Comment 14 for bug 1838038

Adding snap-core18 and snap-core20 tasks as it is a problem of core18 and core20 missing support for looking up host names via mDNS/DNS-SD. The problem occurs also in other Snaps not only in the Chromium Browser Snap. Therefore the fix for this bug is essentially important and urgently needed.

Note that installing nscd is only a workaround, which can cause security problems (aacording to Jamie Strandboge) when seeding it and also it would only help Ubuntu users.

Especially also the CUPS Snap (https://github.com/OpenPrinting/cups-snap) and Printer Application Snaps (the way to snap printer and scanner drivers, required for the CUPS Snap, currently, we have the PostScript Printer Application, https://github.com/OpenPrinting/ps-printer-app) are affected as they internally use mDNS .local addresses to access network devices. As we want to switch over printing in Ubuntu to the CUPS Snap and also want to give manufacturers a way to publish distribution-independent snapped printer/scanner drivers this problem needs to get urgently fixed.

A suggested fix can be found in this thread:

https://forum.snapcraft.io/t/no-mdns-support-in-snaps-should-core-have-a-modified-nsswitch-conf/

The /etc/nsswitch.conf file needs a simple change, replacing the line

hosts: files dns

by

hosts: files mdns4_minimal [NOTFOUND=return] dns

and the libnss-mdns package (provides libnss_mdns*.so*) needs to get installed into the coreXX images.