[systemd-devel] simultaneous udp listeners for ipv4+6 caused systemd to go into a loop

[Thomas H.P. Andersen]

I was looking into why the unit files for talkd/ntalkd were not
working [1]. For some reason specifying these two lines in the same
socket file triggers an unfortunate behavior in systemd:
ListenDatagram=[::]:517
ListenDatagram=0.0.0.0:517

Systemd first of all fails to start the service. It then tries
starting it again and again repeatedly. This quickly reaches the limit
for failing to start a service too often. It still just continues and
it spams the journal about having hit this limit. It caused a
noticeable slow down of the computer and my log file began rotating.

I have not looked into what is going on in systemd, or whether this is
a bug or not. However it is case where I think that it could be nice
to provide a clear error message.

Maybe someone can spread some light about what is going on here? A
socket file with just one of the two ListenDatagram-lines works just
fine.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=737219