/etc/needrestart/notify.d/300-needrestart-session is in needrestart-session 0.3-2.
This file is owned by root:root, with mode 0o755.
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  | #!/bin/sh
# needrestart-session - check for processes need to be restarted in user sessions
#
# Authors:
#   Thomas Liske <thomas@fiasko-nw.net>
#
# Copyright Holder:
#   2014 - 2015 (C) Thomas Liske [http://fiasko-nw.net/~thomas/]
#
# License:
#   This program is free software; you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation; either version 2 of the License, or
#   (at your option) any later version.
#
# Use dbus-send to launch needrestart-session in the user's session.
DBSEND='/usr/bin/dbus-send'
test -x "$DBSEND" || exit 1
case "$NR_SESSION" in
    session*)
	if [ -z "$(ps -Awwo uid,cmd -u "$NR_UID" --no-headers | grep needrestart-dbus-session)" ]; then
 	    echo "[$0] could not find a running needrestart-dbus-session for $NR_USERNAME" 1>&2
	    exit 1
	fi
 	echo "[$0] notify user $NR_USERNAME by needrestart-session" 1>&2
	# dbus-send fails if fd 1 is n/a
	if [ -e "/proc/$$/fd/2" ]; then
	    exec "$DBSEND" --system --print-reply --type=method_call \
		 --dest=net.ibh.NeedRestart.System \
		 /net/ibh/NeedRestart/System \
		 net.ibh.NeedRestart.System.emitNotifySessions 1>&2
	else
	    exec "$DBSEND" --system --print-reply --type=method_call \
		 --dest=net.ibh.NeedRestart.System \
		 /net/ibh/NeedRestart/System \
		 net.ibh.NeedRestart.System.emitNotifySessions 1> /dev/null
	fi
	;;
    *)
 	echo "[$0] skip session '$NR_SESSION'" 1>&2
	exit 1;
	;;
esac
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