[Beowulf] /dev/random entropy on stateless/headless nodes

Stuart Barkley stuartb at 4gh.net
Fri Feb 25 15:08:09 PST 2011

We have a couple of clusters with headless, diskless and stateless
nodes using CentOS 5.  One of our users just ran onto a problem with
/dev/random blocking due to the lack of entropy.

I had the user change the program to use /dev/urandom and this has
handled the immediate problem.

/proc/sys/kernel/random/entropy_avail shows 0 across the compute
nodes even just after boot.

It appears that our Ethernet and Infiniband drivers don't add any
entropy to the random pool.

hw_random/intel-rng doesn't seem to work on our systems.

Some questions:

Do others have this problem?  What do you do?

Do you just refer users to /dev/urandom?

Do you modify network drivers to introduce entropy?

Are there other suggested methods of adding entropy to /dev/random?

Are there ways to introduce entropy from the random number generator
on some Intel systems?  Did Intel remove this from more recent chips?

How reliable is /dev/urandom without initial entropy?  We boot from
stateless disk images and don't carry any entropy over from previous
boots.  /dev/urandom appears to be different across several servers
just after boot, but I have not found any other initialization of the
entropy pool.  I haven't checked that single systems get different
results on different boots.  I'm concerned about users getting poor
random numbers from what should be good sources.

Thanks for any suggestions,
Stuart Barkley
I've never been lost; I was once bewildered for three days, but never lost!
                                        --  Daniel Boone

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