/etc/avahi/services/nut.service is in nut-server 2.6.3-1ubuntu1.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | <?xml version="1.0" standalone='no'?><!--*-nxml-*-->
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<!--
  This file is part of NUT - Network UPS Tools
  NUT is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as
  published by the Free Software Foundation; either version 2 of the
  License, or (at your option) any later version.
  NUT is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.
  You should have received a copy of the GNU Lesser General Public
  License along with NUT; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  02111-1307 USA.
-->
<!-- See avahi.service(5) for more information about this configuration file -->
<service-group>
  <name replace-wildcards="yes">%h</name>
  <service>
    <type>_nut._tcp</type>
    <port>3493</port>
  </service>
</service-group>
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