Monitor IPS uptime by pinging an external IP

down.sh

#!/bin/bash
#
# Ping external IP from wired network to monitor for ISP outtage
# 2020-06-16
#
# runs on pi-hole from cron every day
#
# kill any other instances running
# name log file day_of_month_down.txt
# remove todays log file if there is one, since it will be a month old
#
# run `ping -c 1 -t 2 8.8.8.8` in a loop, check exit code, if > 0, append log file with "2020-06-16 12:34:56 down" then sleep 1

OS=$(uname)
SCRIPT=$(basename "$0")
DAY_OF_MONTH=$(date +%d)
LOG_FILE="${DAY_OF_MONTH}_down.txt"
EXTERNAL_IP="8.8.8.8"
# EXTERNAL_IP="10.10.10.10"
TIMEOUT_FLAG="-W"

# ping uses a different flag for timeout on macOS
if [ "${OS}" == "Darwin" ]
then
  TIMEOUT_FLAG="-t"
fi

# kill any other instances that are at least 1 second old
if [ "${OS}" == "Linux" ]
then
  KILL=$(killall -q -o 1s ${SCRIPT})
fi

# clean up old log file
CLEANUP=$(rm -f ${LOG_FILE})

# run until day changes
# script will get killed by next day's script anyway
while [ "$DAY_OF_MONTH" == "$(date +%d)" ]
do
  # ping quiet mode, one time, for a max of one second
  CMD="ping -q -c 1 ${TIMEOUT_FLAG} 1 ${EXTERNAL_IP}"
  # run the command
  $CMD
  # exit status
  STATUS=$?

  # internet is probably down if we can't ping out
  if [ "$STATUS" -gt "0" ]
  then
    TIMESTAMP=$(date "+%Y-%m-%d %H:%M:%S")
    LOG=$(echo "${TIMESTAMP} down" >> ${LOG_FILE})
  fi

  sleep 1
done