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Re: managing a multiboot without stomping the toes of other OSes

From: Felix Miata
Subject: Re: managing a multiboot without stomping the toes of other OSes
Date: Fri, 14 Jan 2011 07:07:17 -0500
User-agent: Mozilla/5.0 (OS/2; Warp 4.5; rv:2.0b8pre) Gecko/20101030 SeaMonkey/2.1b2pre

On 2011/01/14 16:39 (GMT+0530) Rustom Mody composed:

Installation is not the primary problem; its (semi)automatic upgrades
that mess up.

Once each OS has its own Grub installed to its very own exclusive location (/ or dedicated /boot) and GRUB_DISABLE_OS_PROBER=true is set that will no longer be a problem.

From what you are saying one problem -- auto-probing -- is solvable.
The other -- which partition is grub in -- is yet not solved (or
understood by me).

Let me try put it another way:  I want to go from one way link to two way link.
Currently sda6 boot sector points to debian. I want to have a reverse
link (probably something in /etc/default/grub or /etc/grub.d) that
tells debian that it needs to mess around only with sda6.

Once Debian's Grub has been configured exclusively on sda6, there should be no need for linking anywhere in any direction. GRUB_DISABLE_OS_PROBER=true will prevent its boot menu from being cluttered by non-Debian stanzas. To get to the Debian menu will require a kickstart from elsewhere, probably a chainloader stanza on sda3, possibly a chainloader stanza on sda5, either of which may be the answer to what you mean by "two-way/reverse link".

And if this is not doable I want help with another workaround.
Currently I maintain 3 grub.cfgs by hand (the sda5 of ubuntu the sda6
of debian and the sda3 which does chainloading).  is there some
convenient utility (other than reading octal dumps of filesystems!!)
that can tell me that this bootsector/mbr is currently setup to start
booting from this partition?

I don't think there is one that could be termed convenient if that term is taken to mean also friendly and open source. I use a cross-platform, non-free program called DFSee for partition manipulation and backup/restore that can tell me which partitions are startable, but not what will happen once startup is triggered on any particular one of them.

Grub 1 (aka Grub Legacy on Debian/*buntu) is simpler to understand, use, and manually configure, which is why I suggested you put it on sda3. From it you can easily chainload sda5 and sda6, and it won't need reconfiguring unless you add or remove partitions. Its two stanza (sda5, sda6) menu you'll have created should continue to work without need for changes at OS update time.

Installing Grub 1 to sda3 can be rather simple. How I do it:

1-boot Knoppix CD or DVD to runlevel 3 shell prompt
2-# rm /boot #Knoppix's symlink
3-# mkdir /boot
4-(mount sda3 to /boot)
5-# cd /boot
6-# ln -s . boot
7-# mkdir grub
8-cp -a the grub legacy files (stage1, stage2, *_stage1.5) from the knoppix media to /boot/grub (I start mc and look for them with its search function)
9-create or copy a file in /boot/grub
10-create a menu.lst file in /boot/grub with chainloader entries for sda5 & sda6
11-install Grub:
        # grub
        grub> root (hd0,2)
        grub> setup (hd0,2)
        grub> quit
12-install standard MBR code. I use DFSee to do this, or boot a DOS floppy and 'A> fdisk /mbr', but I'm sure there's a way to do it without DFSee while Knoppix is still booted (apparently not via fdisk, cfdisk, sfdisk or parted though). If Windows is installed to sda1 you should be able to do 'fdisk /mbr' from a command prompt window or repair boot.
13-ensure that sda3 is the only primary marked active
14-on with life

And one last (unimportant) question: how come on the grub help list I
am getting answers that dont agree with grub philosophy?? Something
strange here...

A help list is primarily populated by users for the benefit of users, more of whom have questions than answers. These people are typically familiar with real problems and workable solutions. Participation by devs is generally limited at best, and when it comes, tends to be colored theoretical more than practical, much like government policy. may be of some help in understanding concepts.
"How much better to get wisdom than gold, to choose
understanding rather than silver." Proverbs 16:16 NKJV

 Team OS/2 ** Reg. Linux User #211409

Felix Miata  ***

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