[Unbound-users] Unbound periodically stops responding

W.C.A. Wijngaards wouter at NLnetLabs.nl
Wed Apr 6 06:06:12 UTC 2011

Hash: SHA1

Hi Will,

On 04/06/2011 03:01 AM, Will Roberts wrote:
> Hi,
> I'm using unbound 1.4.6 on 40ish machines, and for the most part it
> works fantastically. On one my machines however it seems to randomly
> stop responding. I'm not convinced the fault here lies with unbound, but
> as far as I can tell it's the only thing that seems to fail (which
> triggers everything else since they can no longer resolve anything).

That sounds bad.

> When this issue happens, I can't communicate with unbound via
> unbound-control and it will never resolve anything. I can cleanly shut
> it down and start a new instance and it will behave exactly the same.
> The only solution I've found is to restart the VPS. I have another VPS
> from the same provider which is setup almost identically and it has
> never had this issue.

So, it is somehow unique to that machine.  Can you see in 'top' what
unbound is doing?  (is it using cpu, 100% in a busy loop?, it is not
responding to unbound-control, so it must be completely hosed somehow)

netstat -su may be interesting (packet counters for UDP).

Another thing you can do is use 'gcore' to make a coredump of the
'failed' unbound process.  (and then kill it and start a new unbound for
your production).  Then you can use 'gdb' and your compiled unbound
executable to read the core image and produce a stack backtrace what it
is doing.

> I've got debug logging on and the log file has dozens of requests per
> minute up until the issue occurred, then nothing until it received
> SIGTERM and shut down. The next time this happens (could be
> hours/days/weeks) is there anything else I can check that would explain
> why it does not appear to be even receiving the lookup requests?

Well it should respond to the unbound-control utility.  If it does not
this means it is somehow no longer processing the main loop, or that
network traffic does not reach it.

Best regards,
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