/etc/network/ip-down.d/51guidedog is in guidedog 1.3.0-1.
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 | #!/bin/sh
# If we are being called by ifupdown when it changes a PPP interface,
# and if the appropriate file is in place to do this for PPP anyway,
# don't do anything.
[ -x /etc/ppp/ip-up.d/51guidedog -a "$MODE" = "start" -a "$METHOD" = "ppp" ] && exit 0
[ -x /etc/ppp/ip-down.d/51guidedog -a "$MODE" = "stop" -a "$METHOD" = "ppp" ] && exit 0
# setup guidedog
if [ -x /etc/rc.guidedog ]; then
/bin/sh /etc/rc.guidedog
fi
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