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

[jmh6]

Hi Pascal,

    Thanks again !!

    I downloaded the latest grub CD.

    I notice that when I partition using fdisk is usually leaves some 
blocks at the beginning. I guess this is for grub?

    In any case I 'should' be able to prepare the disk using fdisk and 
then load my /dev/sda2 image where is should be. Make the swap space and 
run grub-install.

    I now have a running disk. So I will try moving the beginning of 
partition 1 and reformating it as swap and see if grub 2.02 will just 
work.

    Does grub document how much space it needs? I guess there really ought 
to be a special grub partition.

    I made two memory stick versions. One with just /dev/sda2 and one with 
the whole hard drive image. I think I can now get the /dev/sda2 image 
running and also update grub at the same time.

    Thanks to you, I think I am beginning to understand grub.

    John


On Sat, 15 Jul 2017, Pascal Hambourg wrote:

> Le 15/07/2017 ? 12:40, address@hidden a ?crit :
> >     Did this go to the list and the right thread?? 
>
> Yes it did.
>
> > I am not really sure how to make sure that is done correctly.
>
> You just have to reply to the proper mail.
>
> >     That system uses Grub 0.97.
>
> Oh, I overlooked the fact that you were using this old deprecated 
> version of GRUB, now called "GRUB legacy". I do not remember much how it 
> works.
>
> > Swap starts at block 1 [512 byte  blocks].
>
> This is bad.
> 1) This leaves no room for stage1.5 (GRUB legacy) or embedded core image 
> (GRUB 2), making the boot process less reliable.
> 2) The swap partition is not aligned on flash write/erase blocks 
> boundaries (typically up to 1 MiB), causing write performance 
> degradation and increased wear.
>
> > So I guess that what is in the MBR must find /dev/sda2 
> > /boot/stage1?
>
> No, what is in the MBR *is* stage1. And it looks for stage2 in /boot/grub.
>
> > An older version of grub I assume.
>
> Yes.
>
> > While the MBR hex is 
> > very similar to /boot/grub/Stage1 it is not identical which I would expect.
>
> The MBR also contains the primary DOS partition table.
>
> >     Next I am planning to try your grub 2.02 method. But what about swap 
> > starting at block 1. How big a space does there need to be at the 
> > beginning of the hard drive to accomodate grub?
>
> The traditional gap was 31 KiB (62 sectors). This can be too small for 
> for GRUB 2 core image. At least 64 KiB is better.
> The modern alignment boundary is 1 MiB. This is plenty enough for GRUB.
>
> What about the root partition alignment on the USB stick ?
>
> >     So I will have Linux running with the to be activated hard drive 
> > also attached as /dev/sdb and the /dev/sda2 image on a memory stick.
> >
> >     I am assuming grub will not move disk partitions to make room for 
> > itself? So I guess I have to do that first?
>
> Indeed. Instead of shrinking and moving the swap partition, is is easier 
> to delete and recreate it with proper alignment. Then with mkswap you 
> format it and give it the same UUID as the old one (as found in /etc/fstab).
>
> >     I will mount /dev/sda2 somewhere convenient and follow what you have 
> > written below.
> >
> >     After that, grub will be upgraded to 2.02 and the disk should boot.
>
> Hmm. How do you intend to upgrade GRUB on the USB stick ?
>
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