--cut here--
this is a known bug in probably libc in CentOS6 or equivalent RHEL.
Workaround is to disable recvmmsg backend on configure with configure
flag "--enable-recvmmsg=no"
$ cd knot-src
$ autoreconf -if
$ ./configure --enable-recvmmsg=no
$ make && sudo make install
For more information see:
--cut here--
I guess we should add a new section on the web with known caveats.
Ondrej
On 11. 3. 2013, at 18:15, Jan-Piet Mens <jpmens.dns(a)gmail.com> wrote:
  Hello,
 I'm pretty sure I have tomatoes (or other vegetables) on my eyes, but
 Knot won't answer UDP queries here, running on Centos 6.3 in an OpenVZ
 container. This is the minimal configuration and the results I'm seeing:
 $ knotc -V
 Knot DNS, version 1.2.0-rc3
 $ cat knot.sample.conf
 system {
  identity "knot 1.2-rc2";
  storage "/etc/knot";
 }
 interfaces {
  my-iface { address 127.0.0.1@53; }
 }
 zones {
  
example.com {
    file "example.com.zone";
  }
 }
 log {
  syslog { any info, debug, notice, warning, error; }
 }
 $ knotc -c knot.sample.conf start
 2013-03-11T18:07:44.244202+01:00 Starting server...
 2013-03-11T18:07:44.244337+01:00 Zone 'example.com.' is up-to-date.
 $ netstat -anp
 Active Internet connections (servers and established)
 Proto Recv-Q Send-Q Local Address               Foreign Address             State
PID/Program name
 tcp        0      0 127.0.0.1:53                0.0.0.0:*                   LISTEN
11408/knotd
 tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN
486/sshd
 tcp        0      0 172.16.153.104:22           172.16.153.1:64881          ESTABLISHED
554/sshd
 tcp        0      0 :::22                       :::*                        LISTEN
486/sshd
 udp        0      0 127.0.0.1:53                0.0.0.0:*
11408/knotd
 unix  2      [ ]         DGRAM                    8840414 11408/knotd
 $ dig @127.0.0.1 
example.com any
 ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6_3.6 <<>> @127.0.0.1
example.com a
 ; (1 server found)
 ;; global options: +cmd
 ;; connection timed out; no servers could be reached
 $ dig +tcp @127.0.0.1 
example.com a
 ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6_3.6 <<>> +tcp
@127.0.0.1 
example.com a
 ; (1 server found)
 ;; global options: +cmd
 ;; Got answer:
 ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20248
 ;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 ;; WARNING: recursion requested but not available
 ;; QUESTION SECTION:
 ;example.com.                  IN      A
 ;; AUTHORITY SECTION:
 
example.com.           60      IN      SOA     localhost. root.localhost. 1997022700
28800 14400 3600000 86400
 ;; Query time: 2 msec
 ;; SERVER: 127.0.0.1#53(127.0.0.1)
 ;; WHEN: Mon Mar 11 18:08:32 2013
 ;; MSG SIZE  rcvd: 79
 Mar 11 18:07:44 knot knot[11408]: Binding to interface 127.0.0.1 port 53.
 Mar 11 18:07:44 knot knot[11408]: Configured 1 interfaces and 1 zones.
 Mar 11 18:07:44 knot knot[11408]:
 Mar 11 18:07:44 knot knot[11408]: Loading 1 compiled zones...
 Mar 11 18:07:44 knot knot[11408]: Loaded zone 'example.com.' serial 1997022700
 Mar 11 18:07:44 knot knot[11408]: Loaded 1 out of 1 zones.
 Mar 11 18:07:44 knot knot[11408]: Starting server...
 Mar 11 18:07:44 knot knot[11408]: Server started as a daemon, PID = 11408
 Mar 11 18:07:44 knot knot[11408]: PID stored in /etc/knot/knot.pid
 Can you please help me open my eyes?
 Thanks,
        -JP
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