Re: How to boot a memory stick image of a hard drive?

[jmh6]

Hi Pascal,

   Thank you very much for your incisive answer.

   I miss the simplicity of the LILO loader or at least so it seemed at 
the time!

   I am using a Debian distro - Knoppix 6.4.3 - pretty old but known to be 
reliable.

   It sounds like I need to teach that kernel how to find and mount its 
root filesystem. Previously I would fiddle the MBR with fdisk and 
eventually get things to run.

   With the USB now in the picture, I am not sure that can be done with 
that kernel?

   At least I now have a mountable image of what could be copied onto 
another pata hard drive and probably made to run.

   Thanks again for you VERY helpful answer.

   warm regards,
   John


On Sat, 8 Jul 2017, Pascal Hambourg wrote:

> Le 07/07/2017 ? 21:51, address@hidden a ?crit :
> >    I am using latest GRUB2. I have made an image copy of a Linux system 
> > running on a hard drive with a reiser filesystem. [ dd if=/dev/sda 
> > of=/dev/sdc ] sda is a PATA hard drive and sdc is a memory stick.
> >
> >    I can mount the memory stick on a linux box and all seems OK.
> >
> >    I try to start that image with grub.
> >
> >    grub> linux (hd2,msdos2)/boot/vmlinuz
> >
> >    All seems OK. I can see on the memory stick that Grub reads vmlinuz 
> > as expected.
> >
> >    grub> boot starts the image. But the image complains that it cannot 
> > find its root filesystem.
> >
> >    I have tried many variations on the root=line to no avail.
> >
> >    grub> linux (hd2,msdos2)/boot/vmlinuz root=/dev/sda2
> >
> >    I was expecting grub to do whatever magic was needed to make the usb 
> > stick available to the kernel as /dev/sda2.
>
> GRUB does not do anything beyond loading the kernel and initramfs and 
> passing command-line parameters to the kernel. It is up to the kernel to 
> find the root filesystem.
>
> Note that :
> - The kernel provided by most common distributions cannot mount the root 
> filesystem by itself and requires an initramfs (formerly initrd) to do 
> the job.
>
> - /dev/sd* device names are nowadays considered not persistent when 
> there are more than one device, so using UUID or LABEL instead is 
> preferred. But this requires an initramfs, because the kernel cannot 
> find a filesystem UUID or LABEL. It can only find a GPT partition UUID, 
> but you use a DOS/MBR partition scheme.
>
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