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

今天在測試MySQL的鏈接時候，發現鏈接不經過，並報錯ERROR 2003 (HY000): Can't connect to mysql server on '192.168.10.210' (111) 
測試代碼：

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

谷歌了一下以後，原來是在mysql的my.cnf中有下面一段代碼：

# 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  #這裏默認監聽本地localhost

若是要讓mysql監聽到其餘的地址，能夠將bind-address = 127.0.0.1註釋掉。 
或者將bind-address = 0.0.0.0監聽全部的地址

屏蔽掉以後再次運行代碼又出現：Host '192.168.10.83' is not allowed to connect to this MySQL server 
 
解決方法： 
若是想讓192.168.10.83可以鏈接到本地的這個數據庫，要讓數據庫給其分配權限,登陸mysql，執行:(username 和 password是登陸mysql的用戶名和密碼)

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地址都可以訪問使用mysql，能夠執行下面：(此處是對root用戶受權mysql全部數據庫)

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

若是針對某個特定的用戶test受權某個指定的數據testdb用下面例子中的命令

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

以後執行刷新數據庫：

flush privileges;

若是要查看用戶的權限，能夠執行：

> show grants for 'root'@192.168.10.83