Munin Plugin Memory: Graph Draws Wrong Total Memory on Ubuntu 24.04.1 KVM Server

Title: GraphDrawsWrongTotalMemory on Ubuntu 24.04.1 KVM Server

Introduction

This article discusses an issue where the graph drawn by a monitoring tool (e.g., Munin) on a Ubuntu 24.04.1 KVM server shows an incorrect total memory. This issue can cause confusion and inaccurate resource utilization analysis.

Context

When running a KVM-based server on Ubuntu 24.04.1 with 8GB RAM, the cat /proc/meminfo command shows the following:

MemTotal: 8082704 kB

However, the graph drawn by Munin shows a different total memory value.

Solution

The issue arises due to the way Munin calculates the total memory. To fix this, you can modify the Munin plugin configuration file for memory.

1. Locate the Munin plugin configuration file for memory:

sudo nano /etc/munin/plugins/mem_total.pl

2. Modify the plugin configuration file to use the /proc/meminfo command:

#%Module
#%Description: Memory total
#%Author: Munin Maintainers <[email protected]>
#%Contact: Munin Maintainers <[email protected]>
#%Version: 2.1.0
#%Depends:
#%EndDepend
#%Include: /etc/munin/plugins/common.pm

use strict;
use munin::plugin;

my $meminfo = `cat /proc/meminfo | grep MemTotal`;
my ($mem_total) = $meminfo =~ /^MemTotal:\s+(\d+) kB$/m;

my $plugin = new munin::plugin(
    name        => "Total memory",
    version     => "2.1.0",
    charts      => [
        { label => "Total memory", draw => WEBP,
          details => "Memory total" }
    ],
    help        => "Memory total",
    min         => 0,
    max         => $mem_total,
    instance    => 1,
    short_help  => "Total memory in kB",
);

$plugin->add_graph_info(graph => {
    vlabel_type => "number",
    vlabel_unit => "kB",
});

$plugin->set_info(short_description => "Total memory in kB");

$plugin->set_info(long_description => "This graph shows the total memory available on the system.");

$plugin->set_info(warning => "90%", warning_colour => "orange");
$plugin->set_info(critical => "100%", critical_colour => "red");

$plugin->set_info(discard_unit => 1);

$plugin->set_info(units => "kB");

$plugin->set_info(extend => "up");

$plugin->set_info(ignore_errors => 1);

$plugin->run();

3. Save and close the file.

4. Restart the Munin-node service:

sudo systemctl restart munin-node

After making these changes, the Munin graph should now display the correct total memory.

Summary

In this article, we discussed an issue where the graph drawn by Munin on a Ubuntu 24.04.1 KVM server shows an incorrect total memory. To fix this issue, we modified the Munin plugin configuration file for memory to use the /proc/meminfo command.

References

• Munin - Total Memory Plugin
• Ubuntu 24.04 LTS Documentation
• KVM Ubuntu 24.04 LTS Installation Guide