Write once, read many (WORM) using Linux file system

You can sort of do this with OpenAFS and read-only volumes. It's a lot of infrastructure to install to make it work however and might not meet the requirements.

http://www.openafs.org/

Basically, there is a writeable volume and one or more read-only copies of the volume. Until you release the writeable volume, the read-only copies are unchangeable to clients. Releasing the volume requires admin privileges.

It seems like any solution would require either specialized hardware or a network file system that duplicates the semantics of specialized hardware.