Jump to content

Linux on IBM Z

From Alfawiki
Linux on IBM Z
Company typeOperating system variant
IndustryInformation technology
Founded1999
Headquarters
International
ProductsLinux distributions for IBM Z mainframes

Linux on IBM Z, also known as Linux on zSystems or zLinux, denotes the Linux operating system specifically compiled for IBM mainframe platforms, including IBM Z, zSystems, and LinuxONE servers. Comparable designations are Linux/390 and Linux/390x. The three Linux distributions officially certified for IBM Z hardware are Red Hat Enterprise Linux, SUSE Linux Enterprise Server, and Ubuntu.

History

The development of Linux on IBM Z originated from two distinct initiatives aimed at porting Linux to IBM's System/390 mainframes. One of these was the "Bigfoot" project, led by Linas Vepstas between 1998 and 1999, which was an independent distribution that was eventually discontinued. IBM contributed patches to the Linux 2.2.13 kernel in December 1999, marking the beginning of mainstream Linux support on IBM Z. This was followed by official product launches in 2000, including the introduction of Integrated Facility for Linux (IFL) processors. Early distributions such as Think Blue Linux integrated Red Hat packages with the IBM kernel. Commercial Linux providers rapidly released mainframe-compatible editions supporting systems like the System/390 G5, G6, and Multiprise 3000.

The initiative to run Linux on S/390 was overseen by IBM manager Karl-Heinz Strassemeyer. Initially, some patches contained object code only (OCO) modules without accompanying source code; however, these were soon replaced with fully open source components. Linux on IBM Z is distributed as free software under the terms of the GNU General Public License.

By 2006, IBM reported that more than 1,700 customers had adopted Linux on their mainframe systems, including notable organizations such as Nomura Securities, Home Depot, and the University of Pittsburgh.

Virtualization

On IBM Z platforms, virtualization is a prerequisite for running Linux; it cannot operate independently without it. The primary virtualization infrastructure is provided by the Processor Resource and System Manager (PR/SM), which enables the creation of multiple Logical Partitions (LPARs). Each LPAR can host various operating systems, including Linux on IBM Z. Within these LPARs, a hypervisor called z/VM can be deployed as a secondary virtualization layer to manage numerous virtual machines (VMs) based on assigned resources. An alternative hypervisor option available is KVM on IBM Z.

Communication between Linux workloads in separate LPARs is facilitated by HiperSockets—memory-based TCP/IP connections that deliver lower latency, enhanced security, and greater reliability compared to standard network interfaces. Starting with models such as zEC12 and zBC12, HiperSockets functionality has been extended beyond a single server through RDMA over Converged Ethernet (RoCE) adapters, allowing secure and high-speed communication between LPARs across distinct physical machines.

Hardware

Since the release of Linux kernel version 4.1 in 2015, Linux on IBM Z operates solely as a 64-bit system compatible with z/Architecture mainframes. Earlier kernels supported 32-bit operation for legacy systems but the current 64-bit kernel maintains backward compatibility with 32-bit applications. Historically, "s390" referred to the 32-bit kernel architecture while "s390x" denoted 64-bit; presently, "s390" generally identifies the architecture for Linux on IBM Z kernels.

Linux runs on both conventional mainframe Central Processors (CPs) and Integrated Facility for Linux (IFLs)—processors dedicated exclusively to Linux workloads that cannot execute traditional systems like z/OS but are physically identical to CPs. IFL processors typically offer a more economical acquisition cost from IBM.

The fault-tolerant hardware underlying Linux on IBM Z supports over 90,000 input/output operations per second and features mean time between failures measured in decades. Virtualization enables consolidation of multiple smaller servers onto a single mainframe platform, lowering costs while preserving specialized workload capabilities. By combining comprehensive hardware virtualization with lightweight z/VM container technology, this platform supports more virtual servers per unit area than any other system, reducing operational expenses related to floor space, power consumption, cooling requirements, networking equipment, and data center infrastructure.

IBM mainframes provide transparent redundancy through processor execution monitoring and integrity verification essential for sectors such as banking. They allow hot-swapping of components including processors and memory modules. The IBM Z architecture guarantees fault tolerance across processors, memory modules, I/O interconnects, power supplies, channel paths, and network interfaces. Internal diagnostics detect faults early; defective components are replaced seamlessly without interrupting ongoing transactions. Firmware automatically activates spare parts and alerts IBM service personnel when maintenance is necessary, enabling repairs without downtime. This high level of reliability and security makes mainframes a preferred choice across numerous industries.

Support

Linux on IBM Z operates under the GPL free software license, with full access to source code provided by various contributors. The core Linux kernel incorporates architectural support directly, with IBM supplying multiple developers while not having sole control over the development process.

IBM consistently validates three leading Linux on IBM Z distributions: Red Hat Enterprise Linux, SUSE Linux Enterprise Server, and since 2015, Canonical's Ubuntu Linux. Additional significant distributions include Debian (the upstream for Ubuntu), Fedora (the upstream for RHEL), as well as Slackware, CentOS Stream, Alpine Linux, and Gentoo.

The majority of open-source applications available for Linux are also compatible with Linux on IBM Z, encompassing enterprise-grade software such as Apache HTTP Server, Samba, JBoss, PostgreSQL, MySQL, PHP, Python, GCC, LLVM, Perl, and Rust.

Red Hat and SUSE maintain official support for their IBM Z distributions. Canonical initiated formal support in early 2016. IBM Global Services delivers support agreements offering round-the-clock assistance. Pre-built standard and enterprise packages include IBM WebSphere, IBM Db2, Oracle databases and related applications, SAP R/3 and SAP ERP solutions, alongside IBM’s Java Developer Kit (JDK).

Developer resources

IBM offers a variety of tools and services for developers working with Linux on IBM Z:

  • The Linux Test Drive program provides a complimentary 30-day virtual machine running Linux on IBM Z.
  • IBM Systems Application Advantage for Linux (Chiphopper) helps developers build and distribute cross-platform Linux applications.
  • The Community Development System for Linux on IBM Z (CDSL) supports open source contributors in adapting software to run on Linux for System z.
  • The Linux Remote Development Program is a paid service that extends developer support capabilities.

Linux on IBM Z supports both Unicode and ASCII character encodings similar to other Linux variants; it is not based on EBCDIC encoding but can interpret kernel parameters in EBCDIC format for convenience, a feature leveraged by z/VM.

Porting software to Linux on IBM Z is typically straightforward. However, challenges arise from endianness differences—Linux on IBM Z uses big-endian format—and reliance on non-portable libraries without available source code. Cross-compilation targeting z/Architecture binaries can be performed on non-mainframe Linux platforms.

Emulators

Prominent emulators for IBM Z mainframes include:

  • FLEX-ES by Fundamental Software, a commercial product supporting up to 31-bit addressing.
  • The open source Hercules emulator, capable of running Linux on IBM Z and operable even within Linux on System z environments.
  • IBM’s Rational Development and Test Environment for z (RDTz), launched in 2010, provides a constrained execution setup on x86 hardware aimed at application development. It features z/OS with middleware support and accommodates Linux on IBM Z; however, licensing restricts its use for final pre-production builds or performance stress testing.

See also

External links

Retrieved from "https://www.alfawiki.org/index.php?title=Linux_on_IBM_Z&oldid=28087"