keep alive script to ensure dhclient is running all the time

dhclient_keepalive.sh

#!/usr/bin/env bash

# This script should be run periodically to ensure that dhclient process is active.
pidfile_glob="/run/dhclient*"
regex="/run/dhclient\.([a-z]+[0-9]+)\.pid"
matched=0
function _logger() {
  logger "DHCLIENT KEEPALIVE: " $@
  echo "DHCLIENT KEEPALIVE: " $@
}
for f in $pidfile_glob
do
    if [[ $f =~ $regex ]]
    then
        matched=1
        interface="${BASH_REMATCH[1]}"
        procs=$(ps -ef | grep dhclient | grep $interface | grep -v grep)
        proc_count=$(echo "$procs" | wc -l)

        if [[ "$proc_count" -gt "1" ]]
        then
          kill -9 $(echo "$procs" | awk '{print $2}')
          procs=""
          _logger "Multiple processes found and killed. ${interface}"
        fi

        proc=$(echo "$procs" | head -n 1)
        pid="$(echo "$proc" | awk '{print $2}' )"
        fpid="$(cat /var/run/dhclient.$interface.pid)"
        if [[ "$pid" != "$fpid" ]]
        then
          _logger "PID mismatch: ${fpid}(${pid}) / ${interface}"
          if [[ "$fpid" == "" && "$pid" != "" ]]
          then
            kill -9 $pid
            _logger "PID Killed: ${pid} / ${interface}"
          fi
          if eval dhclient -1 -v -pf /run/dhclient.${interface}.pid -lf /var/lib/dhcp/dhclient.${interface}.leases ${interface}; then
            _logger "Started: $(cat /run/dhclient.${interface}.pid) / ${interface}"
            exit 0
          else
            _logger "Error starting dhclient: ${interface}"
            exit 1
          fi
        else
          echo "Process and pid match: ${proc}"
        fi
    fi
done

if [[ $matched == 0 ]]
then
  interface=eth0
  _logger "No run files matched. Starting on ${interface}"
  eval dhclient -1 -v -pf /run/dhclient.${interface}.pid -lf /var/lib/dhcp/dhclient.${interface}.leases ${interface}
fi