While I am writing about curious bugs, here is another one, although technically it is not really a bug.
When setting up Icinga with mod_gearman, I wondered why service-checks where running on the assigned mod_gearman worker node, but host-checks were running on the main Icinga server and were not distributed using mod_gearman. I checked the configuration again and again, but could not find an error. Also searching the web did not bring much useful information.
The only thing that I could find were hints that do_hostchecks had to set to "yes" in /etc/mod-gearman/module.conf. But according to the mod_gearman documentation, this option was set to "yes" by default.
Well, as it turns out, the flag is set to "no" by default, at least in the version of mod_gearman that is available in the software repositories of Ubuntu 12.04 LTS (Precise Pangolin). By the way, the manual that is distributed in the source archive of mod_gearman 1.2.2 (this is the same version that comes with Ubuntu) says the same, so it is not a thing that was changed recently.
Recently I stumbled across a bug in the OpenDKIM configuration of the Zimbra Collaboration Server.
In ZCS 8.0.3 (Community Edition, but I guess the same applies to the Network Edition), the file /opt/zimbra/conf/opendkim.conf.in specifies the socket that OpenDKIM listens on in the following way:
This results in the following socket address of "inet6:8465@[::1]" in the final file (opendkim.conf). However, the Postfix configuration file /opt/zimbra/postfix/conf/master.cf.in specifies the socket as "inet:localhost:8465". This leads to Postfix trying to connect to an IPv4 socket, while OpenDKIM is listening on an IPv6 socket, so that the connection cannot be established.
The fix is quite easy: By changing "%%zimbraInetMode%%:8465@[%%zimbraLocalBindAddress%%]" to "inet:email@example.com" in opendkim.conf.in and restarting Zimbra, OpenDKIM can be made to listen on an IPv4 socket, so that Postfix can connect again.
The curious thing is, that this bug has already been reported half a year ago and has supposedly been fixed. However, it seems like this fix was only applied to the 9.0 branch of Zimbra and not to Zimbra 8.0.