Using Munin Day to Day¶

This page covers the practical aspects of working with Munin once it is installed and collecting data.

Reading Graphs¶

Munin graphs show data over time. The default view shows the last 24 hours. You can switch between time ranges using the links at the top of each graph:

hour — last 60 minutes (5-minute resolution)
day — last 24 hours (5-minute resolution)
week — last 7 days (30-minute resolution)
month — last 31 days (2-hour resolution)
year — last 12 days (1-day resolution)

Understanding Graph Types¶

Counter / Derive graphs (network traffic, disk I/O)

These show rates — bytes per second, operations per second, etc. The Y-axis label says “per second” or “per minute” depending on the graph_period setting. Values represent the rate of change since the last measurement.

If you see a flat line at zero, the counter may have been reset or the data type may be wrong. If you see sudden spikes, the counter may have wrapped or been reset.

Gauge graphs (temperature, load, disk usage)

These show absolute values — degrees, percentage, number of processes. The Y-axis label shows the unit directly.

If you see NaN (not a number), the plugin may have failed to produce a value, or RRDtool does not have enough data points yet.

Stacked graphs (disk usage by partition, traffic by interface)

Multiple data sources are stacked on top of each other. The total height represents the sum. Click on a graph to see the individual components.

Understanding Colors¶

Green — normal values within thresholds
Yellow — values above the warning threshold
Red — values above the critical threshold
Grey — unknown or missing data

The warning and critical thresholds are set by the plugin or overridden in munin.conf. See Let Munin croak alarm for details.

Working with Thresholds¶

Munin plugins define default warning and critical thresholds. You can override these in /etc/munin/munin.conf on the master.

Setting Thresholds¶

To set a warning level for a specific data source on a specific host:

[webserver.example.com]
  address 192.0.2.10
  cpu.user.warning 80
  cpu.user.critical 95

This sets a warning at 80% and critical at 95% for the user field of the cpu plugin on webserver.example.com.

To set thresholds for all hosts in a group:

[webservers;]
  cpu.user.warning 80

Threshold Syntax¶

A single number sets the upper limit:

cpu.user.warning 80

A colon-separated pair defines a range. Values outside the range trigger the alert:

cpu.user.warning 20:80

This warns when the value is below 20 or above 80.

Checking Current Thresholds¶

To see what thresholds are currently set for a plugin:

sudo munin-run cpu config

Look for lines like cpu.user.warning and cpu.user.critical.

Managing Nodes¶

Adding a New Node¶

Install munin-node on the new machine.
Edit /etc/munin/munin-node.conf on the new node and add the master’s IP to the allow list.
Restart munin-node on the new machine.
Add a section for the new node in /etc/munin/munin.conf on the master:
```
[newserver.example.com]
  address 192.0.2.20
```
Wait for the next munin-cron run (up to 5 minutes), or run it manually:
```
sudo -u munin /usr/share/munin/munin-cron
```

Removing a Node¶

Remove or comment out the node’s section in /etc/munin/munin.conf.
The RRD files in /var/lib/munin/ are not automatically removed. You can delete them manually if desired.
Optionally uninstall munin-node from the removed machine.

Organizing with Groups¶

Munin uses groups to organize nodes in the web interface. Groups are defined by the hierarchy in munin.conf:

[dc1;web;web1.example.com]
  address 192.0.2.10

[dc1;web;web2.example.com]
  address 192.0.2.11

[dc1;db;db1.example.com]
  address 192.0.2.20

This creates a hierarchy: dc1 → web → web1, dc1 → db → db1.

If you use a simple hostname without a semicolon, the domain part becomes the group:

[web1.example.com]
  address 192.0.2.10

This places web1.example.com in the group example.com.

Adding Plugins¶

Installing a Plugin¶

Place the plugin script in /usr/share/munin/plugins/ (or any directory you prefer).

Make it executable:

chmod +x /usr/share/munin/plugins/myplugin

Create a symlink in /etc/munin/plugins/:

ln -s /usr/share/munin/plugins/myplugin /etc/munin/plugins/myplugin

Restart munin-node:
```
sudo systemctl restart munin-node
```

Test the plugin:

sudo munin-run myplugin
sudo munin-run myplugin config

Using Wildcard Plugins¶

Wildcard plugins monitor multiple instances of the same thing (network interfaces, disk drives, etc.). They use the symlink name to determine what to monitor.

For example, the if_ plugin monitors network interfaces:

ln -s /usr/share/munin/plugins/if_ /etc/munin/plugins/if_eth0
ln -s /usr/share/munin/plugins/if_ /etc/munin/plugins/if_eth1

See Wildcard Plugins for details.

Configuring Plugin Environment¶

Some plugins need environment variables (database credentials, SNMP communities, etc.). Set these in /etc/munin/plugin-conf.d/:

[myplugin]
  env.DB_HOST localhost
  env.DB_USER munin
  env.DB_PASS secret

See Configuring for the full configuration reference.

Checking Munin’s Health¶

Log Files¶

Munin writes logs to /var/log/munin/:

munin-update.log — data collection from nodes
munin-limits.log — threshold checks and alerts
munin-httpd.log — web interface requests (if logging is enabled)

Check these logs if something is not working as expected.

Quick Health Check¶

Run this to verify the master can reach a node and collect data:

sudo -u munin /usr/share/munin/munin-update --debug --nofork --host <node-address> --service <plugin-name>

This shows the full communication between master and node.

Verifying Data Collection¶

To check that data is being written to RRD files:

rrdtool fetch /var/lib/munin/<domain>/<host>-<plugin>-<field>-g.rrd AVERAGE | tail -5

This shows the last 5 data points for the specified field.