Well, yeah… that’s what the errors mean — mdns isn’t working, so it won’t show up in iTunes.
But it’s not an mt-daapd thing per se, it looks like something specific to mdns.
If it can’t open a multicast socket, then it make sense to look for something broken networkingly.
1. What distro of linux?
2. What kernel version?
3. From distro-provided package, or hand-rolled?
4. If hand-rolled, did you enable multicast?
5. What kind of machine? Architecture type… AMD, Intel, 32bit, 64 bit, etc.
6. Is this machine multihomed? What kind of network interfaces does it have? 10/100 ethernet? Token ring? ATM?
7. Any IP aliases?
8. Any security patches? selinux? grsecurity? pax? lids? anything like that?
output of /sbin/ifconfig wouldn’t hurt, same with ‘uname -a’, and maybe the .config of the currently running kernel.
that’s where to check next.