Restrict PHP access to root folders?

Im making sort of a service where people can upload PHP files and they get their own directory.

Is there a way to prevent any way the PHP can access开发者_如何学C the root of the server? and just stay in the bounderies of its folder?

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The open_basedir directive does just that :

Limit the files that can be opened by PHP to the specified directory-tree, including the file itself.

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The most secure would be to chroot Apache and PHP.