Xen users - Dec 2005 - Low /proc/sys/kernel/random/entropy_avail on domU

This problem came about when I noticed exim, on a domU, holding mail in 
its queue for days before delivering.

After a bit of debugging then I found gnutls was taking ages to 
calculate its keys.

So disabled TLS in exim and works fine.

Then I had another xen domU doing exactly the same thing so I did some 
more digging and came up with this post:

http://groups.yahoo.com/group/exim-users/message/85430

sure enough
/proc/sys/kernel/random/entropy_avail = 0
when mail is stuck in the queue.

Now I''ve stopped exim from using TLS again, and I don''t think
there is
much else running that could be using up the entropy, but the entropy is 
still low, max I''ve seen it is ~300. (Compaired to 3000+ on other 
non-xen boxes).

Both these servers are similar set up (although I didn''t setup the 2nd
one):

Debian - Sarge as dom0 and domU.
kernel 2.6.11.12-xen0/U
Xen 2.0 compiled from source.

So why do these boxes have low entropy, I''ve never seen this on
non-xen,
hence posting here.

Ideas welcome.

Cheers
Nathan

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Hi!

Please excuse me, but did you solve the problem with the low entropy in
the DomUs? I run in exactly the same problem, I want to apply some
cryptographic services on each DomU but

cat /proc/sys/kernel/random/entropy_avail


gives me around 250 on the DomUs but 3500 on Dom0. And I have no
cryptographic service running yet. So I bet I run low on random numbers
when I need them.

I thought of buying an USB random number generator and mount that on one
DomU but I don''t know how to feed the other domains. Maybe mounting
dev/random over nfs would work, at least locally on one machine? Or do
we have some sort of random number dispatcher in Dom0, so that having
lots of entropy there would increase the entropy on the DomUs?

Greetings,
Robert


cornet@sheepy.org schrieb:
> This problem came about when I noticed exim, on a domU, holding mail
> in its queue for days before delivering.
>
> After a bit of debugging then I found gnutls was taking ages to
> calculate its keys.
>
> So disabled TLS in exim and works fine.
>
> Then I had another xen domU doing exactly the same thing so I did some
> more digging and came up with this post:
>
> http://groups.yahoo.com/group/exim-users/message/85430
>
> sure enough
> /proc/sys/kernel/random/entropy_avail = 0
> when mail is stuck in the queue.
>
> Now I''ve stopped exim from using TLS again, and I don''t
think there is
> much else running that could be using up the entropy, but the entropy
> is still low, max I''ve seen it is ~300. (Compaired to 3000+ on
other
> non-xen boxes).
>
> Both these servers are similar set up (although I didn''t setup the
2nd
> one):
>
> Debian - Sarge as dom0 and domU.
> kernel 2.6.11.12-xen0/U
> Xen 2.0 compiled from source.
>
> So why do these boxes have low entropy, I''ve never seen this on
> non-xen, hence posting here.
>
> Ideas welcome.
>
> Cheers
> Nathan
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>

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