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# 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/start `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.

By runnning the `munin-cron` command manually as the `munin` user, 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, enable/start `munin-node.service`.

#### 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.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:

- Apache HTTP Server
- Lighttpd
- Nginx

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

### Apache

#### Apache VirtualHost examples

This article or section is out of date.

Reason: This section speaks of "the next major release" with a link that had to be replaced with a 2018 copy of the documentation. Surely things have changed in those years. (Discuss in Talk:Munin)

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[dead link 2021-05-17 ⓘ]

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_fcgidAUR 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_fcgidAUR 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.

Enable/start `munin-graph.socket` and `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 (`nginx.service`).

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: perl-dbi, perl-dbd-mysql, 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#Configuration. 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:

- System monitors

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