Isaac Bennetch on 12 Apr 2012 07:55:54 -0700

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

On 4/7/2012 1:52 PM, Rich Freeman wrote:
On Sat, Apr 7, 2012 at 11:44 AM, Isaac Bennetch<>  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:

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:

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.


Thanks for your thoughts

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