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Linux on IBM Z,Linux on zSystems, orzLinux is the collective term for theLinux operating system compiled to run onIBM mainframes, especiallyIBM Z, zSystems, andLinuxONE servers. Similar terms which imply the same meaning areLinux/390,Linux/390x, etc. The threeLinux distributions certified for usage on the IBM Z hardware platform areRed Hat Enterprise Linux,SUSE Linux Enterprise Server, andUbuntu.
Linux on IBM Z originated as two separate efforts to port Linux to IBM'sSystem/390 servers. The first effort, the "Bigfoot" project, developed byLinas Vepstas in late 1998 through early 1999, was an independent distribution and has since been abandoned.[1] IBM published a collection of patches and additions to the Linux 2.2.13kernel on December 18, 1999, to start today's mainline Linux on IBM Z.[2] Formal product announcements quickly followed in 2000, including theIntegrated Facility for Linux (IFL) engines.Think Blue Linux was an early mainframe distribution consisting mainly ofRed Hat packages added to the IBM kernel.[3] Commercial Linux distributors introduced mainframe editions very quickly after the initial kernel work. The first lines of mainframes supported by Linux enterprise distributions wereSystem/390 G5, G6, andMultiprise 3000.[4]
IBM manager Karl-Heinz Strassemeyer of Böblingen in Germany was the main lead to get Linux running on S/390.[5]
At the start of IBM's involvement, Linux patches for S/390 included someobject code only (OCO) modules, without source code.[6] Soon after, IBM replaced the OCO modules withopen source modules. Linux on IBM Z isfree software under theGNU General Public License.
According to IBM, as of May 2006[update], over 1,700 customers were running Linux on their mainframes; some examples areNomura Securities,Home Depot, and theUniversity of Pittsburgh.[7]
Virtualization is required by default on IBM Z; there is no option to run Linux on IBM Z without some degree of virtualization. (Only the very first 64-bit mainframe models, the z900 and z800, included a non-virtualized "basic mode".) The first layer virtualization is provided by the Processor Resource and System Manager (PR/SM) to deploy one or more Logical Partitions (LPARs). Each LPAR supports a variety of operating systems, including Linux on IBM Z. Ahypervisor called z/VM can also be run as the second layer virtualization in LPARs. This allows an LPAR to run as many virtual machines (VMs) as can be supported by the resources assigned to the LPAR.KVM on IBM Z is another hypervisor option.
When Linux applications in an LPAR access data and applications in other LPARs, such asCICS,IBM Db2,IMS,Linux, and other mainframe subsystems running on the same physical mainframe, they can utilizeHiperSockets, which are memory-onlyTCP/IP connections. As compared to TCP/IP over standardnetwork interface controllers (NICs, also known as Open System Adapters (OSAs) in mainframes), HiperSockets can improve end-user responsiveness (reduce network latency and processing overhead), security (since there is no network connection to intercept), and reliability (since there is no network connection to lose).[8]
With the zEC12, zBC12, and later models, the HiperSocket concept is extended beyond the physical machine boundary via anRDMA over Converged Ethernet (RoCE) adapter to facilitate a secure and high-speed inter-system communication. Applications in LPAR A in system A can thus use HiperSockets to communicate with applications in LPAR B in system B to ensure the security and performance attributes.[citation needed]
Beginning with Linux kernel version 4.1 released in early 2015, Linux on IBM Z is only available as a64-bit operating system compatible withz/Architecture mainframes. Previously, Linux on IBM Z was also available as a32-bit operating system, with31-bit addressing, compatible with older model mainframes introduced prior to 2000's z900 model. However, the newer 64-bit Linux kernel and 64-bit Linux on IBM Z distributions are still backward compatible with applications compiled for 32-bit Linux on IBM Z. Historically, the Linux kernel architecture designations were "s390" and "s390x" to distinguish between the 32-bit and 64-bit Linux on IBM Z kernels respectively, but "s390" now also refers generally to the one Linux on IBM Z kernel architecture.
Linux runs on standard, general purpose mainframe CPs (Central Processors) as well as IFLs (Integrated Facility for Linux). IFLs are mainframe processors dedicated to running Linux, either natively or under a hypervisor (z/VM or KVM on IBM Z).Microcode restricts IFLs from running "traditional" workloads, such asz/OS, but they are physically identical to other IBM Z processors. IFLs are typically less expensive to acquire from IBM than CPs.[9]
Linux on IBM Z gives the flexibility of running Linux with the advantages offault-tolerant mainframe hardware capable of over 90,000 I/O operations per second[10] and with amean time between failure (MTBF)[11] measured in decades.[12] Using virtualization, numerous smaller servers can be combined onto one mainframe, gaining some benefits of centralization and cost reduction, while still allowing specialized servers. Combining full virtualization of the hardware plus lightweightVirtual Machine containers that run Linux in isolation (somewhat similar in concept toDocker) result in a platform that supports more virtual servers than any other in a single footprint,[13][failed verification] which also can lower operating costs. Additional savings can be seen from reduced need for floor space, power, cooling,networking hardware, and the otherinfrastructure needed to support adata center.[citation needed]
IBM mainframes allow transparent use of redundant processor execution steps and integrity checking, which is important for critical applications in certain industries such as banking.[citation needed] Mainframes typically allowhot swapping of hardware, such as processors and memory. IBM Z provides fault tolerance for all key components, including processors, memory, I/O Interconnect, power supply, channel paths, network cards, and others. Through internal monitoring, possible problems are detected and problem components are designed to be switched over without failing a transaction.[14] In the rare event of failure,firmware will automatically enable a spare component, disable the failing component, and notify IBM to dispatch a service representative. This is transparent to the operating system, allowing routine repairs to be performed without shutting down the system. Many industries continue to rely on mainframes where they are considered to be the best option in terms of reliability, security, or cost.[12]
Like all other versions of Linux, Linux on IBM Z is governed by the GPLfree software license. Complete Linux on IBM Zsource code is available from numerous parties on a free and equal basis, and architectural support is 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 participant.
Though there are no obstacles to running any Linux on IBM Z distribution on an IBM z System, IBM routinely tests three particular Linux on IBM Z distributions:Red Hat,[15]SUSE,[16] and starting in 2015,Canonical'sUbuntu Linux.[17] Other notable Linux on IBM Z distributions includeDebian (upstream for Ubuntu),[18]Fedora (upstream for RHEL),[19]Slackware,[20]CentOS Stream,Alpine Linux[21] andGentoo.[22]
Nearly every free or open-source software package available for Linux generally is available for Linux on IBM Z, includingApache HTTP Server,Samba,JBoss,PostgreSQL,MySQL,PHP,Python programming language,Concurrent Versions System (CVS),GNU Compiler Collection (GCC),LLVM,Perl, andRust,[23] among many others.[24]
Red Hat and SUSE offer mainline support for their distributions running Linux on IBM Z.[25][26] In 2015 Canonical announced plans to offer official support for its distribution starting in early 2016.IBM Global Services also offers support contracts, including 24x7 coverage.[27] Some standard Linux software applications are readily available pre-compiled, including popular closed-source enterprise software packages such asWebSphere,[28]IBM Db2[29] andOracle[30] databases and applications,SAP R/3,SAP ERP,[31] and IBM'sJava Developer's Kit (JDK),[32] to name only a few.
IBM offers resources to developers wishing to target Linux for z:
Linux on IBM Z supportsUnicode andASCII just like any other Linux distribution—it is not anEBCDIC-based operating system.[37] However, for convenience, Linux is able to read kernel parameters in EBCDIC. z/VM takes advantage of this capability.
Porting Linux applications to Linux on IBM Z is fairly straightforward. Potential issues includeendianness (Linux on IBM Z is big-endian) and reliance on non-portable libraries, particularly if source code is not available.[38] Programs can be easilycross compiled to z/Architecture binaries on non-mainframe Linux systems.[39]
There are at least three software-based IBM Z mainframeemulators.
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