# Munin

From the project web page:

  Munin the monitoring tool surveys all your computers and remembers what it saw. It presents all the information in graphs through a web interface. Its emphasis is on plug and play capabilities. After completing a installation a high number of monitoring plugins will be playing with no more effort.

  Using Munin you can easily monitor the performance of your computers, networks, SANs, applications, weather measurements and whatever comes to mind. It makes it easy to determine "what's different today" when a performance problem crops up. It makes it easy to see how you're doing capacity-wise on any resources.

  Munin uses the excellent RRDTool (written by Tobi Oetiker) and the framework is written in Perl, while plugins may be written in any language. Munin has a master/node architecture in which the master connects to all the nodes at regular intervals and asks them for data. It then stores the data in RRD files, and (if needed) updates the graphs. One of the main goals has been ease of creating new plugins (graphs). [1]

Simply put, Munin allows you to make graphs about system statistics. You can check out University of Oslo's Munin install to see some examples of what it can do.

## Installation

Munin relies on a client-server model. The client is munin-node, and the server is munin (referred as to "munin-master" in the documentation).

You will only need to install munin on a single machine, but munin-node will need to be installed on all machines you wish to monitor. The munin-node can also be installed together with munin on the master so the the master machine can monitor itself. Further documentation may be found on the Munin documentation wiki.

### munin and munin-node

Install the munin (munin master) and munin-node packages.

## 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

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 doesn't 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:

- perl-socket6
- perl-io-socket-inet6

#### 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.servce`. 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 HowToWritePlugins 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:

- Apache
- Lighttpd
- Nginx

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

### Apache

#### Apache VirtualHost examples

Based on information found here:

- http://guide.munin-monitoring.org/en/stable-2.0/example/webserver/apache-virtualhost.html
- http://munin-monitoring.org/wiki/MuninConfigurationMasterCGI

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

- 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 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

        # 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>

#### 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-cache-cacheAUR, and perl-ipc-shareliteAUR

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

Category:

- Status monitoring and notification