#!/bin/bash
# Onno Zweers, juni 2008
#
# Description:
#
# This plugin checks if we're running the newest installed kernel.
# It has been tested on Centos 6 but should work on other RPM based distros too.
#
# 2013-01-31 - Onno - Created function compare_versions with improved logic.

# Nagios return codes
STATE_OK=0
STATE_WARNING=1
STATE_CRITICAL=2
STATE_UNKNOWN=3
STATE_DEPENDENT=4

CHECK_NAME="KERNEL"

PROGNAME=`basename $0`

# Check if grep supports --only-matching.
if ! grep --help | grep -- '--only-matching' &> /dev/null ; then
    echo "UNKNOWN - This version of grep does not support --only-matching."
    exit $STATE_UNKNOWN
fi

compare_versions() {
  # Put the version number in a bash list
  local version1=(`echo $1 | sed -e 's/[\.\-]/ /g' `)
  local version2=(`echo $3 | sed -e 's/[\.\-]/ /g' `)
  #echo "${version1[@]} ? ${version2[@]}"
  local operator="$2"
  EQUAL='=' ; FIRST_BIGGER='>' ; SECOND_BIGGER='<' 
  i=0
  # Check all elements of the version number, starting with the most significant
  while true ; do
    #echo "Comparing ${version1[$i]} and ${version2[$i]}"
    # Are we done checking?
    if [ -z "${version1[$i]}" -a -z "${version2[$i]}" ] ; then
      test "$operator" = "$EQUAL"
      return $?   # Return exit value of the previous test command
    fi
    # If one of the version numbers has less elements, assume zero.
    if [ -z "${version1[$i]}" ] ; then
      version1[$i]=0
    fi
    if [ -z "${version2[$i]}" ] ; then
      version2[$i]=0
    fi
    if [ "${version1[$i]//[_a-zA-Z]}" -gt "${version2[$i]//[_a-zA-Z]}" ] ; then
      test "$operator" = "$FIRST_BIGGER"
      return $?
    fi
    if [ "${version1[$i]//[_a-zA-Z]}" -lt "${version2[$i]//[_a-zA-Z]}" ] ; then
      test "$operator" = "$SECOND_BIGGER"
      return $?
    fi
    i=$((i + 1))
  done
}

RUNNING_KERNEL=`uname -r | sed 's/\.el[567].*//' | grep -o '[0-9].*[0-9]'`
INSTALLED_KERNELS=`rpm -qa | \
               grep '^kernel-\(lt-\)\{0,1\}[[:digit:]]' | \
               sed 's/\.x86_64.*//' | \
               sed 's/\.el[567].*//' | \
               grep -o '[0-9].*[0-9]' | \
               sort `

# Assume OK until proven not OK
running_kernel_is_the_latest=true
for INSTALLED_KERNEL in $INSTALLED_KERNELS ; do
  if compare_versions "$RUNNING_KERNEL" '<' "$INSTALLED_KERNEL" ; then
    running_kernel_is_the_latest=false
    NEWER_KERNELS="$NEWER_KERNELS $INSTALLED_KERNEL" 
  fi
done

if $running_kernel_is_the_latest ; then
    echo "OK - Running kernel: $RUNNING_KERNEL; available kernels: " $INSTALLED_KERNELS.
    exit $STATE_OK
else
    if [ "$1" = "--warn-only" ] ; then
        echo "$CHECK_NAME WARNING - Running kernel: $RUNNING_KERNEL but newer kernels available: $NEWER_KERNELS."
        exit $STATE_WARNING
    else
        echo "$CHECK_NAME CRITICAL - Running kernel: $RUNNING_KERNEL but newer kernels available: $NEWER_KERNELS."
        exit $STATE_CRITICAL
    fi
fi