Re: [PLUG] Debian LVM trouble: mounting udev on /dev failed; No such device

[Isaac Bennetch <bennetch@gmail.com>]

On 4/7/2012 1:52 PM, Rich Freeman wrote:
> On Sat, Apr 7, 2012 at 11:44 AM, Isaac Bennetch<bennetch@gmail.com>  wrote:
> > My understanding is that I do have device-mapper compiled in to my
> > custom kernel. For one thing, LVM has been working fine since I last
> > compiled it a year ago. Also in my .config:
> > CONFIG_DM_CRYPT  = m
>
> Seems like the problem is with your kernel or initramfs.  Since LVM
> isn't built into the kernel (you built it as a module), you need a
> working initramfs to build.
>
> > Booting a rescue CD prompts me as to which device I want to use as the
> > root file system, selecting my LVM group; /dev/Debian/root does give
> > me access to my file system.
>
> This confirms that nothing is too messed up - the rescue CD has its
> own working kernel and initramfs.
>
> If you build your own custom kernel, you do need to make sure your
> initramfs is updated as well.  I imagine that if debian manages your
> kernel it knows to do this on its own.  However, if you compile a new
> kernel and stick it in /boot (or whever debian keeps it), then chances
> are that the kernel modules in the debian-supplied initramfs won't
> match the new kernel and won't load.  You need to rebuild your
> initramfs using whatever tools are provided by your distro, or roll
> your own (using some general tool like dracut, or from scratch).  Most
> distros have some automated tool that grabs your custom modules from
> /lib and places them into the initramfs.

Thanks for the response and sorry for my delay. I've been testing a 
number of things before responding. What you've said sounds plausible 
(and does match what I was able to find through Google), but for one 
thing: I haven't recompiled my kernel in over a year, and this system 
reboots regularly. I think something's changed recently aside from my 
kernel (which yes, I do compile myself; I do not use the Debian provided 
package).

Still, I tried to recompile with CONFIG_BLK_DEV_DM=y instead of =m, is 
there anything else I should need? That didn't change anything. After 
compiling, I did use the update-initramfs tool to update my initramfs.

> That is just a guess - I don't run Debian so I can't say for sure what
> is triggering those particular errors.  I wouldn't be surprised that
> if you ran dmesg from the shell (in the initramfs) that it showed you
> errors about modules failing to load.

Yes, correct. In fact, I'm trying to figure out specifically why I'm 
getting the message "modprobe: module dm_mod not found in modules.dep" 
(as well as a few others, but this seems directly relevant to my current 
problem).

That makes me really confused. 1) I thought I just compiled it in 
statically and 2) I thought I just updated my initramfs so my modules 
would be found.

Also, not sure if this is as relevant as I think, but from dmesg:
device-mapper: uevent: version 1.0.3
device-mapper: ioctl: 4.18.0-ioctl (2010-06-29 initilised: 
dm-devel@redhat.com

Now I'm really confused; isn't that showing that the device-mapper did 
initialize? So why else could it fail mounting my LVM partition?


> There are a bunch of other things that could go wrong, but that would
> be my first guess.
> Rich

Thanks for your thoughts

~isaac
___________________________________________________________________________
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
General Discussion  --   http://lists.phillylinux.org/mailman/listinfo/plug