[systemd-devel] Why we need to read/save random seed?

Greg KH gregkh at linuxfoundation.org
Sun Jun 14 14:45:43 PDT 2015

On Sun, Jun 14, 2015 at 02:11:53PM -0300, Cristian Rodríguez wrote:
> On Sun, Jun 14, 2015 at 1:43 PM, Greg KH <gregkh at linuxfoundation.org> wrote:
> > On Sun, Jun 14, 2015 at 12:49:55PM -0300, Cristian Rodríguez wrote:
> >>
> >> El jun. 14, 2015 10:21, "cee1" <fykcee1 at gmail.com> escribió:
> >> >
> >> > Hi all,
> >> >
> >> > Why we need to read/save random seed? Can it be read from /dev/random each
> >> time?
> >>
> >> Because the kernel is borked and still is needs to be fed of entropy at system
> >> startup by user space. Please read the random man page.
> >>
> >> I agree we shouldn't have to do this at all..
> >
> > Really?  And how do you suggest we "fix" the kernel when the hardware
> > itself doesn't provide us with a proper random number "seed" in the
> > first place?  What do you suggest we do instead?
> Las time I checked , it required this userspace help even when the
> machine has rdrand/rdseed or when a virtual machine is fed from the
> host using the virtio-rng driver.. (may take up to 60 seconds to
> report
> random: nonblocking pool is initialized) Any other possible solution
> that I imagined involves either blocking and/or changes in the
> behaviour visible to userspace and that is probably unacceptable
> .

Really?  A lot of changes went into seeding the initial random generator
in the kernel in the past year, you might want to try it out again.

> The random-seed tool also does not increment the entropy count (It
> writes to /dev/random instead of using the ioctls) so the ultimate
> result is still a system with very little entropy to go on, only
> starting rngd or haveged *very* early in the boot sequence seem to
> help.

Then why not fix the random-seed tool to use the correct interface?


greg k-h

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