/etc/default/avahi-daemon is in avahi-daemon 0.6.31-4ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # 1 = Try to detect unicast dns servers that serve .local and disable avahi in
# that case, 0 = Don't try to detect .local unicast dns servers, can cause
# troubles on misconfigured networks
AVAHI_DAEMON_DETECT_LOCAL=1
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