In BIOS/legacy mode, grub-install takes at least one parameter : the device
> node you want to install GRUB on. grub-mkconfig takes no parameter.
> 
> >      Is there anything else I need to do?
> 
> Update fstab and the initramfs.
> 
OK, fstab is easy enough.  Do I just run update-initramfs for the
initramfs?

Thanks for all this, it's becoming clearer, slowly.

-- 
Chris Green