F17 boot with lvm does not create all the device nodes

[Deron Meranda]

Continuing the exploration of my problem...

Quick problem summary:  I could not boot past emergency mode because it
could not mount /var; which is a separate filesystem than /.  My /var
filesystem is a LUKS-encrypted logical volume, which happens to be on
/dev/dm-11.  Although the logical volume itself was present and active
(shows up in lvdisplay); the lvm device file was never getting created for
it.


It is the 'udev' subsystem that is responsible for creating the device
symlinks for all the logical volumes.  I suspect that my missing device
nodes were being excluded by the "/lib/udev/rules.d/10-dm.rules" file
because the "dmsetup info" command inside it was failing.  This then caused
the "11-dm-lvm.rules" file, which normally makes the decision about
creating the symlink, to skip that device.

When I ran "dmsetup info /dev/dm-11" it failed, saying the device didn't
exist!  Yet the device file "/dev/dm-11" was present, and clearly was
usable as I could manually access the data on it, by a process such as:

  ln -s /dev/vg_xyz/lv_var  /dev/dm-11
  cryptsetup luksOpen /dev/vg_xyz/lv_var /dev/mapper/luks-xyz
  mount /dev/mapper/luks-xyz /var

So /dev/dm-11 clearly works, yet "dmsetup info" was failing for it!


Since I could manually get /var mounted, and I fortunately had enough free
space, I went ahead copied the entire filesystem into /.  [Copying details
-- I first excluded any security-sensitive files as I was going transfering
to a non-encrypted filesystem, and copied the rest of the files while
preserving SELinux contexts, and also renaming mountpoints as appropriate
so that I ended up with /var on root being an identical copy of what used
to be in the separate /var filesystem.]

After removing /var from my fstab, a reboot worked completely.
 Furthermore, when I look into the /dev/mapper directory or the device
directory for the volume group I see ALL the expected device symlinks exist
- including my old /var as well as the other missing logical volumes.  Also
"dmsetup info" now works on all of them.


I am still quite curious as to what was going on, and am wondering if I can
go back to using a separate /var logical volume.

Deron



On Mon, Nov 18, 2013 at 2:50 AM, Deron Meranda <deron.meranda at gmail.com>wrote:

> Here's some more information.  It looks like all the LVM device files that
> correspond to a device mapper minor number of 10 or greater are missing.  I
> have four such devices (logical volumes).
>
> After boot the lvm devices look like,
>
> lvhome -> ../dm-9
> lvroot -> ../dm-1
> ...
> and so on.
>
> All the devices with minor numbers < 10 appear as I expect.  However all
> the those with minor number >= 10 are missing.
>
> If I query dm directly (dmsetup ls), or just look for all dm devices (ls
> /dev/dm-*) then all of the devices show up.  It is only the symbolic links
> for the volume group that are missing.
>
> Is there a particular dm bug, or is this just a coincidence?   How can I
> get the system to boot?
>
> Thanks
> --
> Deron Meranda
> http://deron.meranda.us/
>



-- 
Deron Meranda
http://deron.meranda.us/
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