What should I do if php and mysql cannot connect?

php与mysql连接不上的解决办法：1、获取当前配置信息；2、获取MySQL socket路径；3、重新配置PHP，打开【php.ini】修改【mysql.default_socket】；4、重启nginx或者apache。

php与mysql连接不上的解决办法：

1、获取当前 mysql.default_socket、mysqli.default_socket、pdo_mysql.default_socket 配置信息

建立一个 PHP 文件, 显示 phpinfo():

用浏览器打开:

在此页面，找到mysql.default_socket、mysqli.default_socket、pdo_mysql.default_socket信息:

2、获取 MySQL socket 路径

通过控制台进入 MySQL, 输入命令: STATUS, 查找 UNIX socket 值

#mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \\g.
Your MySQL connection id is 8
Server version: 5.7.11 MySQL Community Server (GPL)
Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type ‘help;‘ or ‘\\h‘ for help. Type ‘\\c‘ to clear the current input statement.
mysql> STATUS
--------------
mysql  Ver 14.14 Distrib 5.7.11, for osx10.9 (x86_64) using  EditLine wrapper
Connection id:        8
Current database:    
Current user:        root@localhost
SSL:            Not in use
Current pager:        less
Using outfile:        ‘‘
Using delimiter:    ;
Server version:        5.7.11 MySQL Community Server (GPL)
Protocol version:    10
Connection:        Localhost via UNIX socket
Server characterset:    utf8
Db     characterset:    utf8
Client characterset:    utf8
Conn.  characterset:    utf8
UNIX socket:        /tmp/mysql.sock
Uptime:            8 days 15 hours 1 min 17 sec
Threads: 2  Questions: 21  Slow queries: 0  Opens: 114  Flush tables: 1  Open tables: 0  Queries per second avg: 0.000
--------------

3、这时候, 你对比 mysql.default_socket、mysqli.default_socket、pdo_mysql.default_socket 和 通过 MySQL UNIX socket 发现不一样, 这就是 mysql_connect(); 警告的原因: PHP 配置 mysql 有问题.

4、重新配置 PHP, 打开php.ini修改mysql.default_socket、mysqli.default_socket、pdo_mysql.default_socket 的值为: /tmp/mysql.sock

pdo_mysql.default_socket=/tmp/mysql.sock  
mysql.default_socket=/tmp/mysql.sock  
mysqli.default_socket=/tmp/mysql.sock

或者修改my.cnf的socket：

[client]  
socket=/tmp/mysql.sock  
  
[mysqld]  
socket=/tmp/mysql.sock

5、重启nginx或者apache 

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