====== Logging configuration ======
<code>
logging{
  channel simple_log {
    file "/var/log/named/bind.log" versions 3 size 5m;
    severity warning;
    print-time yes;
    print-severity yes;
    print-category yes;
  };
  category default{
    simple_log;
  };
};
</code>
<code>
logging {
     category default { default_syslog; default_debug; };
     category unmatched { null; };
};
</code>

http://stackoverflow.com/questions/11153958/how-to-enable-named-bind-dns-full-logging