[libvirt] "file '/dev/urandom' is not a supported random source"

Richard W.M. Jones rjones at redhat.com
Tue Apr 5 14:09:06 UTC 2016

On Tue, Mar 22, 2016 at 02:49:42PM +0000, Richard W.M. Jones wrote:
> I got this error when trying to use /dev/urandom as a backend for
> virtio-rng.  Is there a reason for that?  Plain qemu allows you to
> specify /dev/urandom and seems to work OK.
> There's a tetchy bugzilla on this subject:
> https://bugzilla.redhat.com/show_bug.cgi?id=1074464
> but I think for cases where people don't care / throwaway appliances,
> we should allow /dev/urandom.  The main reason is that it doesn't
> block.

Can we look at this again.  I'm pretty convinced after reading that
bugzilla that libvirt is plain wrong about this, even for important
appliances.  As long as the *host* has seeded the PRNG with real
entropy, seeding guests from /dev/urandom is fine.

Anyway for now I've had to disable virtio-rng in the libguestfs
libvirt backend (it's used by the direct backend, using /dev/urandom).


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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