连续4个小时ping不通远端主机，则本机关机

 #!/bin/bash

 #连续4个小时ping不通远端主机，则本机关机。

 begin_time=$(date "+%s")

 while true;do

     sleep 2

     ping -c 1 172.16.160.1 > /dev/null

     if [ $? != 0 ];then

         end_time=$(date "+%s")

     else

         begin_time=$(date "+%s")

     fi

     if [ $end_time -gt $begin_time ] ; then

         time_difference=$(($end_time - $begin_time))

         echo $time_difference

         if [ $time_difference -gt 14400 ]; then

         shutdown -h now

         fi

     fi

 done