/etc/network/if-up.d/epoptes-client is in epoptes-client 0.5.10-2.
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 | #!/bin/sh
# Don't do anything for the lo interface
test "$IFACE" != lo || exit 0
# Only run from ifup
test "$MODE" = start || exit 0
# Only care about inet, inet6 and NetworkManager
case "$ADDRFAM" in
    inet|inet6|NetworkManager)
        ;;
    *)
        exit 0
esac
if [ -x /usr/bin/logger ]; then
    logger=logger
else
    logger=true
fi
$logger -t epoptes -p syslog.info "Running epoptes-client, IFACE=$IFACE, pid=$$"
if [ -x /sbin/ethtool ] && [ -f /etc/default/epoptes-client ]; then
    . /etc/default/epoptes-client
    if [ -n "$WOL" ]; then
        # $WOL is unquoted in case someone wants to add sopass
        ethtool -s "$IFACE" wol $WOL
    fi
fi
/usr/sbin/epoptes-client &
 |