[CentOS] Re: Problem with booting/grub (?)
ssilva at sgvwater.com
Mon Sep 22 17:08:37 UTC 2008
on 9-22-2008 1:53 AM Mark Hull-Richter spake the following:
> Earlier this evening, I had the interesting experience of shutting down
> my machine (because of that lp out-of-sync problem, discussed
> elsewhere), and watching it not come back up. I admit that I changed
> out one of my DVD writers for another one, but I don't understand how
> that could have had any effect on this:
> When I restarted the machine, it came up to the point where it normally
> shows: "GRUB Loading Stage 2..."
> Except, it stopped at the "GRUB" and hung - no stage 2, no disk
> activity, nothing, just hung.
> One of the changes I made a little while ago was to modify the boot
> order of my drives. I had been booting off of the hda drive, but now
> I'm booting from the sda drive. I went through the "grub-install
> /dev/sda" back then, then fixed the grub.conf because the disk id for
> the root was wrong (it was showing hd2, but in order to boot, this had
> to be set to hd0 because grub couldn't find anything on hd2 - weird,
> 'cuz that's where the /boot and / partitions both live, but I digress).
> I thought I'd be able to recover from this by booting from hda again,
> but that didn't work. So I put in my Live CD, booted from that and
> tried to fix it via grub-install from there - no go. Grub couldn't find
> /dev/mapper/livecd-rw (which wasn't there, although /dev/mapper/live-rw
> was - is that a bug in the live cd?)
> Then I went to my installation DVD, booted up into linux rescue mode
> (which took a few tries because I forgot to boot with linux rescue
> noapic), chroot'd to the right /dev and THEN I could finally run
> grub-install, and finally, the system rebooted from /dev/sda.
> I'm wondering:
> 1) What would cause the system not to get to the "Loading stage 2" part
> but be able to load GRUB? This one is really the key - if I can
> understand this, I can prevent it from happening again.
Grub boot code is in the mbr so it loads. If it can't find the stage 2 it
usually quietly dies. I believe it has to load stage 1 to have enough code to
actually give error messages. The mbr is just too small to get all the code
into. So changing drives also changed the bios disk order on your system, and
grub got confused.
> 2) What's with the live CD not being able to run grub-install properly?
> (It also would not install using grub - I don't recall the exact error
> message, but it was something about there not being a stage 1 area on
> the drive, which makes no sense because it _does_ boot from that drive).
The live CD isn't really a proper rescue disk for grub, but it is adequate to
copy/move data off. I wish it had the rescue cd code from an install disk at
least as a boot option.
> 3) Is this the only way to recover from such an error (GRUB, no stage 2,
> not the lp error), or was there an easier way I missed?
> My configuration is:
> OS : CentOS 5.2 (2.6.18-92.1.10 Linux kernel) x86_64 with latest updates
> AMD Athlon 64 x2 4200+ (2 x 2.0GHz), ECS NFORCE4M-A
> 4GB OCZ DDR2 800MHz (PC6400)
> /dev/hda Maxtor 160MB PATA UDMA-133
> /dev/hdb Maxtor 120MB PATA UDMA-133
> /dev/sda Seagate 300GB SATA-150/300
> /dev/sdb WD 320GB SATA-150/300
> /dev/hdc Pioneer 1810 (DVR-112D) 18x DVD+/-RW/DL
> /dev/hdd Pioneer 1810 (DVR-112D) 18x DVD+/-RW/DL
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