First of all, MariaDB is a fork of MySQL. So, if you're using a version from 5.1 to 5.5, the migration will be really easy. To make it clear and simple, if you're running a MySQL version under 5.1, upgrade it first to 5.1 at least and 5.5 at max.

Then, it will be easy to migrate. First of all, you need to understand the best compatibility version, as shown in the following table:

It is recommended, for example, to switch from the 5.1 version of MySQL to the 5.1 version of MariaDB. Then test it, see if everything is fine, and then you can upgrade to a higher version of MariaDB.

There is something that you should consider: starting from the 5.6 version of MySQL, MariaDB will start to number the version from 10. Why? Because MariaDB developers want to be clear on the features portability from MySQL to MariaDB. All the features won't be ported in version 10. They may be done later or not at all. Some features will be fully rewritten for several reasons, and MariaDB developers will try to keep compatibility with MySQL. That's why for a migration, it's preferable to migrate a MySQL version from 5.1 to 5.5. If you don't use advanced features, it shouldn't be a problem as incompatibilities are very low.

Since 5.5 is really stable, you can skip the upgrade to 5.3 (the latest branch of MariaDB based on 5.1) and go straight to 5.5. Of course, complete regression testing of the application is recommended.

To get more information on the compatibility list from one version to another, I strongly recommend following the official MariaDB compatibility information page available on the main site: https://mariadb.com/kb/en/mariadb-versus-mysql-compatibility/.

Now that you've understood how to migrate, we'll perform a migration using a virtual machine. You'll need the following:

This is the code you need to run:

# -*- mode: ruby -*-
# vi: set ft=ruby :
ENV['LANG'] = 'C'

# Vagrantfile API/syntax version. Don't touch unless you know what you're doing!
VAGRANTFILE_API_VERSION = "2"

# Insert all your Vms with configs
boxes = [
    { :name => :mysqlserver },
]

$install = <<INSTALL
aptitude update
DEBIAN_FRONTEND=noninteractive aptitude -y -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" install mysql-server
INSTALL

Vagrant::Config.run do |config|
  # Default box OS
  vm_default = proc do |boxcnf|
    boxcnf.vm.box       = "deimosfr/debian-wheezy"
  end

  # For each VM, add a public and private card. Then install Ceph
  boxes.each do |opts|
    vm_default.call(config)
    config.vm.define opts[:name] do |config|
        config.vm.host_name = "%s.vm" % opts[:name].to_s
        config.vm.provision "shell", inline: $install
    end
  end
end

Install on this virtual machine the application of your choice (WordPress, MediaWiki, and so on) to confirm the migration doesn't break anything.

You will see that the migration is an easy step. First of all, remove the current MySQL version, but keep the data:

apt-get remove mysql-server

Then, your database will still be available in the data directory (/var/lib/mysql by default) but no binary will be present.

It's time to install MariaDB. First add the MariaDB repository (for version 5.5 here):

apt-get install python-software-properties
apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 0xcbcb082a1bb943db
add-apt-repository 'deb http://mirrors.linsrv.net/mariadb/repo/5.5/debian wheezy main'

Now install MariaDB:

apt-get update
apt-get install mariadb-server

It should have started without any issues. Take a look at the logs in /var/log/syslog if this is not the case.