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The above command will cause the ping-detect script to continuously ping the host at 192.168.22.2
which is the router. If the router crashes, it will no longer respond to ping requests. If this happens, the
two commands pmpower and date will run. The output from these commands is sent to the file
/tmp/output.log so that we have a record. The ping-detect is also run in the background using the "&".
Remember the rc.local script only runs by default when the system boots. You can manually run the
rc.local script or the ping-detect script if desired.
The ping-detect script
The above is just one example of using the ping-detect script. The idea of the script is to run any number
of commands when a specific host stops responding to ping requests. Here are details of the ping-detect
script itself:
#!/bin/sh
# Usage: ping-detect HOST [COMMANDS...]
# This script takes 2 types of arguments: hostname/IPaddress to ping, and the commands to
# run if the ping fails 5 times in a row. This script can only take one host/IPaddress per
# instance. Multiple independent commands can be sent to the script. The commands will be
# run one after the other.
#
# PINGREP is the entire reply from the ping command
# LOSS is the percentage loss from the ping command
# $1 must be the hostname/IPaddress of device to ping
# $2... must be the commands to run when the pings fail.
COUNTER=0
TARGET="$1"
shift
# loop indefinitely:
while true
do
# ping the device 10 times
PINGREP=`ping -c 10 -i 1 "$TARGET" `
#get the packet loss percentage
LOSS=`echo "$PINGREP" | grep "%" | sed -e 's/.* \([0-9]*\)% .*/\1/'`
if [ "$LOSS" -eq "100" ]
then
COUNTER=`expr $COUNTER + 1`
else
COUNTER=0
sleep 30s
fi
if [ "$COUNTER" -eq 5 ]
then
COUNTER=0
"$@"
sleep 2s
fi
done
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