php 不能连接数据库 php error Can't connect to local MySQL server

测试的php文件 
<?php 
$link=mysql_connect('localhost','root','zz') or die(mysql_error()); 
mysql_select_db('test') or die('no db'); 
mysql_query('SET NAMES utf8'); 
echo 99; 
?> 
运行后报错 
Can't connect to local MySQL server through socket '/tmp/mysql.sock' 
但在 命令行中能进入mysql 
[root@localhost local]# mysql -u root -p 
Enter password: 
Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 3Server version: 5.5.2-m2 Source distribution 
Type 'help;' or '\h' for help. Type '\c' to clear the buffer. 
mysql> 
解决办法 
chown -R root /usr/local/mysql 
chgrp -R mysql /usr/local/mysql 
chown -R root /usr/local/mysql/bin 
chgrp -R mysql /usr/local/mysql/bin 
chgrp -R mysql /var/lib/mysql 
chmod 777 /var/lib/mysql 
chown -R root /var/lib/mysql/mysql 
chgrp -R mysql /var/lib/mysql/mysql 
chmod 777 /var/lib/mysql/mysql 
chown -R root /var/lib/mysql/mysql/* 
chgrp -R mysql /var/lib/mysql/mysql/* 
chmod 777 /var/lib/mysql/mysql/* 
chmod 777 /usr/local/mysql/lib/mysql/libmysqlclient.a