please explain me subtree_check

arun17reddy · 06-14-2010, 11:52 AM

hi can anyone explain subtree_check in detail.

thanx alot in advance...

brucehinrichs · 06-14-2010, 11:57 AM

Try this.

EDIT: From the link above:

Quote:

C7. Why should I disable subtree checking on my NFS server exports?

A. When an NFS server exports a subdirectory of a local file system, but leaves the rest unexported, the NFS server must check whether each NFS request is against a file residing in the area that is exported. This check is called the subtree check.

To perform this check, the server includes information about the parent directory of each file in NFS file handles that are handed out to NFS clients. If the file is renamed to a different directory, for example, this changes the file handle, even though the file itself is still the same file. This breaks NFS protocol-compliance, often causing misbehavior on clients such as ESTALE errors, inappropriate access to renamed or deleted files, broken hard links, and so on.

In the opinion of many, subtree checking causes much more trouble than it saves, and should be avoided in most cases. The subtree_check option is necessary only when you want to prevent a file handle guessing attack from gaining access to files that fall outside the exported part of your server's local file systems. If you need to be certain that noone can access files outside the exported part of a local file system, set up the partitions on your server so that you only export whole file systems.