Install Mysql5.5 on Centos6 through repo https://www.mellzamora.com/installing-mysql-5-5-on-centos-6-via-remi-repository/#comment-278

gistfile1.txt

Add REMI repository:
## Remi Dependency on CentOS 6 and Red Hat (RHEL) 6 ##
rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
 
## CentOS 6 and Red Hat (RHEL) 6 ##
rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-6.rpm

## check available mysql version ##
yum --enablerepo=remi,remi-test list mysql mysql-server

Install MySQL:
# yum --enablerepo=remi,remi-test install mysql mysql-server

## Add to /etc/sysconfig/iptables ##

Iptables:
-A INPUT -m state --state NEW -m tcp -p tcp --dport 3306 -j ACCEPT

## Restart iptables ##
service iptables restart