Recommended number of threads

Alan DeKok aland at
Tue Feb 11 23:06:39 CET 2014

McNutt, Justin M. wrote:
> I've been seeing some unexplained failures to authenticate 802.1X
> clients when my system is under heavier load, and I suspect that I don't
> have enough threads running.  For reference, I currently have four
> servers in a load balanced group with identical configs.

  I hope you're doing load-balancing that is aware of EAP.

>  Thread settings are these:
>         max_servers = 32
>         min_spare_servers = 3
>         max_spare_servers = 10
>         max_requests_per_server = 0

  That should usually be OK.

> We have about 14,500 wireless clients at peak times, though that number
> will climb, I'm sure.

  i.e. about 3.5K per RADIUS server.  Unless the session timeouts are 2
minutes, that should be fine.

> Is there a rule of thumb that will tell me how many threads I should
> have (max_servers)?

  Not really.  As an FYI, I know of a large accounting system which was
running 400 threads 12 years ago. :)  *That* is a busy system.

>  Also, I suspect that there have been authentication
> failures due to all threads on a server being busy.  Is there a good way
> to confirm that?

  The server won't log a message, unfortunately.

>  I've poked around in the radiusd logs a bit, but
> haven't found much, other than the odd "Login failed" with no reason
> given.  (For "normal" failures, there are two messages, one of which has
> a cause like "bad password" or "account locked out" or some such thing.)

  Increasing the number of threads might help.  It won't hurt.

  Alan DeKok.

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