转自https://www.cnblogs.com/wsl222000/p/5445768.html
1.安装mysql-5.5的yum源
rpm -ivh http://repo.mysql.com/yum/mysql-5.5-community/el/6/x86_64/mysql-community-release-el6-5.noarch.rpm
要安装MySQL5.6的可以安装：
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
编辑 /etc/yum.repos.d/mysql-community.repo文件，将5.5的enabled改为1,5.6的enabled改为0
# 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
3.安装mysql-5.5
yum install mysql-community-client mysql-community-devel mysql-community-server php-mysql
4.调整配置
编辑 /etc/my.cnf 文件
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
service mysqld start 启动mysql
chkconfig mysqld on 设为开机启动
mysqladmin -u root password ‘root‘ 设置密码为root
