First off this week, do you have a recommendation for (or a warning about) a hosting service? We're looking for good management features (particularly for lots of e-mail accounts), good pricing (natch) and good support. Can such a thing be found?

Anyway, last week we mentioned the forthcoming release of Knoppix 3.8.1. Well, it's here. You can find a note about this version at Distrowatch , which also lists the FTP and BitTorrent download links.

As discussed, this release of Knoppix includes UnionFS, a stackable unification file system that merges the updated contents of multiple directories but keeps their original physical content separated.

The UnionFS Web site describes the system as "useful for unified source tree management, merged contents of split CD-ROM, merged separate software package directories, data grids and more. UnionFS allows for any mix of read-only and read-write branches, as well as insertion and deletion of branches anywhere in the fan-out. To maintain Unix semantics, UnionFS handles elimination of duplicates, partial-error conditions and more."

The Knoppix implementation of UnionFS merges the Knoppix RAMdisk with the read-only file system on the boot CD so you can modify any read-only file as if it was writeable.

UnionFS is part of a project called the File System Translator, or FiST . The goal is to address the problem of file system development, a critical (as well as time consuming and expensive) area of operating-system engineering. The FiST site notes: "Even small changes to existing file systems require deep understanding of kernel internals, making the barrier to entry for new developers high. Moreover, porting file system code from one operating system to another is almost as difficult as the first port."

FiST, developed by Erez Zadok and Jason Nieh in the computer science department at Columbia University, "combines two methods to solve the above problems in a novel way: a set of stackable file system templates for each operating system, and a high-level language that can describe stackable file systems in a cross-platform portable fashion."

The idea is that with FiST, a stackable file system would need to be described only once. Then FiST's code-generation tool would compile one system description into loadable kernel modules for different operating systems (currently Solaris, Linux and FreeBSD are supported).