I know of a legacy hosting solution that uses shared disks, but they also use a chroot wrapper for the sftp access to make sure a misuse of chmod doesn't leak d

I know of a legacy hosting solution that uses shared disks, but they also use a chroot wrapper for the sftp access to make sure a misuse of chmod doesn't leak data to other customers. Allowing executable code (CGI, PHP) in such an environment is just a recipe for trouble.