How to enable shell_exec() function in CentOS 5.6?

I am using CentOS 5.6.

When I google to find the answer about how to enable shell_exec() in CentOS 5.6 they answer as the following:

# nano /etc/php.ini

remove shell_exec from the disable_functions list. But in my php.ini file shows the following开发者_运维百科:

disable_functions = 

How can I enable shell_exec() function in CentOS 5.6?

Make sure your SELinux is disabled.

Disable safe_mode and shell_exec should be available.

create a script contains the following

<?php
phpinfo();
?>

and see if there is other php.ini files

I found this in the Internet: disable_functions = ""