mysqli不能使用localhost，请问这是怎么回事？

Question

代码如下：
$mysqli=newmysqli('localhost','root','184995511','cg_levi');
if($mysqli->connect_error){
die('ConnectError('.$mysqli->connect_errno.')'
.$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):Nosuchfileordirectoryin/mnt/www/cglevi/publichtml/mysql.phponline2
ConnectError(2002)Nosuchfileordirectory
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：
127.0.0.1localhost
::1localhostlocalhost.localdomainlocalhost6localhost6.localdomain6
/etc/hosts(END)
查看mysql状态，没有问题，如下：
mysql>status;
--------------
mysqlVer14.14Distrib5.6.10,forLinux(x86_64)usingEditLinewrapper
Connectionid:860
Currentdatabase:
Currentuser:root@localhost
SSL:Notinuse
Currentpager:stdout
Usingoutfile:''
Usingdelimiter:;
Serverversion:5.6.10MySQLCommunityServer(GPL)
Protocolversion:10
Connection:LocalhostviaUNIXsocket
Servercharacterset:latin1
Dbcharacterset:latin1
Clientcharacterset:utf8
Conn.characterset:utf8
UNIXsocket:/var/lib/mysql/mysql.sock
Uptime:13hours13min50sec
Threads:1Questions:11900Slowqueries:0Opens:100Flushtables:1Opentables:80Queriespersecondavg:0.249
--------------
请问如何解决？