执行mysql_secure_installation报错
错误现象：
Enter current password for root (enter for none):
ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/tmp/mysql.sock’ (2)
错误原因：
mysql_secure_installation ignores –socket
解决方案：
1）ln -s /var/run/mysqld/mysqld.sock /tmp/mysql.sock
2）修改mysql_secure_installation 脚本的do_query 函数（推荐处理方法）
do_query() {
echo “$1” >$command
#sed ‘s,^,> ,’ < $command # Debugging # mysql --defaults-file=$config <$command ----此行修改如下： mysql --defaults-extra-file=$config <$command return $? } 使用mysqld_safe启动msql错误
见mysqld_safe启动报错

注意：如果想把错误日志放到专门的日志目录中，需要在my.cnf中添加log-error=path选项
mysql二进制文件安装指导和my.cnf文件

使用二进制编译文件的mysqld_safe启动报错，如下：
[mysql@ECP-UC-DB1 ~]$ mysqld_safe
110707 21:31:19 mysqld_safe Logging to ‘/opt/mysql/mysqldata/ECP-UC-DB1.err’.
110707 21:31:19 mysqld_safe The file /usr/local/mysql/bin/mysqld
does not exist or is not executable. Please cd to the mysql installation
directory and restart this script from there as follows:
./bin/mysqld_safe&
See http://dev.mysql.com/doc/mysql/en/mysqld-safe.html for more information

解决方法：
su – root
mkdir /usr/local/mysql/bin
ln -s /opt/mysql/product/5.5/bin/mysqld /usr/local/mysql/bin/mysqld

再次执行mysqld_safe
[mysql@ECP-UC-DB1 ~]$ mysqld_safe
110707 21:32:37 mysqld_safe Logging to ‘/opt/mysql/mysqldata/ECP-UC-DB1.err’.
110707 21:32:37 mysqld_safe Starting mysqld daemon with databases from /opt/mysql/mysqldata

启动结果：
mysql 26885 23452 0 21:32 pts/0 00:00:00 /bin/sh /opt/mysql/product/5.5/bin/mysqld_safe
mysql 27653 26885 0 21:32 pts/0 00:00:00 /usr/local/mysql/bin/mysqld –basedir=/opt/mysql/product/5.5 –datadir=/opt/mysql/mysqldata –plugin-dir=/usr/local/mysql/lib/plugin –log-error=/opt/mysql/mysqldata/ECP-UC-DB1.err –open-files-limit=8192 –pid-file=/var/run/mysqld/mysqld.pid –socket=/var/run/mysqld/mysqld.sock –port=3306

问题存在原因：
1、mysqld_safe只认识/usr/local/mysql/bin/mysqld（也许是配置问题）
2、my.cnf只能放置在/etc/下面，不然使用–defaults-file也不能读取my.cnf文件（有疑惑）

1、数据库实例目录
drwxrwxrwx 6 mysql mysql 4096 Jul 6 23:25 mysqldata
drwxrwxr-x 5 mysql mysql 4096 Jul 6 23:23 mysqldata1
drwxrwxr-x 5 mysql mysql 4096 Jul 6 23:27 mysqldata2

2、创建实例
/opt/mysql/product/5.5/scripts/mysql_install_db –basedir=/opt/mysql/product/5.5 –datadir=/opt/mysql/mysqldata –user=mysql
/opt/mysql/product/5.5/scripts/mysql_install_db –basedir=/opt/mysql/product/5.5 –datadir=/opt/mysql/mysqldata1 –user=mysql
/opt/mysql/product/5.5/scripts/mysql_install_db –basedir=/opt/mysql/product/5.5 –datadir=/opt/mysql/mysqldata2 –user=mysql

3、修改my.cnf文件
[mysqld_multi]
mysqld = /opt/mysql/product/5.5/bin/mysqld
mysqladmin = /opt/mysql/product/5.5/bin/mysqladmin
user = root
password = passw0rd

[mysqld3306]
port = 3306
socket = /var/run/mysqld/mysqld3306.sock
pid-file = /var/run/mysqld/mysqld3306.pid
basedir = /opt/mysql/product/5.5
datadir = /opt/mysql/mysqldata

[mysqld3307]
port = 3307
socket = /var/run/mysqld/mysqld3307.sock
pid-file = /var/run/mysqld/mysqld3307.pid
basedir = /opt/mysql/product/5.5
datadir = /opt/mysql/mysqldata1

[mysqld3307]
port = 3307
socket = /var/run/mysqld/mysqld3308.sock
pid-file = /var/run/mysqld/mysqld3308.pid
basedir = /opt/mysql/product/5.5
datadir = /opt/mysql/mysqldata2
注：其他无关参数省略，日志等文件路径也不能相同（未写明）

4、启动数据库
mysqld_multi –defaults-file=/etc/mysql/my.cnf start 3306
mysqld_multi –defaults-file=/etc/mysql/my.cnf start 3307
mysqld_multi –defaults-file=/etc/mysql/my.cnf start 3308

5、登录数据库修改root密码
mysql -S /var/run/mysqld/mysqld3306.sock
mysql -S /var/run/mysqld/mysqld3307.sock
mysql -S /var/run/mysqld/mysqld3308.sock

use mysql
UPDATE user SET password=PASSWORD(‘passw0rd’) WHERE user=’root’;
FLUSH PRIVILEGES;
说明：三个库上分别操作

6、关闭数据库
mysqld_multi –defaults-file=/etc/mysql/my.cnf stop 3306
mysqld_multi –defaults-file=/etc/mysql/my.cnf stop 3307
mysqld_multi –defaults-file=/etc/mysql/my.cnf stop 3308

7、全部启动/关闭
mysqld_multi –defaults-file=/etc/mysql/my.cnf start 3306-3308
mysqld_multi –defaults-file=/etc/mysql/my.cnf stop 3306-3308