编译安装了Apache 2.2.17，忘记在httpd.conf中更改默认的user，结果导致httpd无权操作Magento Cache目录。

首先，在CentOS中建立用户www。 

groupadd www
useradd --shell /sbin/nologin -g www www

其次，在Apache配置文件httpd.conf中设置User，Group。 

#
# If you wish httpd to run as a different user or group, you must run
# httpd as root initially and it will switch.
#
# User/Group: The name (or #number) of the user/group to run httpd as.
# It is usually good practice to create a dedicated user and group for
# running httpd, as with most system services.
#
User www
Group www

最后，设置网站文件的用户和用户组为www。 

#假设网站部署在/home/www下
cd /home/www/
chown -R www:www .