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Re: Dedicated grub2 partition

From: Barry Jackson
Subject: Re: Dedicated grub2 partition
Date: Wed, 06 Oct 2010 11:49:00 +0100
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On 06/10/10 02:36, Goh Lip wrote:

Hi Barry, I was about to give up when I saw "fromusb" in the 'test 3'
and that 'worked somewhat' up to the point of not finding the loop. Your
fairly good pics show sda, sdb and sdc.

Your iso file is not in the usb disk, right?(you said it is in sda1
root partition). Please help me understand why the "fromusb' was added
in, and if this is from the old line to boot the extracted sqsfs file,
was this extracted to the usb as well?

No, usb is not involved at all. The reason for that "fromusb" was to fix a hang during shutdown of the live session. See :-,74370.msg615449.html#msg615449

To jump the gun if it is the usb, using (hd0,x) and /dev/sdax for
booting usb and indeed other than primary hard disk is fraught with
errors (by bios, not uefi). It is best to use
"search --xxxxxxxxxxxxxxxx" and avoid (hd0,x)
Also avoid using "=/dev/sdax and use.... oh boy, don't think we can use
label or uuid here; that's why 'findiso' replaces 'isofrom=/dev/sdax"
but the problem is sometimes 'findiso' doesn't work with some livecd's.

Let's see...we can, at grub prompt, do a
<check which is the usb entry>
say, if it is really (hd0,1), then
ls (hd0,1)
<and check if it is sda1 or sdb1 or sdc1,
then modify the 'isofrom=/dev/sdyx/ ...." to the correct y and x>

Barry, note that this might change with next boot up.
ie., usb disk may become (hd2,1) instead or /dev/sdb1

Oh, if it is not on the usb, and the usb and external drives are not
required, lets, pull out all these disks so that it doesn't mess up the

No that's not the problem - I am always very careful to make sure that sda1 is actually on the first controller so that grub is not confused. hd0 is always sda here! I do not use boot USB sticks for recovery systems for that reason, as they always screw up the drive assignments - there is no point messing with grub if the drive assignments are all screwed by a USB boot!

Seriously, Barry, I was about to give up. Have been raking my brains
out. Nowadays, I only boot up iso (casper) for those 'pre-release' OS to
test out and had been installing even those "alpha 3's" (by then, fairly
okay) to disk. - reason being kernel changes cannot be made persistent-
(there are ways, but too complicated to bother with). And grml,
rescuecd, gparted, grubcd is made obsolete by my "lubuntu-on-the-stick".

Hmm.. see my point earlier about rescue systems on sticks - I avoid them.
If I boot from a CD then hd0 is sda1. If I boot from a stick, then the stick is sda1 and hd0 can be sdc - it's chaos. If I boot to my livecd in maingrub (sda1) everythig is just fine - all drive assignments are correct.

Just on that point, can grub2 use labels instead of :-
set root=(hdx,y)/...
like :-
set root=myrootlabel...
or :-
set root=LABEL=myrootlabel

That would really be nice!

Regards - Goh Lip

ps; like your tenacity :)

Well I think this may be a no-go. I just read the log-on header to the #grub IRC channel - to quote :- "It is impossible to "boot" an ISO from disk unless that image specifically supports that" which probably indicates that they are fed up with people asking the question! So maybe the ones that do work have been built with this in mind. I will do some more reading.

I only was testing it because of your suggestion. The other method of extracting isolinux and livecd.sqfs works fine.

Out of interest :-
I have also re-mastered a live cd from a working PCLOS installation (using mylivecd) after adding some extra tools, my user, and some custom configuration, and that one boots fine the same way. I had to increase the size of sda1 though for that to work as it was just too big for my 1GB partition.

Thanks for all your help, but I think we failed :-(

Cheers, Barry

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