source: MondoRescue/branches/3.3/mindi-busybox/examples/var_service/dhcp_if_pinger/run

#!/bin/sh

# How often to test, seconds
ping_time=67
# "One ping, must have reply in 1 sec"
ping_opts="-c1 -W1 -w1"
# If ping failed, how soon to retry
retry_time=5
# Reinit after this many consecutive ping error
max_fail=5
# Interface whose DHCP data to use
if=${PWD##*/dhcp_}
if=${if%%_pinger}

msg() {
    echo "`date '+%Y-%m-%d %H:%M:%S'` $*" >>"$0.log"
}

if test -f "$0.log"; then
    tail -999 "$0.log" >"$0.log.new"
    mv "$0.log.new" "$0.log"
fi

test -f "/var/service/dhcp_$if/env.out" || exec env - sleep "$ping_time"

. "/var/service/dhcp_$if/env.out"
test x"$router" != x"" || exec env - sleep "$ping_time"

#msg "Pinging $router"
failcnt=0
while true; do
    ping $ping_opts "$router" && exec env - sleep "$ping_time"
    : $((failcnt++))
    msg "Failed to ping $router, fail count:$failcnt"
    test $failcnt -ge $max_fail && break
    env - sleep "$retry_time"
done

test -d "/var/service/dhcp_$if" && {
    msg "Restarting /var/service/dhcp_$if"
    sv t "/var/service/dhcp_$if"
}
test -d "/var/service/supplicant_$if" && {
    msg "Restarting /var/service/supplicant_$if"
    sv t "/var/service/supplicant_$if"
}
exec env - sleep "$ping_time"