（一）MYSQL ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.10.210' (111) ...

今天在测试MySQL的链接时候，发现链接不经过，并报错ERROR 2003 (HY000): Can't connect to mysql server on '192.168.10.210' (111) 
测试代码：

require 'mysql2'
client = Mysql2::Client.new(:host=>"192.168.10.210",:username=>'root',:password=>"root")
puts results = client.query("show databases;")

谷歌了一下以后，原来是在mysql的my.cnf中有下面一段代码：

# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address           = 127.0.0.1  #这里默认监听本地localhost

若是要让mysql监听到其余的地址，能够将bind-address = 127.0.0.1注释掉。 
或者将bind-address = 0.0.0.0监听全部的地址

屏蔽掉以后再次运行代码又出现：Host '192.168.10.83' is not allowed to connect to this MySQL server 
 
解决方法： 
若是想让192.168.10.83可以链接到本地的这个数据库，要让数据库给其分配权限,登陆mysql，执行:(username 和 password是登陆mysql的用户名和密码)

GRANT ALL PRIVILEGES ON *.* TO 'username'@'192.168.10.83' IDENTIFIED BY 'password' WITH GRANT OPTION;

若是要想全部的外部ip地址都可以访问使用mysql，能够执行下面：(此处是对root用户受权mysql全部数据库)

GRANT ALL PRIVILEGES ON *.* TO 'username'@'%' IDENTIFIED BY 'password' WITH GRANT OPTION;

若是针对某个特定的用户test受权某个指定的数据testdb用下面例子中的命令

mysql>GRANT ALL PRIVILEGES ON `testdb`.* TO 'test'@'%' IDENTIFIED BY 'newpwd' WITH GRANT OPTION;

以后执行刷新数据库：

flush privileges;

若是要查看用户的权限，能够执行：

> show grants for 'root'@192.168.10.83