[magento] Could not determine temp directory, please specify a cache_dir manually

magento version: 1.5.1

OS: CentOS 5.2

Server: Apache 2.X

MySQL: 5.X

After i uploaded the code and installed magento, it seems that it is running well. But when i visit http://www.mywebsite.com/index.php/admin/catalog_product/index/key/cbe2b4d77f0b3b97de24c4a43443458e/ , i get this error:

Could not determine temp directory, please specify a cache_dir manually 

Thanks to google, finally i found the solution.

Open lib/Zend/Cache/Backend/File.php,

change these code from:

protected $_options = array(

        'cache_dir' => 'null', 

to: 

protected $_options = array(

        'cache_dir' => '/tmp', 

then it is ok now.

Have fun with magento!