Munin configuration and testing on Ubuntu

This article continues the installation and setup of munin on a single slice. It explains how to determine or change the URL used to access munin's reports and then check to make sure those reports are viewable and being updated.


Almost ready!

If you've been following along with the first article in this series, Installing munin, you should now have a munin master configured on your slice and have a node running and gathering data every five minutes. All that's left now is to see if you can access the reports munin generates. To do that you'll need to make sure munin is storing its generated html files in a location you can access through your web server.

The htmldir setting

If you go back to the configuration file at /etc/munin/munin.conf, toward the beginning you will find an entry that looks like:

# The next three variables specifies where the location of the RRD
# databases, the HTML output, and the logs, severally.  They all
# must be writable by the user running munin-cron.
dbdir   /var/lib/munin
htmldir /var/www/munin
logdir  /var/log/munin
rundir  /var/run/munin

The line you want to look at is the "htmldir" value. This is the directory where munin stores its web pages, and the default value is a subdirectory of the web server's default document root (more on that later). If you would prefer that munin store its pages in another location (as a subdirectory of an existing site, for instance) you can change that line to a new directory. Just make sure that you set the new directory to be writeable by the munin user or munin won't be able to generate graphs and reports there.

If you aren't sure if the munin HTML directory can be written to by the munin user, the easiest fix is to set the ownership of the directory (which is done for you in a default install). To set the ownership of the directory to the munin user, run the following command:

chown -R munin /var/www/munin

If you aren't using the default munin directory, make sure to substitute the new directory for "/var/www/munin" in the example above.

Determining the munin URL

The URL used to access munin's reports is a combination of the address you use to access your web server and where the munin HTML directory is relative to the web server's document root. Let's take a look at how you can check these details in a default apache install so you can find and change these settings when you need to.

A closer look at the default site

When apache is installed it sets up two directories to manage the sites that apache will serve to visitors. One directory, /etc/apache2/sites-available, contains a file for each site. By default it contains just one file, appropriately named "default". The other directory is /etc/apache2/sites-enabled, which contains links to the configuration files for sites apache should actually allow people to visit. If you haven't changed apache's configuration there will be a symlink from sites-enabled to the default file in sites-available, letting apache know to serve that site.

If you want to enable or disable another virtual host, revisit the article you used to set up apache for more details.

For now we're interested in how the site is set up, so we'll look at the default site to find those details. Open the file:

/etc/apache2/sites-available/default

Let's look at the first part of that file, which by default would be:

NameVirtualHost *
<VirtualHost *>
    ServerAdmin webmaster@localhost

    DocumentRoot /var/www/
    <Directory />
        Options FollowSymLinks
        AllowOverride None
    </Directory>
    <Directory /var/www/>
        Options Indexes FollowSymLinks MultiViews
        AllowOverride None
        Order allow,deny
        allow from all
    </Directory>
...

The first lines, "NameVirtualHost *" and "", basically tell apache that this default site configuration will handle every request that comes into the web server. If you've already set up another site configuration those lines will look different, since they're generally changed when someone wants a more specific site set-up (for a specific domain or for multiple domains). For the purposes of setting up munin, you mostly just need to know that if those lines change in the future you may need to make allowances to continue to access munin's html directory.

The next directive we want to check is a couple lines further down, "DocumentRoot /var/www/". That option tells apache where the web files are stored for this virtual host. That default setting means that if you visit this virtual host apache will look in /var/www to find any pages to show the user. If you have "www.example.com" pointing to your slice, for example, you could see the default index file in the virtual host's document root by going to this URL:

http://www.example.com

If munin's web directory is not located in the site's document root, either because you've changed apache's configuration or because you don't want the munin files to be in the document root, you have a couple options. One option is to change the munin.conf file to use a directory in a different document root (using the instructions above under the heading, "The htmldir in munin.conf"). There is another option that doesn't involve changing where munin stores its reports, however, and that is...

The Alias directive

The Alias directive in apache lets you set up an alias from a reference to a subdirectory of the document root to a location somewhere else in your slice's filesystem. For example, if your document root were "/var/www" but you wanted your munin HTML files to be in "/home/munin/public_html", you would set up an alias from "/munin" to "/home/munin/public_html".

The Alias directive depends on the module "mod_alias" being enabled. This mod is included and enabled in the default apache installation.

To add an alias like the example above you would want to add the alias to your site configuration in /etc/apache2/sites-available, and would need to include a Directory entry for the directory the alias points to. The new section can be inserted near the end of the file, so long as it comes before the " entry. Your configuration might look like:

Alias /munin /home/munin/public_html
<Directory /home/munin/public_html>
    Options FollowSymLinks
    AllowOverride None
    Order allow,deny
    Allow from all
</Directory>

Once the Alias and Directory configuration is added to your site, you'll need to restart apache for the change to take effect.

Wasn't there something about a URL?

Now that you know where munin (or an Alias to it) is in relation to your web server's document root, finding the address of the munin reports is a matter of putting together the URL of your site and the location of munin's web pages within that site.

When you go to your base URL, like, "http://www.example.com", you're telling the web server you want to see the content in your site's document root, let's say "/var/www". When you go to your site with that address there's actually an implied slash at the end of the URL. Let's add that slash to make it easier to see the relationship between the URL and the document root:

http://www.example.com/

You can think of that last slash in your base URL as meaning "look in my document root". Since we're assuming /var/www for this example, that means "/" means "/var/www/". Now look at where the munin web directory is located in our example, "/var/www/munin". If you substitute a slash for the /var/www/ part, you get simply "/munin". Now we can put the base URL together with the relative munin location that you just worked out, and get:

http://www.example.com/munin

And there you have the address you visit in a browser to look at munin's reports. Most importantly, you have an idea of how we came up with it. You can change settings on your web server or in munin later and know how those changes could affect the address you use to see munin's web pages.

See the results

Munin collects data and generates new graphs every five minutes. If it hasn't been five minutes since you configured munin you may need to wait a little bit before there are web pages generated in the munin HTML directory. Also expect your initial graphs to be pretty sparse since there won't be much data for munin to use when drawing lines.

Point your web browser to the URL you determined above and let's see what comes up. Hopefully you'll see the host name you put into the munin.conf file, similar to:

Munin overview page

If you get a "not found" error you may need to review this article to see if you missed a settings change or need to make the munin web directory writeable by the munin user. You might also check the web server logs in /var/log/apache2 and the munin logs in /var/log/munin for clues.

Clicking the first name in the list on the munin overview page (in the screenshot, the first "jered") will show a list of graph categories:

Munin node page

Once you've confirmed that the pages are being created and can be reached, wait a half hour or so to let munin accumulate enough data to draw the beginnings of a few graphs. If you click the second hostname entry on the overview page you'll get a page with all generated graphs on it. The following shots are from a munin instance that's been running a few days, to make the graphs easier to spot:

Munin graphs page

Pretty boring stuff at the top on the example server, since it's been mostly idle. You can see more active graphs if you scroll down to the system section:

Munin system graphs

From here it's just a matter of checking in on munin's reports every now and then to watch the trends and to follow up on any emails munin sends you. Keep an eye out for things like swap in/out (ideally there should be almost none), regularly high non-idle cpu use, and spikes in bandwidth use ("eth0 traffic").

For more information on the data munin reports check the documentation and FAQ at the munin project's web site.

Summary

In this article we looked at configuring the munin HTML directory and the web server's document root, and how to put that information together to get the web address for viewing the munin reports. We also viewed the munin reports to make sure they were accessible and updating.

Future articles in this series will cover installing nodes on additional slices (so you can monitor multiple slices from one munin master) and customizing munin by adding more plug-ins or improving security on the data it's generating.

If you're content with the default plug-ins and a single node, you need go no further. You're all set!

  • -- Jered

Article Comments:

David C commented Fri Mar 12 22:53:09 UTC 2010:

Is there any easy way to set up simple password authentication to prevent the internet from seeing these stats munin is putting out using the domain name I set up?

Jered commented Sat Mar 13 20:00:02 UTC 2010:

There is, and an article on the subject is planned. In a nutshell you can use apache's htpasswd command to set up a user and password pair, and then configure apache to protect a directory with it. Nginx has a similar feature. For now, there's a decent tutorial on the subject here.

Z commented Wed Feb 09 07:18:09 UTC 2011:

Thanks for these instructions :), I'm wondering if you guys ever got around to an article on password protecting munin? The thing is I ended up using an Alias and so I think thats stopping my .htaccess from working properly...

Z commented Wed Feb 09 15:12:44 UTC 2011:

Nevermind, I figured out the issue :P

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