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Linux and mainframes, part 2: Choosing distros and apps

Running Linux on an IBM mainframe doesn't lock users into an IBM-controlled operating system and application world. In fact, Linux expands the mainframe world by bringing open-source into the fold, according to Ingolf Salm, co-author of the new Prentice Hall book, Linux on the Mainframe. In the final part of this two-part interview on Linux and mainframes, Salm provides a guide to choosing Linux distributions and commercial and open-source applications. In part one, Salm described the benefits that virtualization brings to the mix, while his Linux on the Mainframe co-author Maria Eisenhaendler, explained why Linux and the mainframe are a good team.

Should a company that plans to use Linux on the mainframe use a commercial distribution or build its own flavor...

of Linux? Most Linux users need more than just the operating system itself. A Linux production system requires tools and applications. Some of these are supplied with Linux distributions.

While some companies might have the skill to build their own Linux systems (including tools and applications), most of them will turn to commercial Linux distributions as the source for well-defined and stable foundations for their production systems. Distributions for Linux on the mainframe, like all major Linux distributions, contain hundreds of program packages. How does an IT shop select the right Linux distribution for its mainframe?
What the 'right' distribution is for you is highly dependent on your requirements. Choosing which Linux distribution to run in your business really comes down to how close the various distribution options map to your 'style' or 'needs.'

The primary focus doesn't need to be on the Linux kernel; major distributors all deliver an adequate Linux kernel. The differentiation comes from what is included in the distribution.

Many of the applications included in distributions serve general needs that are common to most IT installations, and you are likely to find an interesting set of applications that is useful to you. What, then, is typically included in a mainframe Linux distribution?
Current mainframe Linux distributions usually include applications such as Samba for file and print serving; Sendmail for e-mail services; Apache and Tomcat for Web serving; MySQL as a database server; Network File System (NFS) for file serving; OpenLDAP for directory access; and OpenSSL for implementing secure connections.

These applications provide all that is needed for some server consolidation projects using Linux on the mainframe. For example, many companies have numerous underutilized servers that could be consolidated on the mainframe.

A distributor assures the compatibility of the software packages within a distribution. Therefore, you do not need to worry about the compatibility of an included application with the Linux kernel and the interoperability with other included applications. Applications from your distribution are available with the installation package. The distributor might also provide service and maintenance support for the applications.

While Linux distributions are discussed throughout the book, Chapter 9 discusses how to select a distribution. Can you offer tips for selecting applications that run well on Linux on the mainframe?
Before answering this question, it might be useful to define just what an application is. Is Apache an application, or is it a part of an e-commerce application? In the book, we use different definitions depending on the context. Mostly, we use the term 'applications' with a broad meaning that includes middleware and tools. An application covers all program modules that cooperate to provide a function. Parts of a single application may even be spread across multiple operating system instances on different machines.

Linux on the mainframe gives you great flexibility in how you find and choose your application components -- you can build them yourself, buy them from a software vendor or use open-source software. IBM lists hundreds of applications on their 'ISV support for mainframe servers' Web site.

It is easy to find applications for Linux on the mainframe. Here are some sources: applications that come with your Linux distribution, open-source applications that are not shipped by distributors, and commercial applications from software vendors.

The Internet offers a broad spectrum of applications that goes far beyond what any distribution may offer. In the book, we give starting points for finding open-source applications on the Internet. When should a business consider using a commercial application?
Many useful applications for Linux on the mainframe are commercial applications. These applications are usually subject to regular release cycles, which means better predictability in planning your systems. With commercial applications, you incur license fees and you might also incur dependencies on supporting software, specific distributions, and release cycles. What you gain is maintenance and service support for the product directly from that vendor. Why should businesses consider using open-source applications in mainframe environments?
The value of obtaining open-source applications from the Internet is the great degree of choice and freedom it gives you, including the option to modify the code, as well as the low cost of acquisition. If you are looking for an application to cover very specific requirements in your installation, you are likely to find open-source applications that you can tailor to your needs. What if the application you want is not available?
If an existing application you want to run is not available for Linux on the mainframe today, it may well be available tomorrow. Ask the provider if a port is planned in the near future and register your requirement for such a port. Many software vendors have realized that providing their applications for Linux is an opportunity not to be missed. Porting, especially from Unix to Linux, is relatively easy, and porting tools and documentation are readily available.

You might also want to check for alternative applications. There might be suitable solutions available that are already supported. Moving applications to Linux on the mainframe is an opportunity to upgrade the technologies you are using. Linux applications generally have a reputation for being up to date with the latest standards.

Open-source software is an excellent place to find code for an application tailored to your exact requirements.

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