Linux on zSeries

Linux on zSeries (or Linux on System z9) is the preferred collective term for the Linux operating system and Linux software patched to run on IBM mainframe, especially zSeries servers. Other terms with the same meaning include Linux/390, Linux for zSeries, and z/Linux.

=History=

Linux on zSeries originated as two separate efforts to port Linux to IBM s largest servers. The first effort, the [http://www.linas.org/linux/i370-bigfoot.html Bigfoot] project, developed by Linas Vepstas in late 1998 through early 1999, was an independent distribution, and has since been abandoned. IBM published a collection of patches and additions to the Linux 2.2.13 Kernel (computer science) on December 18, 1999, to start today s mainline Linux on zSeries. Formal product announcements quickly followed in 2000, including the Integrated Facility for Linux (IFL) engines.

=Hardware=

IBM zSeries/z9 servers can run mixed workloads, including numerous other operating systems, through the use of Virtualization technology. Both hardware and software co-evolved over decades to support these workloads, and the Linux OS is no exception.

IFLs (Integrated Facility for Linux) are mainframe processors dedicated to running Linux. Microcode restricts IFLs from running traditional workloads, such as z/OS. z/OS software vendors do not typically charge for IFL capacity, and IFL hardware tend to be less expensive than general purpose engines (CPs). Consequently businesses and governments can easily expand their mainframe Linux installations without affecting most of their software license charges. Although Linux can technically operate on both CPs and IFLs, IFLs simply cost less.

Linux on zSeries is available in both 31-bit and 64-bit versions, with the 64-bit versions rapidly gaining popularity as zSeries and System z9 mainframes become more prevalent. The Linux 2.6.x kernel added substantial support for mainframe hardware, although several vendor distributions backportinged 2.6.x patches to the Linux 2.4.x kernel. For example, Linux on zSeries supports ESCON, FICON, SCSI-attached storage devices, and zSeries cryptographic accelerators.

At the start of IBM s involvement, Linux on zSeries included some OCO (object code only) modules, without source code. However, currently Linux on zSeries is completely open source under the GNU General Public License with the lone exception of an optional tape driver OCO module.

=Advantages=

As one of the most scalable platforms for Linux computing, zSeries/z9 has several major advantages. First, companies and governments can consolidate numerous small Linux and PC servers, retaining the benefits of centralizing, but still keeping a multitude of specialized servers thanks to the virtualization support, thereby reducing operating costs. File servers, Web servers, print servers, name/directory servers, and other utility servers are well-suited for this. Second, Linux on zSeries can take advantage of the advantages to mainframes- their reliability and security features, to support continuous business operations. (The zSeries/z9 servers assure that machine instructions execute correctly- e.g.2+2 always equaling 4- using redundant processor execution steps and integrity checking. This execution integrity is automatic and transparent to Linux. Many industries, including financial services, need this unique capability for their Linux applications.) Third, IBM s mainframe customers benefit, like other Linux users, from the vast and growing portfolio of useful software applications, including open source innovations.

zSeries servers start at under $200,000 (zSeries 890 Model 110, U.S. 2004 list price, excluding disk storage), so Linux on zSeries is not appropriate for small businesses with fewer than about 30 Linux servers. However, beyond that threshold Linux on zSeries can become cost-advantageous.

z/OS still has numerous reliability and availability advantages over Linux, so most Linux on zSeries customers run both operating systems and will likely do so for the foreseeable future.

=Environment=

zSeries/z9 servers are capable of multiple levels of virtualization (as the hypervisor itself can be virtualized), including LPARs (flexible partitions). Linux on zSeries can occupy whole partitions — even whole servers. However, most Linux on zSeries customers take advantage of VM (Operating system). z/VM provides virtual machines, with Linux running as a guest operating system under a hypervisor. z/VM dynamically manages processors, memory, and storage on behalf of Linux, carving up a large mainframe into hundreds or even thousands of concurrently operating Linux images. Some other servers support partitions and/or virtual machines, but the zSeries/z9 is one of the best, in its scope, scale, and flexibility, for Linux computing.

Since the Linux kernel tends to assume that it is the sole OS running, that it owns the entire system, including all its memory, z/VM helps tame Linux. It is likely that, over time, the Linux kernel will more closely cooperate with z/VM (and vice versa), to better manage memory use in order to further increase capacity.

=Support=

Like most other versions of Linux, Linux on zSeries is governed by the GPL Free software license. Linux on zSeries Source code is available from numerous groups on a free and equal basis, and architectural support is now part of the main Linux kernel effort. IBM assigns several of its programmers to the community effort, but IBM is by no means the only corporate participant.

Most Linux on zSeries customers, particularly those with business-critical production workloads, purchase a software support contract from commercial Linux vendors such as Novell SUSE Linux or Red Hat. IBM Global Services also offers support contracts, including 24x7 coverage. Most standard Linux software applications are readily available for Linux on zSeries, including popular enterprise software packages such as WebSphere, DB2 and Oracle database databases, and IBM s Java programming language Developer s Kit (JDK). Nearly every open source software package available for Linux is available for Linux on zSeries, including Apache HTTP Server, Samba software, JBoss, PostgreSQL, MySQL, PHP, Python programming language, Concurrent Versions System, GNU Compiler Collection, and Perl, among many others.

=Market outlook=

Linux itself is growing rapidly as of mid-2005, and the Linux on zSeries is no exception. As businesses and governments grow their Linux-based computing infrastructures, large zSeries/z9 servers are more popular. IBM is aggressively promoting Linux on zSeries, and the company is now well-regarded within the Linux community as a defender of open source values; particularly because of its legal battles against the SCO Group. In their 2005 hype report, IT industry analyst firm Gartner cited Linux on zSeries as arguably the leading driver of Linux s adoption among businesses and governments.

Novell SUSE Linux currently has the most popular Linux on zSeries distribution, although Red Hat is close behind. Debian, Gentoo Linux, Slackware, and CentOS are other notable Linux on zSeries distributions. Linux on zSeries distributions borrow from the s390 architecture branch of the Linux kernel.

=Developer resources=

Linux software developers certified for zSeries can appeal to large enterprises. There are few barriers to doing so as IBM offers a no-charge 30-day [http://www-1.ibm.com/servers/enable/site/testdrive/zseries/ Linux on zSeries test drive ], allowing Linux developers of any size access to a live Linux guest running under z/VM for compiling and testing software.

There are at least two software-based mainframe is also available but is not sanctioned for running licensed mainframe operating systems, such as z/OS.

=See also=

*Comparison of Linux distributions *Linux on Power *zAAP *TPF *VSE

=External links=

*[http://www.ibm.com/linux Linux Technology Center at IBM] *[http://www.ibm.com/linux/matrix IBM Software for Linux] *[http://www.theregister.co.uk/2005/03/31/deutsche_bahn_ibm_suse_server_consolidation/ Deutsche Bahn (German Rail) Replaces 300 Intel Servers with One Mainframe] *[http://www.tectonic.co.za/viewr.phpid=580 T-Systems Embraces Linux]