How To Setup Munin on Ubuntu 12.04 LTS

Assumption: You will access munin using the server IP adress
(there are several ways to setup and access munin, but in a VirtualHost environment it may not be desirable to setup/access via a VirtualHost.)

sudo apt-get install munin munin-node

sudo vi /etc/munin/apache.conf

Allow from localhost ::1

# Replace with this
Allow from all

# add this line just above the following lines
AllowOverride None

# uncomment these lines
AuthUserFile /etc/munin/munin-htpasswd
AuthName “Munin”
AuthType Basic
require valid-user

Set the login user Munin password

sudo htpasswd -c /etc/munin/munin-htpasswd Munin

Change the permissions (very important or you will get a 500 error – and no other How To for Ubuntu points this out)

sudo chmod 644 /etc/munin/munin-htpasswd

Change the Node IP to the server IP address

sudo vi /etc/munin/munin-node.conf

allow ^127\.0\.0\.1$

# Replace this with the server IP address
allow ^123\.123\.123\.123$

sudo service apache2 restart
sudo service munin-node restart

You should be good to go!
In your browser got to
User is Munin