/etc/cfengine/debian-edu/cf.nagios3 is in debian-edu-config 1.818+deb8u2.
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 | #links:
#
#    /etc/nagios3/cgi.cfg ->! /etc/nagios3/debian-edu/cgi.cfg
#    /etc/nagios3/nagios.cfg ->! /etc/nagios3/debian-edu/nagios.cfg
#    /etc/nagios3/htpasswd.users ->! /etc/nagios3/debian-edu/htpasswd.users
#    /etc/nagios3/conf.d ->! /etc/nagios3/debian-edu
#
files:
  debian.server.installation::
    # create an empty web site password file to allow htpasswd to add
    # users to it.
    # TODO: This file should have mode 0640 and be owned by the same group
    # the web server runs as, but I will not change this close to release.
    # 20100121, werner
    /etc/nagios3/htpasswd.users owner=root group=root mode=644 act=touch
# Workaround for a variant of bug #760084 triggered by #483997,
# apt/dpkg do not order recommends and suggests, causing sitesummary
# to be installed before nagios3, and thus failing to configure
# nagios3 properly.
shellcommands:
  debian.fifthpass::
    "/usr/sbin/dpkg-reconfigure sitesummary"
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