代码如下：
<?php
$mysqli = new mysqli('localhost', 'root', '184995511', 'cg_levi');
if ($mysqli->connect_error) {
die('Connect Error (' . $mysqli->connect_errno . ') '
. $mysqli->connect_error);
};
echo 'ok';
如果上面连接地址为'localhost'就会报错，如下：
Warning: mysqli::mysqli(): (HY000/2002): No such file or directory in /mnt/www/cglevi/publichtml/mysql.php on line 2 Connect Error (2002) No such file or directory
将'localhost'修改为'127.0.0.1'之后链接正常
查看了hosts没有问题，如下：
127.0.0.1 localhost
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
/etc/hosts (END)
查看mysql状态，没有问题，如下：
mysql> status;
--------------
mysql Ver 14.14 Distrib 5.6.10, for Linux (x86_64) using EditLine wrapper
Connection id: 860
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.6.10 MySQL Community Server (GPL)
Protocol version: 10
Connection: Localhost via UNIX socket
Server characterset: latin1
Db characterset: latin1
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /var/lib/mysql/mysql.sock
Uptime: 13 hours 13 min 50 sec
Threads: 1 Questions: 11900 Slow queries: 0 Opens: 100 Flush tables: 1 Open tables: 80 Queries per second avg: 0.249
--------------
请问如何解决？
参考这个问题： http://.com/q/1010000000320989
提问之前记得先搜索。
开始的回答有点不严谨，估计也没有解决问题，修改了答案：
问题出现的原因：
当主机填写为localhost时MySQL会采用 unix domain socket连接，当主机填写为127.0.0.1时MySQL会采用TCP/IP的方式连接。使用Unix socket的连接比TCP/IP的连接更加快速与安全。这是MySQL连接的特性，可以参考官方文档的说明4.2.2. Connecting to the MySQL Server：
On Unix, MySQL programs treat the host name localhost specially, in a way that is
likely different from what you expect compared to other network-based programs.
For connections to localhost, MySQL programs attempt to connect to the local server
by using a Unix socket file. This occurs even if a --port or -P option is given to
specify a port number. To ensure that the client makes a TCP/IP connection to the
local server, use --host or -h to specify a host name value of 127.0.0.1, or the IP
address or name of the local server. You can also specify the connection protocol
explicitly, even for localhost, by using the --protocol=TCP option.
这个问题有以下几种解决方法：
- 使用TCP/IP代替Unix socket。即在连接的时候将localhost换成127.0.0.1。
修改MySQL的配置文件my.cnf，指定mysql.socket的位置：
/var/lib/mysql/mysql.sock (你的mysql.socket路径)。
直接在php建立连接的时候指定my.socket的位置（官方文档：mysqli_connect）。比如：
$db = new MySQLi('localhost', 'root', 'root', 'my_db', '3306', '/var/run/mysqld/mysqld.sock')
如果哪里没有说清楚或者说错了，欢迎提出了～～