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Linux File System Structure
Tuesday, July 04 2006 @ 05:10 PM EDT

In the previous article on STREAMS, LiS, and Caldera's Netware for Linux, I mentioned the book, "Special Edition - Using Caldera OpenLinux," written by several Caldera employees in 1999. As it happens, the same book has a section on "The Linux File System Structure." As you will recall, SCO's expert, Dr. Thomas Cargill, has opined that "Linux is a substantial copy of UNIX System V Release 4 ("SVr4") because it appropriated the essential structure of UNIX by incorporating (1) many of the "system calls" in SVr4; (2) the SVr4 file system; (3) the ELF format; and (4) the Streams communication module. (Id. at 3-4.)." On that basis, SCO is claiming copyright infringement.

I think STREAMS was pretty much knocked off the list by the evidence we found for that article. What about the structure of file systems? Was Caldera aware back in 1999 that the Linux file system resembled Unix?

Here's what the book says on that point:

The Linux File System Structure The Linux file system is very similar to the standard UNIX file system layout, but of course there are some differences. The key to understanding the Linux file system is to first understand the underlying structure.... The Linux directory structure, which is very similar to UNIX or DOS, is designed as a tree hierarchy....

Linux File System Standard (FHS)

The OpenLinux file system hierarchy is based on, for the most part, the File System Hierarchy Standard (FHS). In the Fall of 1993, an effort began to restructure the file and directory layout of Linux. This project began as the File System Standards, or FSSTND, project. After several iterations as the FSSTND project, the scope was widened to include issues that were general to other UNIX-like operating systems. In view of this expanded focus, the project was renamed the File System Hierarchy Standard (FHS).

Many people have contributed to this effort, but the primary person behind it is Daniel Quinlan. As of this writing, the most current version of the FHS documentation was version 2.0, dated October 26, 1997. It can be obtained from Dan also currently serves as the chairman of the steering committee for the Linux Standard Base group to develop and promote a set of standards that increase the compatibility between Linux distributions.

So Caldera knew at least in 1999 that the two file systems' structures were similar, and it worked to make OpenLinux precisely Unix-like. (FHS.) Of course, the entire world knew, as IBM points out in its Reply Memorandum in Support of Motion to Confine SCO's Claims to, and Strike Allegations in Excess of, the Final Disclosures, (footnote 4) what Linux's file system was like from its inception:

...SCO claims that the Linux file system infringes SCO’s alleged copyrights. Through Mr. Cargill, SCO complains that the Linux file system has characteristics similar to the file-system of UNIX System V, such as hierarchical files, a single tree of directories and no imposed structure. These have been features of Linux since its inception, much like wheels, doors and brakes have long been features of a car.

Whatever Linux does, it does it in broad daylight. Caldera not only could have gone to look on the Internet, it distributed its own distribution of Linux. It knew precisely that Linux has file-system features similar to those of UNIX System V. Caldera not only didn't sue or protest, it supported LSB strongly, and as you can see in this article from 2002, Caldera OpenLinux 3.1.1 was LSB certified. Here's SCO's press release about it, then calling itself Caldera International, Inc. I think seeking LSB certification would qualify as a mistake, from the standpoint of now wanting to sue over file system structure. The time to sue was back in 1999, when the Caldera employees noted the similarity between Unix and Linux, or earlier when Linux was being developed in the open air on the Internet. Instead, Caldera joined the Linux Standard Base (LSB) Project, which was "an attempt to define the common core of components that can be expected to be found in any 'Linux' system," as this joint announcement, signed by Caldera's then-CEO Ransom Love among many others, expressed it in 1998:

The signers of this proposal are most of the leading commercial Linux distributions, board members of Linux International, and key personnel like Linus Torvalds, the creator of Linux. We propose a set of goals and the organization for this project, and invite all other Linux distributions to join us in planning the project and carrying it out.

The "base system" is the set of programs, libraries and files that are essential to every Linux system. These objects and their related file formats play a supporting role for every application. Examples of this include (but are probably not limited to) the C library, the format and placement of system files, and other necessary interfaces. Linux distributions traditionally do not distinguish themselves on these interfaces, they distinguish themselves in other categories, such as the applications on their system, quality and ease of installation, and quality and ease of systems administration as well as support for users. Linux distributions should maintain the base system collectively, as the kernel is maintained, rather than individually.

The Linux Standard Base project will provide a vendor-neutral standard, backed by source code, upon which to build Linux distributions, much as the Linux kernel project provides a single kernel that is shared by all distributions. This standard base will be distributed as a reference platform from which Linux distributions may be derived and which application producers may use for testing, but it will _never_ be targeted to be an end-user solution in itself, as that is the role of the Linux distributions that incorporate the standard.

The application of the standard will be that any program that runs successfully on the reference platform can be expected to run on all Linux systems. If they don't, the distribution creator must either fix a problem with their own distribution, or convince us that there's a bug in the sample distribution which violates the standards. This is not intended to prohibit distributions from making their own extensions to the base system, or even to use different source code from what is supplied in the reference platform - it's only meant to provide a common set of features that will be known to exist on every Linux system which ISVs can depend on. Participation in the base standard will assure the distributions of compatibility with each other for the set of applications that depend only on the files and libraries in the reference platform. As time passes, the standard will expand to include most of the files and libraries upon which a commercial application might depend.

The Linux Standard Base System will be 100% compliant with the Open Source Definition. This assures all distributions that they can derive from it without concern over licensing problems for themselves or their users. Development will be carried out in the public, with anonymous access to the CVS archive and the developer mailing lists. The core group will be a mix of high-quality developers from the Linux community and the staff of commercial distributions, with an organization similar to the tremendously successful Linux kernel development team. Attention will be paid to standards such as POSIX and the FHS (the successor to the Linux Filesystem Standard). However, the project goes far beyond the utility of these standards, because rather than produce only paper documents, it will provide a complete implementation of the standard, ready to be integrated into Linux distributions or used as a reference platform for application developers. This will provide the Linux distributions with improved time-to-market, lower cost, and much less duplication of effort than a paper standard which is defined to fully take into account side effects, undocumented issues, etc....

We, the undersigned, endorse this proposal, and ask that other distributions and ISVs also join us to help further define this proposal and then to help implement it:

Linus Torvalds, Creator of Linux

Jon A. Hall, Executive Director, Linux International

Bruce Perens, Director Linux International, proposed Project Leader

Ransom H. Love, Director Linux International, General Manager, OpenLinux Division, Caldera, Inc.

Roland Dyroff, Director Linux International, S.u.S.E. Linux....

As you can see, both Caldera and SuSE joined with Linus in working on this project. And in Caldera's old documentation for OpenLinux, in Chapter 2, The Linux Development Environment, it told the world this (actually, it still is, because the document is still available on its website to this day:

LSB, the Linux Standard Base, is a pending standard aimed at enhancing application portability across Linux systems; this is discussed more later in this chapter. At the time of publication, the LSB standard has not been officially released so no operating system can legitimately claim conformance to it, but many changes have been made to OpenLinux 3.1 to match dictums that seem highly likely to be in the final LSB standard.

Most software that you develop needs to be packaged and productized for installation on production systems, and Chapter 8 gives an overview of the facilities used for this. Any software you release should include documentation. OpenLinux includes several documentation frameworks you can use, all of which are extensible. Chapter 8 also includes information about how to add your documentation to the appropriate framework....

2.4. Linux Standards Base (LSB)

The Linux Standards Base (LSB) is an industry-wide initiative to define an application standard for all Linux distributions. Major components of the LSB include the Linux kernel, GNU software, and XFree86. When LSB is completed, an application that is built and packaged to conform to LSB can be installed and run on any LSB-compliant system.

LSB is done under the auspices of the Free Standards Group (, who has also produced the Linux Development Platform Specification (LDPS) as an interim standard that can enhance application portability that is being developed now, before LSB is completed.

For more information and to access preliminary versions of the LSB test suites, go to the web page.

2.4.1. LSB Modifications in OpenLinux 3.1

Modifications have been made in OpenLinux 3.1 to conform to what we expect the final LSB specification to define. Caldera does not claim LSB conformance for OpenLinux 3.1 in any way, but we expect that these changes will smooth the transition to LSB-conformant releases.

In 2000, Caldera also joined, along with IBM, SUSE, Red Hat, oldSCO, and the Open Group, the Free Standards Group. What was that? This press release explains:

Free Standards Group

Linux Standard for Software Development Moves Closer to Reality; Linux Standard Base and Linux Internationalization Initiative Incorporate, Gain Support from All Segments of Industry

Business Editors/High-Tech Writers

SANTA CLARA, Calif.--(BUSINESS WIRE)--May 8, 2000--The Linux Standard Base (LSB) and Linux Internationalization Initiative (LI18NUX) announced today that they have incorporated under the name Free Standards Group. The newly formed Free Standards Group was organized to accelerate the use and acceptance of open source technologies through the application, development and promotion of interoperability standards for open source development.

The Free Standards Group has received endorsements from a growing number of industry corporations as well as from public interest groups such as the Debian Project. These milestones move the group significantly closer to its goal of creating a single Linux standard.

The Free Standards Group will draw upon its LSB and LI18NUX roots to ensure that the Linux operating system does not fall victim to fragmentation, breaking into multiple versions, each of which is supported by only selected applications. To prevent that, the Free Standards Group's members are promoting a specification, which, when implemented, will mean that any LSB-compliant application will run successfully on any LSB-compliant Linux distributions. While sensitive to the idea that Linux development should not be stifled, the group is working to define a common subset of Linux that will work for everyone, regardless of distribution.

With its incorporation and its commitment from key players in the industry, the Free Standards Group will be able to place additional resources behind the LSB and LI18NUX.

"The Free Standards Group's efforts will be an important component of the continued success of open source," said Linus Torvalds, Linux creator. "Standards such as the LSB and Li18nux help bring different companies and groups together to solve common problems and will help to advance Linux in a good way."

Daniel Quinlan, chair of the standards group, commented, "Our progress over the last few months has been significant. Key companies and organizations are lining up behind us and the resources and funding we need to achieve our goals are coming in place. We have everything we need to move forward quickly in increasing compatibility among Linux and other open source distributions and in helping to support software vendors and developers to port and write software for open source such as Linux."

Members of the Free Standards Group's list of supporters include:

Atipa Linux Solutions
Caldera Systems
Corel Corporation
The Debian Project
Delix Computer
Enhanced Software Technologies, Inc.
Linux for Power PC
Linux Professional Institute
Metro Link
Open Group
Red Hat, Inc.
Software in the Public Interest, Inc.
Sun Microsystems
SuSE Linux AG
VA Linux Systems

About the Free Standards Group

The Free Standards Group is a nonprofit corporation organized to accelerate the use and acceptance of open source technologies through the application, development and promotion of interoperability standards. It encompasses the Linux Standard Base ( and the Linux Internationalization Initiative (

The Linux Standard Base was formed in 1998 to develop and promote a set of standards that will increase compatibility among Linux distributions and enable software applications to run on any compliant Linux system.

The Linux Internationalization Initiative is focused on software and application portability and interoperability in the International context.

To learn more about the Free Standards Group, please visit our web site at

Quotes from Supporters of the Free Standards Group

"First, a philosophical question. Is there freedom in restriction? In this case, yes. By supporting the Free Standards Group, Linux distributors are free to add unique value to Linux without breaking applications. We free developers to reach a broader audience. And most important, customers are free to purchase Linux solutions that fit their needs without fear that their applications will have compatibility problems." Ransom Love, President and CEO, Caldera Systems ...

Now The SCO Group wishes to turn around and sue members of this very group for following the very standards Caldera helped to establish and encouraged developers to adopt. I think you can figure out for youselves how likely it is that such a strategy will fly in any courtroom. If you were on the jury, what would you be thinking? That's exactly what any judge or jury will be thinking also.

Further, if you look on page 21 of the Caldera OpenLinux book, you find this:

This is what makes Linux such a wonderful operating system. It is open, it is available to everyone, and nobody can steal it or make it proprietary.

Developers and vendors and end users no doubt relied upon Caldera's representations that Linux was not only free to use, it was safe to do so.

While you are at Caldera's documentation site, you might like to check out Caldera's page on UnixWare's standards conformance (or Google's cache, because it is faster.) What do we see on the list, among other things? ABI, ELF, and COFF. SCO Group just can't win for losing. Doesn't anybody there know about Caldera? It's like SCO had a lobotomy or a stroke or something and has lost its longterm corporate memory.

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