、安装MySQL 5.5.x的yum源：
rpm -Uvh http://repo.webtatic.com/yum/centos/5/latest.rpm
2、安装MySQL客户端的支持包：yum install libmysqlclient15 --enablerepo=webtatic
3、卸载MySQL老版本的软件包：yum remove mysql mysql-*
4、安装MySQL 5.5的客户端和服务端：yum install mysql55 mysql55-server --enablerepo=webtatic
5、启动MySQL系统服务，更新数据库：
/etc/init.d/mysqld restart
mysql_upgrade
6、附：此台服务器的my.cnf配置
skip-locking
skip-name-resolve
key_buffer = 1024M
back_log = 3000
max_allowed_packet = 4M
table_cache = 512
sort_buffer_size = 8M
read_buffer_size = 8M
myisam_sort_buffer_size = 1024M
thread_cache = 512
query_cache_size = 512M
set-variable = wait_timeout=60
thread_concurrency = 4
log-slow-queries = slow.log
long_query_time = 1
innodb_flush_log_at_trx_commit = 2
innodb_buffer_pool_size = 1024M
#innodb_locks_unsafe_for_binlog = 1