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

[Rich Freeman <r-plug@thefreemanclan.net>]

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.

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.

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

Rich
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