[NTLUG:Discuss] booting from different root partitions

[kbrannen@gte.net]

Jack Snodgrass wrote:
...
> My drive is set up like this
> /dev/hda1 - /boot
> /dev/hda2 - primary-root-partition
> /dev/hda3 - backup-root-partition
> 
> Now... I normally boot and have /etc/fstab and /boot/grub/grub.conf
> set up /dev/hda2 as / and set up /dev/hda3 as /other_root. 
> 
> I use rsync to backup / to /other_root. 
> 
> Say that I have grub have these options:
> 
> title Red Hat Linux (2.4.20-18.8)
>         root (hd0,0)
>         kernel /vmlinuz-2.4.20-18.8 ro root=/dev/hda2
> 
> title Red Hat Linux (2.4.20-18.8) backup
>         root (hd0,0)
>         kernel /vmlinuz-2.4.20-18.8 ro root=/dev/hda3
> 
> I can boot the "title Red Hat Linux (2.4.20-18.8)" grub label just
> file. It's when I boot the 'backup' label that things go wrong. 
> 
> When I rsync'd the / to /other_root, both of the /etc/fstab files 
> contain:
> /dev/hda2               /            ext2    defaults        1 1
> /dev/hda3               /other_root  ext2    defaults        1 2
> 
> 
> which is right for the 'non-backup' grub lable, but incorrect for 
> the backup version. The backup version should use:
> /dev/hda2               /other_root  ext2    defaults        1 2
> /dev/hda3               /            ext2    defaults        1 1
> 
> so... how can I use the 'SAME' /etc/fstab file but have 
> different 'root' partitions? 
> 
> I know that I can rsync, and then modify the /other_root/etc/fstab
> file afterwards, ... but I'd like to avoid that step if possible. 

Because /etc needs to be "stand alone", sym links are out; you must use 
physical copies.  I think about the best you can do is create your own "grub" 
command, after you "mv grub grub.orig".  Make something like this your new "grub":

#!/bin/sh
cp -p /etc/fstab /other_root/etc/fstab
/sbin/grub.orig    # or whereever grub lives, i don't use it

That way, the "normal" process takes care of the coping and you can forget 
about it.  In theory, you'd put this in both roots.

HTH,
Kevin