How to troubleshoot a frozen boot sequence

Jerry McAllister jerrymc at
Fri Jan 22 19:26:36 UTC 2010

On Fri, Jan 22, 2010 at 11:53:31AM -0600, Billy Newsom wrote:

> I am doing a test run on a production server. It has 2 hard drives.
> ad0 (mounted on /disk250 in a single slice plus SWAP)
> twed0 (mounted on / /var /usr and a SWAP)
> The twed0 is a hardware mirror and my main drive.
> ad0 is just for backups.
> What the issue is, and you probably know where I'm heading. The boot 
> process freezes if I remove the ad0 (to test a drive failure condition)
> It freezes after saying:
> BTX boot loader.... etc.

I don't see any indication that your ad0 has any provision for
hotswap.  It isn't in any raid setup.
Try taking everything from /dev/ad0 out of /etc/fstab - including
both the big partition and the swap partition and then rebooting.


> FreeBSD/i386 bootstrap loader 1.1
> It spins for a second, then stops... unless I have ad0 in the computer.
> /boot/kernel/kernel text=0x7b03a0 data=0xcdee0 /
> And it never gets to the boot menu.
> So:
> 1. Should I put a new boot0config on the twed0 drive? If so do I boot from 
> a CD to do that?
> I need to potentially do something also to my disk labels and my fstab so 
> that I don't boot to single user mode if drive ad0 fails. I haven't done 
> this exact type of thing before, so I am looking for a little help.
> my fstab:
> /dev/ad0s1b             none            swap    sw              0       0
> /dev/twed0s1b           none            swap    sw              0       0
> /dev/twed0s1a           /               ufs     rw              1       1
> /dev/ad0s1d             /disk250                ufs     rw      2       2
> /dev/twed0s1e           /tmp            ufs     rw              2       2
> /dev/twed0s1f           /usr            ufs     rw              2       2
> /dev/twed0s1d           /var            ufs     rw              2       2
> /dev/acd0               /cdrom          cd9660  ro,noauto       0       0
> I tried to read the MBR from the twed0 drive, and the program couldn't read 
> it. The one from the ad0 drive is readable and I saved a copy of it.
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