Re: How to determine which device crashes udev in boot?

On Mon, Mar 14, 2016 at 01:48:39PM +0900, iwillallways forget1 wrote:
> I'm trying to narrow which device in an NEC VF-6 causes Linux boots to
> hang, permanently, in udevadm trigger and udevadm settle.  Many Google
> searches found many pages but no tutorials on how to debug udev this
> way.
> 
>  I downloaded fresh copies of Porteus 3.1 32-bit and 64-bit.

What kernel versions are these?

>  Porteus 3.1 64-bit boots fine, udev finds everything, x Windows works
> (I told you Windows rulez), etc.  Even on this NEC VF-6.
> 
>  Porteus 3.1 32-bit boots fine on everything except this NEC VF-6, x
> Windows works, etc.
> 
>  Porteus 3.1 32-bit hangs when starting udev on this NEC VF-6.  It's
> not a 120-second timeout in udevadm settle.  It never wakes up.  The
> Caps Lock key stops toggling the Caps Lock light.  The Num Lock key
> stops toggling the Num Lock light.  Ctrl+Alt+Delete is ignored.  It
> does not appear to be a kernel panic because two of the keyboard
> lights don't flash.  It is hanged, frozen, dead.
> 
>  Booting with "3 nohotplug" works (3 tells Porteus what run level to
> use, and nohotplug is observed by both the kernel and Porteus).  In
> text mode I can do some amount of experiments.  I don't know how to do
> meaningful experiments, to try to track down which device causes the
> hang.

Try looking at the documentation of udevadm, you can manually enable the
'coldplug' options there to narrow down what hardware is causing the
problem.  Odds are, you have a kernel driver that doesn't like the
hardware and it is getting loaded automatically by udev.

good luck!

greg k-h