Stephen Gran on 4 Jul 2006 12:50:57 -0000


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Re: [PLUG] wtf? system out of entropy


On Tue, Jul 04, 2006 at 07:29:35AM -0400, sean finney said:
> hey stephen,
> 
> On Tue, Jul 04, 2006 at 11:22:59AM +0100, Stephen Gran wrote:
> > find / > /dev/null 2>&1
> 
> that was like the first thing i tried :)

:)

> > etc.  Sometimes you can generate enough entropy to get back in the black
> > by really working the disks, but often not.
> 
> i've tried working some of the SATA disks like above without luck,
> but maybe there's something else i can use to generate even more
> i/o?  for example, hdparm -tT would be a good candidate, only these
> are showing up as scsi...

steve@gashuffer:~$ sudo hdparm -Tt /dev/sda

/dev/sda:
 Timing cached reads:   3296 MB in  2.00 seconds = 1648.71 MB/sec
 Timing buffered disk reads:  186 MB in  3.02 seconds =  61.65 MB/sec

<hdparm maintainer hat on>
hdparm 6.6 works just fine for SATA.  Some of the ioctls are no ops, but
it doesn't do anything harmful.

> > Is this a 2.6 Debian stable kernel?  The 2.6.8 kernel was at the moment
> 
> nope, it's a 2.4.27 kernel, homerolled using the debian config with one
> or two unrelated options changed (needed for RAID or detecting the
> controller properly, i forget off-hand)

Hrmph.  I really don't know then.  Do you have hw-random (or whatever
it's called) loaded?  Does your board support any other entropy
gatherers?

> also, i was inspired to see how the random seed is initially set, and
> tried catting some stuff onto /dev/urandom (as is done in the
> urandom.sh init script), but still no luck.

A way forward (that is not really optimal, but I have heard of people
doing it on systems where they can't get enouogh entropy) is to rm
/dev/random, and link random to urandom.  You get non-blocking IO in
exchange for only kinda pseudo random numbers.

Good luck.  I've been struggling with a couple of servers with this
problem, but fortunately for me, 2.4.27 from Debian gave me enough
entropy to get by.
-- 
 --------------------------------------------------------------------------
|  Stephen Gran                  | I will follow the good side right to    |
|  steve@lobefin.net             | the fire, but not into it if I can help |
|  http://www.lobefin.net/~steve | it.   -- Michel Eyquem de Montaigne     |
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