Munin

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Munin is a networked resource monitoring tool that can help analyze resource trends and bottlenecks. Munin has a master/node architecture in which the master regularly fetches the data from the nodes and presents the information in graphs through a web interface. A default installation provides a lot of graphs with almost no work and new graphs can be easily created added as plugins. [1]

You can check out OpenStreetMap's Munin install for an example.

Installation

Install the munin package on the master machine and munin-node on the devices that you whish to monitor.

You can also install them both on the same machine so that the master machine monitors itself.

Further documentation may be found on the Munin documentation wiki.

Configuration

Munin master

Directories

Create a directory where the munin-master will write the generated HTML and graph images. The munin user must have write permission to this directory.

The following example uses /srv/http/munin, so the generated output can be viewed at http://localhost/munin/, provided that a web server is installed and running:

# mkdir /srv/http/munin
# chown munin:munin /srv/http/munin

Uncomment the htmldir entry in /etc/munin/munin.conf and change it to the directory created in the previous step:

htmldir /srv/http/munin

Cron

crontab

Run the following to have Munin collect data and update the generated HTML and graph images every 5 minutes:

# crontab /etc/munin/munin-cron-entry -u munin

Configure the email server to send mails to the munin user. If using postfix, add the following:

/etc/postfix/aliases

munin:    root

And run:

# newaliases

systemd timer

Instead of a cron job a systemd timer can be used.

This needs a service unit configuration:

/etc/systemd/system/munin-cron.service

[Unit]
Description=Survey monitored computers
After=network.target

[Service]
User=munin
ExecStart=/usr/bin/munin-cron

And a timer unit configuration:

/etc/systemd/system/munin-cron.timer

[Unit]
Description=Survey monitored computers every five minutes

[Timer]
OnCalendar=*-*-* *:00/5:00

[Install]
WantedBy=multi-user.target

Now, reload systemd configuration, enable and start munin-cron.timer

# systemctl daemon-reload
# systemctl enable --now munin-cron.timer

and verify that everything is working:

# journalctl --unit munin-cron.service
# less /var/log/munin/munin-update.log

Permissions

When graph_strategy cgi is enabled in /etc/munin/munin.conf ensure the directory /var/lib/munin/cgi-tmp is owned by user and group munin so that the /usr/share/munin/cgi/munin-cgi-graph script is able to write the png files to this directory.

# chown munin: /var/lib/munin/cgi-tmp

Testing

Once munin-cron is configured to run Munin will be ready to start generating graphs. Ensure the munin-node.service is running on each of the nodes. It may be useful to jump ahead to the #Munin node section and return here once the node are up and running.

Change to the munin user with the following su command, the -s/--shell option is for specifiying the shell (in this case bash). This needs to be done from root shell, since the munin user does not have a password:

# su -s /bin/bash munin

By runnning the munin-cron command manually it will trigger the generation of HTML and graph images immediately without having to wait for the next cron run:

munin> munin-cron

If the munin logging is configured, the logs are usually found in /var/log/munin/. Watching the munin-update.log log in a seperate terminal after running the munin-cron command can be helpful in diagnosing issues.

# tail -f /var/log/munin/munin-update.log

And finally test the interface by pointing your browser to the output directory or http://localhost/munin/.

Note: It might take a while for the graphs to have data, so be patient. Wait for about 30 minutes to an hour.

Munin node

Daemon

On the nodes, start and enable munin-node.

# systemctl enable --now munin-node

IPv6

For IPv6 support on munin-node, using:

/etc/munin/munin-node.conf

host :::1

Install:

Customization

Before running munin, you might want to setup the hostname of your system. In /etc/munin/munin.conf, the default hostname is myhostname. This can be altered to any preferred hostname. The hostname will be used to group and name the .rrd files in /var/lib/munin and further, used to group the html files and graphs in your selected munin-master directory.

Plugins

Run munin-node-configure with the --suggest option to have Munin suggest plugins it thinks will work on your installation:

# munin-node-configure --suggest

If there is a suggestion for a plugin you want to use, follow that suggestion and run the command again. When you are satisfied with the plugins suggested by munin-node-configure, run it with the --shell option to have the plugins configured:

# munin-node-configure --shell | sh

Adding

Basically all plugins are added in the following manner (although there are exceptions, review each plugin!):

Download a plugin, then copy or move it to /usr/lib/munin/plugins:

# cp plugin /usr/lib/munin/plugins/

Then link the plugin to /etc/munin/plugins:

# ln -s /usr/lib/munin/plugins/plugin /etc/munin/plugins/

Note: Some plugins - known as wildcard plugins - can be used with multiple devices at once by linking them with different names. These plugins end with an underscore and are linked as <plugin>_<device> to be used on <device>. See the if_ plugin for an example.

Now test your plugin. You do not need to use the full path to the plugin, munin-run should be able to figure it out:

# munin-run plugin

And restart munin-node.service. Finally, refresh the web page.

Additional plugins

There are many Munin plugins out there just waiting to be installed. The MuninExchange is an excellent place to start looking, and if you cannot find a plugin that does what you want it is easy to write your own. Have a look at Developing Plugins at the Munin documentation wiki to learn how.

Removing

If you want to remove a plugin, simply delete the linked file in /etc/munin/plugins - there is no need to remove the plugin from /usr/lib/munin/plugins.

# rm /etc/munin/plugins/plugin

Debugging

If you come across a plugin that is not working as expected (for example giving you no output at all) it might be interesting to run it directly. Fortunately there is a way to do this. Following the instructions until here, you will for example notice, that the plugin apache_accesses gives no output at all, when enabled. In order to run the plugin directly:

# munin-run apache_accesses

The following error:

LWP::UserAgent not found at /etc/munin/plugins/apache_accesses line 86.

indicates that a perl function could not be found. To resolve the problem, install the missing library, in this case, perl-libwww.

Permissions

Because many plugins read log files, it is useful to add munin user into log group:

# usermod -a -G log munin

Web server (optional)

This guide sets up Munin to generate static HTML and graph images and write them in a directory of your choosing. You can view these generated files locally with any web browser. If you want to view the generated files from a remote machine, then you will need to install and configure one of the following web servers:

Or one of the other servers found in the web server category.

Apache

Apache VirtualHost examples

Based on information found here:

In the next major release of Munin, things will be much simpler. Check it out:

https://web.archive.org/web/20180128051736/http://guide.munin-monitoring.org/en/latest/example/webserver/apache-virtualhost.html

Basic static HTML

<VirtualHost *:80>
    ServerName localhost
    ServerAdmin  root@localhost

    DocumentRoot /srv/http/munin

    ErrorLog /var/log/httpd/munin-error.log
    CustomLog /var/log/httpd/munin-access.log combined
</VirtualHost>

Static HTML with DynaZoom feature

Install perl-cgi-fast.

You must enable one of these:

mod_cgid (or mod_cgi if using mpm_prefork_module) by uncommenting the line in httpd.conf.
Or install mod_fcgid and add LoadModule fcgid_module modules/mod_fcgid.so in httpd.conf.

<VirtualHost *:80>
   ServerName localhost
   ServerAdmin  root@localhost

   DocumentRoot /srv/http/munin

   ErrorLog /var/log/httpd/munin-error.log
   CustomLog /var/log/httpd/munin-access.log combined

   # Rewrites
   RewriteEngine On

   # Images
   RewriteRule ^/munin-cgi(.*) /usr/share/munin/cgi/$1 [L] 

   # Ensure we can run (fast)cgi scripts
   <Directory "/usr/share/munin/cgi">
       Require all granted
       Options +ExecCGI
       <IfModule mod_fcgid.c>
           SetHandler fcgid-script
       </IfModule>
       <IfModule !mod_fcgid.c>
           SetHandler cgi-script
       </IfModule>
   </Directory>
</VirtualHost>

DynaZoom Permissions

When Munin cannot draw graphs and logs a similar message to Could not draw graph "/var/lib/munin/cgi-tmp/munin-cgi-graph/" check to make sure group permissions are set on /var/lib/munin/cgi-tmp/munin-cgi-graph/ so the munin-cgi-graph directory has writeable group permissions such as drwxrwxr-x 3 munin http 4096 Aug 9 20:11 munin-cgi-graph.

ls -l /var/lib/munin/cgi-tmp/

If group permissions are not set, then

chmod g+w /var/lib/munin/cgi-tmp/munin-cgi-graph/

Full dynamic

Use this VirtualHost if you want to set html_strategy and graph_strategy to cgi. Page loads will take longer because all the HTML and PNG files will be dynamically generated, but the munin-cron run will take less time because it will not execute munin-html and munin-graph. This feature may become necessary for you if your master polls many nodes and the munin-cron risks taking more than 5 minutes.

Install perl-cgi-fast.

You must enable one of these:

mod_cgid (or mod_cgi if using mpm_prefork_module) by uncommenting the line in httpd.conf.
Or install mod_fcgid and add LoadModule mod_fcgid modules/mod_fcgid.so in httpd.conf.

<VirtualHost *:80>
   ServerName localhost
   ServerAdmin  root@localhost

   DocumentRoot /srv/http/munin

   ErrorLog /var/log/httpd/munin-error.log
   CustomLog /var/log/httpd/munin-access.log combined


   # Rewrites
   RewriteEngine On

   # Static content in /static
   RewriteRule ^/favicon.ico /etc/munin/static/favicon.ico [L] 
   RewriteRule ^/static/(.*) /etc/munin/static/$1          [L] 

   # HTML
   RewriteCond %{REQUEST_URI} .html$ [or]
   RewriteCond %{REQUEST_URI} =/
   RewriteRule ^/(.*)          /usr/share/munin/cgi/munin-cgi-html/$1 [L] 

   # Images
   RewriteRule ^/munin-cgi(.*) /usr/share/munin/cgi/$1 [L] 

   <Directory "/etc/munin/static">
       Require all granted
   </Directory>

   # Ensure we can run (fast)cgi scripts
   <Directory "/usr/share/munin/cgi">
       Require all granted
       Options +ExecCGI
       <IfModule mod_fcgid.c>
           SetHandler fcgid-script
       </IfModule>
       <IfModule !mod_fcgid.c>
           SetHandler cgi-script
       </IfModule>
   </Directory>
</VirtualHost>

Nginx

Munin 2.0.x

This example Nginx setup is based on a Munin 2.0.x munin master installation. It requires FastCGI and uses the html_strategy cgi and graph_strategy cgi in the munin.conf configuration.

Install the nginx, perl-cgi-fast and perl-html-template-expr packages on the Munin-Master.

As we will be using the cgi strategy the systemd socket files need to be enabled. So the /run/munin/fcgi-graph.sock and /run/munin/fcgi-html.sock sockets are created for the Nginx FastCGI configuration to hook into.

# systemctl enable --now munin-graph.socket
# systemctl enable --now munin-html.socket

Create the munin vhost configuration file

/etc/nginx/sites-available/munin

server {
    server_name yourhost.example.com;
    listen 80;
    access_log /var/log/nginx/munin-access.log;
    error_log /var/log/nginx/munin-error.log info;
    location ^~ /munin-cgi/munin-cgi-graph/ {
        fastcgi_split_path_info ^(/munin-cgi/munin-cgi-graph)(.*);
        fastcgi_param PATH_INFO $fastcgi_path_info;
        fastcgi_pass unix:/run/munin/fcgi-graph.sock;
        include fastcgi_params;
    }
    location /munin/static/ {
        alias /etc/munin/static/;
    }
    location /munin/ {
        fastcgi_split_path_info ^(/munin)(.*);
        fastcgi_param PATH_INFO $fastcgi_path_info;
        fastcgi_pass unix:/run/munin/fcgi-html.sock;
        include fastcgi_params;
    }
}

Then restart the webserver

# systemctl restart nginx

If all goes well, point your browser to your host http://yourhost.example.com/munin/ and you should see the Munin Overview page.

Munin 2.1.x

Although Munin 2.1.x versions are not yet available in the Arch repository. It is worth mentioning that the 2.1.x series will no longer use FastCGI and will be replaced with munin-httpd This page already contains an example configuration.

Tips and Tricks

MySQL

The MySQL plugin has extra dependencies available in the AUR: perl-dbi, perl-dbd-mysql, perl-cache-cache^AUR, and perl-ipc-sharelite^AUR

Additionally it is recommended to access the database through a separate MySQL user. To make another user via the following MySQL commands:

MariaDB> CREATE USER 'muninuser'@'localhost' IDENTIFIED BY 'muninpassword';
MariaDB> GRANT SUPER,PROCESS ON *.* TO 'muninuser'@'localhost';
MariaDB> GRANT SELECT ON mysql.* TO 'muninuser'@'localhost';
MariaDB> FLUSH PRIVILEGES;

To configure Munin to use this new user, create:

/etc/munin/plugin-conf.d/mysql_

[mysql_*]
     env.mysqlconnection DBI:mysql:mysql;host=127.0.0.1;port=3306
     env.mysqluser muninuser
     env.mysqlpassword muninpassword

S.M.A.R.T.

To enable monitoring of S.M.A.R.T. data, install the smartmontools package, and use:

/etc/munin/plugin-conf.d/munin-node

[smart_*]
    user root
    group disk

Then create the appropriate symlink for each disk to be monitored. As an example for sda:

# ln -s /usr/lib/munin/plugins/smart_ /etc/munin/plugins/smart_sda

lm_sensors

Install lm_sensors and configure according to lm_sensors#Setup. Assuming all goes correctly, create some symlinks:

# ln -s /usr/lib/munin/plugins/sensors_ /etc/munin/plugins/sensors_fan 
# ln -s /usr/lib/munin/plugins/sensors_ /etc/munin/plugins/sensors_temp
# ln -s /usr/lib/munin/plugins/sensors_ /etc/munin/plugins/sensors_volt