php无法连接数据库的解决办法总结：
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()，用浏览器打开如图:
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 -penter password: welcome to the mysql monitor. commands end with ; or \g.your mysql connection id is 8server 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 itsaffiliates. other names may be trademarks of their respectiveowners.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 wrapperconnection id: 8current database: current user: root@localhostssl: not in usecurrent pager: lessusing outfile: ‘‘using delimiter: ;server version: 5.7.11 mysql community server (gpl)protocol version: 10connection: localhost via unix socketserver characterset: utf8db characterset: utf8client characterset: utf8conn. characterset: utf8unix socket: /tmp/mysql.sockuptime: 8 days 15 hours 1 min 17 secthreads: 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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以上就是php无法连接数据库的详细内容。