MariaDB is a drop in place replacement for MySQL, but you can also install it alongside MySQL. (This can be useful, for example, if you want to migrate databases/applications one by one.)

Here are the steps to install MariaDB near an existing MySQL installation.

• Download the compiled binary tar.gz that contains the latest version (mariadb-5.5.24-linux-x86_64.tar.gz - as of writing this article) and extract the files in a directory of your choice. I will assume for this article that the directory was /opt.

[root@mariadb-near-mysql ~]# cat /etc/issue
CentOS release 6.2 (Final)

[root@mariadb-near-mysql ~]# rpm -qa mysql*
mysql-5.1.61-1.el6_2.1.x86_64
mysql-libs-5.1.61-1.el6_2.1.x86_64
mysql-server-5.1.61-1.el6_2.1.x86_64

[root@mariadb-near-mysql ~]# ps axf | grep mysqld
 2072 pts/0    S+     0:00          \_ grep mysqld
 1867 ?        S      0:01 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock ...
 1974 ?        Sl     0:06  \_ /usr/libexec/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql ...

• Create data directory and symlinks as below:

[root@mariadb-near-mysql opt]# mkdir mariadb-data
[root@mariadb-near-mysql opt]# ln -s mariadb-5.5.24-linux-x86_64 mariadb
[root@mariadb-near-mysql opt]# ls -al
total 20
drwxr-xr-x.  5 root root 4096 2012-06-06 07:27 .
dr-xr-xr-x. 23 root root 4096 2012-06-06 06:38 ..
lrwxrwxrwx.  1 root root   27 2012-06-06 07:27 mariadb -> mariadb-5.5.24-linux-x86_64
drwxr-xr-x. 13 root root 4096 2012-06-06 07:07 mariadb-5.5.24-linux-x86_64
drwxr-xr-x.  2 root root 4096 2012-06-06 07:26 mariadb-data

• Create group mariadb and user mariadb and set correct ownerships:

[root@mariadb-near-mysql opt]# groupadd --system mariadb
[root@mariadb-near-mysql opt]# useradd -c "MariaDB Server" -d /opt/mariadb -g mariadb --system mariadb
[root@mariadb-near-mysql opt]# chown -R mariadb:mariadb mariadb-5.5.24-linux-x86_64/
[root@mariadb-near-mysql opt]# chown -R mariadb:mariadb mariadb-data/

• Create a new my.cnf in /opt/mariadb from support files:

[root@mariadb-near-mysql opt]# cp mariadb/support-files/my-medium.cnf mariadb-data/my.cnf
[root@mariadb-near-mysql opt]# chown mariadb:mariadb mariadb-data/my.cnf

• Edit the file /opt/mariadb-data/my.cnf and add custom paths, socket, port, user and the most important of all: data directory and base directory. Finally the file should have at least the following:

[client]
port		= 3307
socket		= /opt/mariadb-data/mariadb.sock

[mysqld]
datadir         = /opt/mariadb-data
basedir         = /opt/mariadb
port		= 3307
socket		= /opt/mariadb-data/mariadb.sock
user            = mariadb

• Copy the init.d script from support files in the right location:

[root@mariadb-near-mysql opt]# cp mariadb/support-files/mysql.server /etc/init.d/mariadb
[root@mariadb-near-mysql opt]# chmod +x /etc/init.d/mariadb

• Edit /etc/init.d/mariadb replacing mysql with mariadb as below:

- # Provides: mysql
+ # Provides: mariadb
- basedir=
+ basedir=/opt/mariadb
- datadir=
+ datadir=/opt/mariadb-data
- lock_file_path="$lockdir/mysql"
+ lock_file_path="$lockdir/mariadb"

The trickiest part will be the last changes to this file. You need to tell mariadb to use only one cnf file. In the start section after $bindir/mysqld_safe add --defaults-file=/opt/mariadb-data/my.cnf. Finally the lines should look like:

# Give extra arguments to mysqld with the my.cnf file. This script
# may be overwritten at next upgrade.
$bindir/mysqld_safe --defaults-file=/opt/mariadb-data/my.cnf --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null 2>&1 &

The same change needs to be made to the mysqladmin command below in the wait_for_ready() function so that the mariadb start command can properly listen for the server start. In the wait_for_ready() function, after $bindir/mysqladmin add --defaults-file=/opt/mariadb-data/my.cnf. The lines should look like:

wait_for_ready () {
[...]
    if $bindir/mysqladmin --defaults-file=/opt/mariadb-data/my.cnf ping >/dev/null 2>&1; then

• Run mysql_install_db by explicitly giving it the my.cnf file as argument:

[root@mariadb-near-mysql opt]# cd mariadb
[root@mariadb-near-mysql mariadb]# scripts/mysql_install_db --defaults-file=/opt/mariadb-data/my.cnf

• Now you can start MariaDB by

[root@mariadb-near-mysql opt]# /etc/init.d/mariadb start
Starting MySQL...                                          [  OK  ]

• Make MariaDB start at system start:

[root@mariadb-near-mysql opt]# cd /etc/init.d
[root@mariadb-near-mysql init.d]# chkconfig --add mariadb 
[root@mariadb-near-mysql init.d]# chkconfig --levels 3 mariadb on

• Finally test that you have both instances running:

[root@mariadb-near-mysql ~]# mysql -e "SELECT VERSION();"
+-----------+
| VERSION() |
+-----------+
| 5.1.61    |
+-----------+
[root@mariadb-near-mysql ~]# mysql -e "SELECT VERSION();" --socket=/opt/mariadb-data/mariadb.sock
+----------------+
| VERSION()      |
+----------------+
| 5.5.24-MariaDB |
+----------------+

What about MariaDB Upgrades ?

By having the mariadb.socket, my.cnf file and databases in /opt/mariadb-data if you want to upgrade the MariaDB version you will will only need to:

• extract the new version from the archive in /opt near the current version
• stop MariaDB
• change the symlink mariadb to point to the new directory
• start MariaDB
• run upgrade script... but remember you will need to provide the socket option --socket=/opt/mariadb-data/mariadb.sock