某客户在安装 Magento程序的时候，提示错误 PHP extension "mcrypt" must be loaded.

一般来说，进入ssh，执行 yum -y install mcrypt php-mcrypt 即可安装mcrypt支持，然后service httpd restart 即可

可是，我执行  yum -y install mcrypt php-mcrypt 的时候提示mcrypt 已经安装：

Package php-mcrypt-5.1.6-15.el5.centos.1.i386 already installed and latest version
Nothing to do

于是查看下php的版本：

php -v
PHP Warning:  PHP Startup: mcrypt: Unable to initialize module
Module compiled with module API=20050922, debug=0, thread-safety=0
PHP    compiled with module API=20060613, debug=0, thread-safety=0
These options need to match
 in Unknown on line 0
PHP 5.2.17 (cli) (built: Jan  7 2011 21:18:16)
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies
    with Zend Extension Manager v1.2.2, Copyright (c) 2003-2007, by Zend Technologies
    with Zend Optimizer v3.3.3, Copyright (c) 1998-2007, by Zend Technologies

发现毛病： php版本是5.2，但是php-mcrypt却是5.1版本。难怪有问题。估计是客户在升级到php5.2的时候，没有正确升级好php-mcrypt。

这里ctohome通过下面的命令升级php-mcrypt：

 yum --enablerepo=webtatic --exclude=php*5.3* update -y mcrypt mbstring php-mbstring php-mcrypt

service httpd restart

在测试，一切正常。安装Magento错误PHP extension "mcrypt" must be loaded.搞定。