Checking for the latest kernel with Nagios

I’ve just written a module for Nagios that will determine if the currently running kernel is the latest kernel available on the system. It will not tell you if there is a newer kernel in a yum repository or similar.

The main gotcha is that you need an RPM-based system for my script to work, e.g. RHEL, CentOS, Fedora and many others. It is most certainly not bulletproof, but it works on my systems.

All feedback welcome.

N.B. I’ve now published this module on Monitoring Exchange. Please download the plugin from there, as I will keep that copy up to date if there are changes in the future (and the copy on this page is likely to go out of date).

check_kernel

#!/usr/bin/perl -w

# Usage:   check_kernel

use strict;
use lib "/usr/local/nagios/libexec";
use utils qw(%ERRORS);

my $running_kernel=`uname -r`;
my $installed_kernel=`rpm -q kernel | tail -n 1`;
my $rpm = `which rpm`;

chomp $running_kernel;
chomp $installed_kernel;

if ($rpm =~ m/no rpm in/i) {
   print "UNKNOWN - You must be running an RPM-based systemn";
   exit $ERRORS{'UNKNOWN'};
}

if (!defined $running_kernel || !defined $installed_kernel) {
   print "UNKNOWN - Test failedn";
   exit $ERRORS{'UNKNOWN'};
}

# Strip off the "kernel-" prefix so the strings will match
$installed_kernel =~ s/kernel-//gi;

# Do the test
if ($running_kernel eq $installed_kernel) {
   print "OK - running latest installed kernel ($running_kernel)n";
   exit $ERRORS{'OK'};
} else {
   print "WARNING - reboot to run latest installed kernel ($installed_kernel)n";
   exit $ERRORS{'WARNING'};
}

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