Halo. I am very confused. Please help me

Background:
I used 4 host to establish a high-availability web server system.
2 Load Balancer + 2 Web Server(installed MySQL Server 5.5). 2 MySQL Server used Multi-Master Replication.
Used "Amoeba" as MySQL Proxy which direct the write statement to a specific MySQL Server.

I can login Amoeba and MySQL Server using MySQL client.
I tried query something in XAMMP on Windows XP. It work!

Installed related software:
MySQL-server-5.5.11-1.rhel5
MySQL-shared-compat-5.5.11-1.rhel5
php53-mysql-5.3.3-1.el5_6.1
MySQL-client-5.5.11-1.rhel5
php53-gd-5.3.3-1.el5_6.1
php53-cli-5.3.3-1.el5_6.1
php53-5.3.3-1.el5_6.1
php53-mysql-5.3.3-1.el5_6.1
php53-common-5.3.3-1.el5_6.1
php53-pdo-5.3.3-1.el5_6.1

What I tried:
yum install php php-mysql
yum install php53 php53-mysql
Compiled php 5.3.6 soruce + MySQL 5.5 Server, Client, Shared, Shared-Compact

Above software installed on different host. And the phpinfo showing MySQL

I doubt something wrong in my php.ini. Used default php configuration.

Thank you for your time.

Check out the log file of MySQL and your web server located in /var/log. That should give you useful information. Using the following function in PHP is a good idea to find out what the error is about:
Write it after the mysql_connect function in your code.

Thank you for your reply. I had tried your suggestion. "Can't connect to MySQL server ...".

My situation: "I could connect to MySQL from the PHP via Apache and MySQL via the MySQL console, and could not connect via the PHP"

But, PHP only can connect to MySQL using mysql_connect("localhost", "root", "password");

I found the problem

Solution:
setsebool -P httpd_can_network_connect=1

Yeah. It's SELinux that many times causes problems but is hidden from the user's perspective, especially in Red Hat systems that is enabled by default.

koosha, Thank you for your help