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Munin is popular monitoring software that logs all types of server performance and presents and graphed information. It can be a very handy tool for diagnosing "what just happened" situations. The end result of this guide will be to install a basic Munin configuration that has graphical representations of more core performance metrics.

1. The first thing we'll do is perform the install. Because the default repository does not include what we need, that needs updated before yum knows what to do:

   rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm
   

   yum -y install munin munin-node
   

2. Now, we just have to set about configuring what has been installed. First off, we'll make a backup of the original config file (in case you'd like to refer to it later) and create one specific to how this will be set up:

   mv /etc/munin/munin.conf /etc/munin/munin.conf-original
   

   cat <<EOF > /etc/munin/munin.conf
   dbdir   /var/lib/munin
   htmldir /var/www/munin
   logdir  /var/log/munin
   rundir  /var/run/munin
   tmpldir /etc/munin/templates
   [localhost]
   address 127.0.0.1
   use_node_name yes
   EOF
   

3. Munin comes armed with an incredible number of plug-ins. And it has a user base that add more for custom use every day. The yum installation we used automatically enables monitoring of a number of core system processes; however, there are a few others turned off by default that are specifically for Apache and MySQL, which means they are useful for the (dv) Dedicated-Virtual server environment. This command turns them on by linking into the plugins directory:

   for i in apache_accesses apache_processes apache_volume mysql_ mysql_innodb mysql_isam_space_ mysql_queries mysql_slowqueries mysql_threads; do ln -s /usr/share/munin/plugins/$i /etc/munin/plugins/; done
   

4. In order to make use of all the graphs Munin puts together, there needs to be a directory the data lives in:

   mkdir -p /var/www/munin
   

   chown -R munin:munin /var/www/munin
   

5. In order to make this data web accessible, we add a new apache configuration that aliases to it:

   cat <<EOF > /etc/httpd/conf.d/munin.conf
   Alias /.munin /var/www/munin
   <Directory /var/www/munin>
   AuthType Basic
   AuthName "Munin Login"
   AuthUserFile /var/www/munin/.htpasswd
   require valid-user
   </Directory>
   EOF
   

In order for Munin to gather status for the Apache (httpd) process, you'll need to enable 'ExtendedStatus' by editing the Apache configuration (/etc/httpd/conf/httpd.conf) file. To allow ExtendedStatus,... enable mod_status.so module if not already enabled uncomment the following lines:
* Located on line 176 by default

LoadModule status_module modules/mod_status.so

then uncomment the following lines:
* Located on line 217 by default

ExtendedStatus On

* Located on lines 903-908 by default

<Location /server-status>
SetHandler server-status
Order deny,allow
Deny from all
Allow from 127.0.0.1
</Location>

In order for Munin to gather status for the MySQL (mysqld) process, you'll need to create a MySQL monitor user.

mysql> CREATE USER 'mysqlmonitor'@'localhost' IDENTIFIED BY '3n9kdS2RzzSB';
mysql> GRANT PROCESS ON *.* TO 'mysqlmonitor'@'localhost';
mysql> FLUSH PRIVILEGES;

Then you will need to edit /etc/munin/plugin-conf.d/munin-node and add the following:

[mysql*]
env.mysqlopts -umysqlmonitor -p3n9kdS2RzzSB

6. And now, login credentials need set. The command below will cause Munin to use Plesk's admin credentials. If you would prefer to use a different username and/or password, simply replace the latter two flags for this command, which are username and password respectively:

   htpasswd -bc /var/www/munin/.htpasswd admin $(cat /etc/psa/.psa.shadow)
   

7. We want Munin's password to stay up to date in case Plesk is ever updated. If you did not want to use Plesk's credentials in the previous command, skip this step.

   cat <<EOF > /usr/local/psa/admin/sbin/munin_password_change.sh
   #!/bin/bash
   passCheck="$(md5sum /etc/psa/.psa.shadow | awk '{print $1}')"
   if [[ ! "\$passCheck" = \$(md5sum /etc/psa/.psa.shadow | awk '{print \$1}') ]]; then
   htpasswd -b /var/www/munin/.htpasswd admin $(cat /etc/psa/.psa.shadow)
   perl -p -i -e 's/^(passCheck\=\")[^\n]+/passCheck\=\"'\$(md5sum /etc/psa/.psa.shadow | awk '{print \$1}')'\"/' /usr/local/psa/admin/sbin/munin_password_change.sh
   /etc/init.d/munin-node restart
   fi
   EOF
   

   echo "* * * * * /usr/local/psa/admin/sbin/munin_password_change.sh" >> /var/spool/cron/root
   

   Unfortunately, Plesk does not currently provide an event handler for the admin password changing, so updating other software with these credentials requires a cron of this nature.
8. Make sure that Munin starts on its own on server reboots:

   chkconfig --levels 235 munin-node on
   

9. At this point everything is ready to start. Since both Munin and Apache configurations were updated, both need to restart with the new directives:

   /etc/init.d/munin-node restart
   

   /etc/init.d/httpd restart
   

cat <<EOF > /etc/monit.d/munin.mon
check process munin-node with pidfile /var/run/munin/munin-node.pid
start program "/etc/init.d/munin-node start"
stop program "/etc/init.d/munin-node stop"
if cpu > 90% for 5 cycles then restart
if 5 restarts within 5 cycles then timeout
EOF

You can now view your Munin graphs by browsing to http://your_ip_here/.munin or http://your_domain_here/.munin and logging in with your Plesk admin credentials (*unless you manually chose to use a different username/password). It will take Munin about 5 minutes to start logging data. The homepage will show every graph with the past day and week. Each graph will display a description of what it is displaying by clicking on it, as well as the past month and year.