monitoring/check_dns.sh

#!/usr/bin/env bash

check_string_ps=""
if [[ -f "/usr/sbin/named" ]] ; then
	check_string_ps="/usr/sbin/named"
fi

check_file="/tmp/dns-check-failed"

alternate_addr="oopen.de google.com heise.de debian.org ubuntu.com"


# - used, if systemd is NOT supported
bind_init_script=""
if [[ -x "/etc/init.d/bind9" ]] ; then
   bind_init_script="/etc/init.d/bind9"
fi

# - Used if systemd is supported
# -
service_name=bind9

LOCK_DIR="/tmp/$(basename $0).$$.LOCK"


#---------------------------------------
#-----------------------------
# Base Function(s)
#-----------------------------
#---------------------------------------

clean_up() {

   # Perform program exit housekeeping
   rm -rf "$LOCK_DIR"
   blank_line
   exit $1
}

fatal(){
   echo ""
   if $terminal ; then
      echo -e "   [ \033[31m\033[1mFatal\033[m ] $*"
   else
      echo -e "   [ Fatal ] $*"
   fi
   echo ""
   if $terminal ; then
      echo -e "             \033[1mScript terminated\033[m.."
   else
      echo -e "             Script terminated.."
   fi
   echo ""
   rm -rf $LOCK_DIR
   exit 1
}

error (){
   echo ""
   if $terminal ; then
      echo -e "   [ \033[31m\033[1mError\033[m ] $*"
   else
      echo "   [ Error ] $*"
   fi
   echo ""
}

warn (){
   echo ""
   if $terminal ; then
      echo -e "   [ \033[33m\033[1mWarn\033[m ]  $*"
   else
      echo "   [ Warn ]  $*"
   fi
   echo ""
}

info (){
   echo ""
   if $terminal ; then
      echo -e "   [ \033[32m\033[1mInfo\033[m ]  $*"
   else
      echo "   [ Info ]  $*"
   fi
   echo ""
}

ok (){
   echo ""
   if $terminal ; then
      echo -e "   [ \033[32m\033[1mOk\033[m ]    $*"
   else
      echo "   [ Ok ]    $*"
   fi
   echo ""
}

trim() {
    local var="$*"
    var="${var#"${var%%[![:space:]]*}"}"   # remove leading whitespace characters
    var="${var%"${var##*[![:space:]]}"}"   # remove trailing whitespace characters
    echo -n "$var"
}

blank_line() {
   if $terminal ; then
      echo ""
   fi
}


## - Test of valid IPv4 Address
## -
## -    Returns 0 if valid, > 0 otherwise
## -
is_valid_ipv4() {
  local -a octets=( ${1//\./ } )
  local RETURNVALUE=0

  # return an error if the IP doesn't have exactly 4 octets
  [[ ${#octets[@]} -ne 4 ]] && return 1

  for octet in ${octets[@]}
  do
    if [[ ${octet} =~ ^[0-9]{1,3}$ ]]
    then # shift number by 8 bits, anything larger than 255 will be > 0
      ((RETURNVALUE += octet>>8 ))
    else # octet wasn't numeric, return error
      return 1
    fi
  done
  return ${RETURNVALUE}
}


# ----------
# - Jobhandling
# ----------

# - Run 'clean_up' for signals SIGHUP SIGINT SIGTERM
# -
trap clean_up SIGHUP SIGINT SIGTERM

# - Create lock directory '$LOCK_DIR"
#
mkdir "$LOCK_DIR"



# ----------
# - Some checks
# ----------


# - Running in a terminal?
# -
if [[ -t 1 ]] ; then
   terminal=true
   LOGGING=true
else
   terminal=false
   LOGGING=false
fi

if [[ -z $check_string_ps ]]; then
   fatal "$(basename $0): Bind Nameservice seems NOT to be installed"
fi

# - Systemd supported ?
# -
systemd=$(which systemd)
systemctl=$(which systemctl)

systemd_supported=false
if [[ -n "$systemd" ]] && [[ -n "$systemctl" ]] ; then
   systemd_supported=true
else
   if [[ ! -x $bind_init_script ]]; then
      fatal "$(basename $0): Missing Bind Init-Script!"
   fi
fi


#---------------------------------------
#-----------------------------
# Check if Bind Nameservice is running
#-----------------------------
#---------------------------------------

if $LOGGING ; then
   echo -e "\n   Check if Bind Nameservice is running.."
   echo -e "   ======================================"
fi

for host in $alternate_addr  ; do

   ip_addr="$(dig +short $host 2> /dev/null)"

   #if [[ $? -eq 0 ]] && [[ -n "$ip_addr" ]] ; then 
   if [[ $? -eq 0 ]] && is_valid_ipv4 $ip_addr ; then 
      if $LOGGING ; then
         ok "Bind Nameservice is up and running."
      fi
      if [[ -f "$check_file" ]]; then
         rm -f "$check_file" > /dev/null 2>&1
      fi
      clean_up 0
   fi

done;

if [[ ! -f "$check_file" ]] ; then
   touch /tmp/dns-check-failed
   if $LOGGING ; then
      warn "There was no correct answer from the 'bind' name service.

             This time i will go on, but if next time the bind service still answers 
             incorrect, i'll do something."
   fi
   clean_up 1
fi

PID=$(ps -e f | grep -E "[[:digit:]]\ ${check_string_ps}"| grep -v grep | awk '{print$2}')
if [[ "X${PID}" = "X" ]]; then

   error "Bind Nameservice seems to be down! Trying to restart service now.."

else

   error "A \"named\" process is running, but bind service did no answer in a correct way.

             ** Probably you have a network problem **
             
             What the heck: I restart the bind9 service anyway - Maybe that will help."
fi

if $systemd_supported ; then
   $systemctl stop $service_name > /dev/null 2> ${LOCK_DIR}/err_msg.log
   if [[ $? -ne 0 ]]; then
      error "$(cat ${LOCK_DIR}/err_msg.log)"
   fi
   sleep 10
   $systemctl start $service_name > /dev/null 2> ${LOCK_DIR}/err_msg.log
   if [[ $? -ne 0 ]]; then
      error "$(cat ${LOCK_DIR}/err_msg.log)"
   fi
else
   $bind_init_script stop > /dev/null 2>&1
   if [[ $? -ne 0 ]]; then
      error "Stopping Bind Nameservice failed!"
   fi
   sleep 10
   $bind_init_script start > /dev/null 2>&1
   if [[ $? -ne 0 ]]; then
      error "Starting Bind Nameservice failed!"
   fi
fi

declare -i counter=0
PID=$(ps -e f | grep -E "[[:digit:]]\ ${check_string_ps}"| grep -v grep | awk '{print$2}')
while [[ "X${PID}" = "X" ]]; do
   sleep 1
   PID=$(ps -e f | grep -E "[[:digit:]]\ ${check_string_ps}"| grep -v grep | awk '{print$2}')
   if [[ $counter -gt 10 ]]; then
      break
   else
      ((counter++))
   fi
done

if [[ "X${PID}" = "X" ]] ; then
   error "Restarting Bind Nameservice failed!"
   clean_up 1
else
   ok "Bind Nameservice is up and running."
fi

   
clean_up 0;