postinst is in nagios3-cgi 3.5.1-1ubuntu1.3.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
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 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 | #!/bin/bash
set -e
# some shorthands for sanity
en="/etc/nagios3"
enc="/etc/nagios3/conf.d"
usn="/usr/share/nagios3"
. /usr/share/debconf/confmodule
if [ -n "$NAG3DEBUG" ]; then
  echo "now debugging $0 $@"
  set -x
fi
# location of the default apache configuration for nagios.
apacheconf=$en/apache2.conf
# location of the default htpasswd authentication file.
htpw=$en/htpasswd.users
setperm() {
    local user="$1"
    local group="$2"
    local mode="$3"
    local file="$4"
    shift 4
    # only do something when no setting exists
    if ! dpkg-statoverride --list "$file" >/dev/null 2>&1; then
      chown "$user":"$group" "$file"
      chmod "$mode" "$file"
    fi
}
case "$1" in
  configure)
    if ! getent passwd nagios > /dev/null ; then
      echo 'Adding system-user for nagios' 1>&2
      adduser --system --group --home /var/lib/nagios \
              --disabled-login --force-badname nagios > /dev/null
    fi
	db_get nagios3/adminpassword
	admpass="$RET"
	# register apache2.conf via ucf:
	ucf --debconf-ok /usr/share/nagios3-cgi/apache2.conf $apacheconf
   echo "enabling Apache2 config..."
   COMMON_STATE=$(dpkg-query -f '${Status}' -W 'apache2.2-common' 2>/dev/null | awk '{print $3}' || true)
   # NEW method for Apache >= 2.4
   if [ -e /usr/share/apache2/apache2-maintscript-helper ]; then
       . /usr/share/apache2/apache2-maintscript-helper
       apache2_invoke enmod cgi
       apache2_invoke enconf nagios3
       # remove OLD Apache 2.2 link
       [ -L /etc/apache2/conf.d/nagios3.conf ] && rm /etc/apache2/conf.d/nagios3.conf
       # OLD methods for Apache < 2.4
   elif [ "$COMMON_STATE" = "installed" ] || [ "$COMMON_STATE" = "unpacked" ] ; then
       # create symlink if not existing
       [ -f /etc/apache2/conf.d/nagios3.conf ] || ln -vs $apacheconf /etc/apache2/conf.d/nagios3.conf
       # reload webserver
       [ -x $(which invoke-rc.d) ] && invoke-rc.d apache2 reload
   fi
	# we reset the password every run, so if it exists we're running
	# after being specifically given a password and can unconditionally set it.
	# XXX there's no way of setting the pw w/out giving it on the cmdline? wtf?
	if [ -n "$admpass" ]; then
		touch "$htpw"
		htpasswd -b "$htpw" nagiosadmin "$admpass"
	fi
	# everything went well, so now let's reset the password
	db_set nagios3/adminpassword ""
	db_set nagios3/adminpassword-repeat ""
	# ... done with debconf here
	db_stop
    ;;
  abort-upgrade|abort-remove|abort-deconfigure)
    ;;
  *)
    echo "postinst called with unknown argument \$1'" >&2
    exit 1
    ;;
esac
 |