一、mysql_install_db说明
当MySQL的系统库（mysql系统库）发生故障或需要新加一个mysql实例时，需要初始化mysql数据库。

需要使用的命令：/usr/local/mysql/bin/mysql_install_db
 #/usr/local/mysql/bin/mysql_install_db --help 可以查看帮助信息如下
 Usage: /usr/local/mysql/bin/mysql_install_db [OPTIONS]
 –basedir=path The path to the MySQL installation directory.
 –cross-bootstrap For internal use. Used when building the MySQL system
 tables on a different host than the target.
 –datadir=path The path to the MySQL data directory.
 –force Causes mysql_install_db to run even if DNS does not
 work. In that case, grant table entries that normally
 use hostnames will use IP addresses.
 –ldata=path The path to the MySQL data directory.
 –rpm For internal use. This option is used by RPM files
 during the MySQL installation process.
 –skip-name-resolve Use IP addresses rather than hostnames when creating
 grant table entries. This option can be useful if
 your DNS does not work.
 –srcdir=path For internal use. The directory under which
 mysql_install_db looks for support files such as the
 error message file and the file for popoulating the
 help tables.
 –user=user_name The login username to use for running mysqld. Files
 and directories created by mysqld will be owned by this
 user. You must be root to use this option. By default
 mysqld runs using your current login name and files and
 directories that it creates will be owned by you.All other options are passed to the mysqld program
 除了支持以上的参数，还支持mysqld的参数。

二、举例：
本文以新加一个mysql实例为例。例如服务器上已经安装了3306端口的mysql服务，需要再启一个3308端口的mysql服务。
假设mysql安装在/usr/local/mysql路径下，找一个磁盘空间剩余比较大的盘，如/data1，把3308端口的mysql的数据保存在/

data1下
 #mkdir /data1/mysql_3308
 #mkdir /data1/mysql_3308/data
 #chown -R mysql:mysql /data1/mysql_3308复制一个mysql配置文件my.cnf到/data1/mysql_3308目录下
 #vi /data1/mysql_3308/my.cnf
 修改配置文件，将端口和相关目录的都改为新的设置，如下：
 [client]
 character-set-server = utf8
 port = 3308
 socket = /tmp/mysql_3308.sock[mysqld]
 user = mysql
 port = 3308
 socket = /tmp/mysql_3308.sock
 basedir = /usr/local/mysql
 datadir = /data1/mysql_3308/data
 log-error = /data1/mysql_3308/mysql_error.log
 pid-file = /data1/mysql_3308/mysql.pid
 …其他略

确保配置文件无误。
运行下面命令进行数据库的初始化：
#/usr/local/mysql/bin/mysql_install_db --defaults-file=/data1/mysql_3308/my.cnf --datadir=/data1/mysql_3308/data

完成后新的3308数据库就初始化好了，如果有报错，则按照报错的提示查看报错日志，一般情况下都是my.cnf配置文件的问题，修正后即可。

三、启动新mysql

启动3308端口的mysql服务
 #/usr/local/mysql/bin/mysqld_safe --defaults-file=/data1/mysql_3309/my.cnf &
 检查是否启动
 #ps aux|grep mysql
 如果有3308字样说明已经启动成功
 可将启动命令加入/etc/rc.local随服务器启动新加的mysql没有设置root密码，可以通过下面命令设置root密码：
 #/usr/local/mysql/bin/mysqladmin -S /tmp/mysql_3308.sock -u root password ‘new-password’