准备工作：
[root@yaojiansong /]#yum install -y wget vim ntpd
CentOSx.x下yum安装MySQL5.5/5.6
1. 安装mysql-5.5的yum源
[root@yaojiansong yum.repos.d]#rpm -ivh http://repo.mysql.com/yum/mysql-5.5-community/el/6/x86_64/mysql-community-release-el6-5.noarch.rpm
安装MySQL5.6的可以安装：
[root@yaojiansong yum.repos.d]# # rpm -ivh http://repo.mysql.com/mysql-community-release-el6.rpm
最新的yum源可以去 http://dev.mysql.com/downloads/repo/yum下载
2. 修改安装好的yum源
[root@yaojiansong yum.repos.d]#vim /etc/yum.repos.d/mysql-community.repo文件，
将5.5的enabled改为1；5.6的enabled改为0(1：启用，0：警用)
[root@yaojiansong yum.repos.d]# vim mysql-community.repo
Enable to use MySQL 5.5
[mysql55-community]
name=MySQL 5.5 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.5-community/el/6/$basearch/
enabled=1
gpgcheck=1
gpgkey=file:/etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
Enable to use MySQL 5.6
[mysql56-community]
name=MySQL 5.6 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.6-community/el/6/$basearch/
enabled=0
gpgcheck=1
gpgkey=file:/etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
1[root@yaojiansong yum.repos.d]# yum -y install mysql-community-client mysql-community-devel mysql-community-server php-mysql
2.安装mysql-5.5(只需等待，无需操作)
3. 调整配置
[root@yaojiansong yum.repos.d]# vim /etc/my.cnf
在[mysqld]下添加
innodb_file_per_table=1 设置InnoDB为独立表空间模式，每个数据库的每个表都会生成一个数据目录
innodb_buffer_pool_size= 默认值：128M，设置为操作系统内存的70%-80%最佳
4. 启动mysql，查看mysql版本
[root@yaojiansong yum.repos.d]# service mysqld start
Starting mysqld: [ OK ]
[root@yaojiansong yum.repos.d]# mysql --version （当前版本）
mysql Ver 14.14 Distrib 5.5.58, for Linux (x86_64) using readline 5.1