Magento Filesystem Permissions
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This article will give an idea about file and folder permissions required by Magento.
If you are not familiar with UNIX style permissions please read one of the articles found here:
Magento is a web application, or set of scripts, which are interpreted by a PHP executable, which in it’s turn is invoked by a web service process (ex. apache).
Magento will have as much access permissions to the file system as the user under which PHP executable was invoked.
If apache is configured to run PHP using mod_php module, then Magento will be run under same user apache runs (ex. apache, nobody)
If apache is configured to use suEXEC (http://httpd.apache.org/docs/1.3/suexec.html) or suPHP (http://www.suphp.org/) then it will run under the same user you use for FTP or shell access. This will be possible only with CGI or FCGI configuration.
During normal operation of Magento store only 2 folders need to be writable