/etc/isdn/stop is in isdnlog 1:3.25+dfsg1-3.3ubuntu2.
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 50 51 52 53 | #!/bin/sh
# Very simple reload default for the chargemax feature of isdnlog.
# This is called by isdnlog every time we get a AOCD and chargesum of
# active device is greater than CHARGEMAX.
# there are three parameters available:
#
#  first ($1) is chargesum-CHARGEMAX
# second ($2) is ALIAS as defined in ISDNLOG.CONF
#  third ($3) is total chargesum for active device
msg=`tempfile -p isdn`
myecho() {
    echo "$@" >> $msg
}
case "$1" in
5\.*)
        myecho "WARNING, charge-limit set by CHARGEMAX is reached!"
        myecho "$2 is talking too much!"
#        /bin/play /usr/sounds/attention.au
        ;;
10\.* | 11\.* )
        myecho "WARNING, $2 got charge-overflow == $1, total chargesum == $3"
        myecho "next chargeint will cause i4l to stop"
#        /bin/play /usr/sounds/earthdestruction.au
        ;;
20\.* | 21\.* )
        myecho "reload got charge-overflow == $1, now ipppd will be stopped!"
        /sbin/init.d/isdnutils stop ipppd
        ;;
25\.* | 26\.* )
#        echo "aeh, still alive?! so we'll do a reboot!!" >> /dev/console
#        /bin/play /usr/sounds/crash.au
#        /sbin/reboot
        myecho "still alive?! Stopping ISDN subsystem!"
        /usr/sbin/isdnctrl system off
        ;;
esac
myecho "got charge_ov=$1 dev=$2 scharge=$3 "
if [ -s "$msg" ]; then
    logger -f $msg -p daemon.notice -t isdnlog
    cat $msg >> /dev/console
fi
rm -f $msg
exit 0
 |