Linux on System z

Linux on z Systems (or Linux on z for short, and previously Linux on System z) is the collective term for the Linux operating system compiled to run on IBM mainframes, especially IBM z Systems and IBM LinuxONE servers. Similar terms which imply the same meaning are Linux on zEnterprise, Linux on zSeries, Linux/390, Linux/390x, etc. The terms zLinux or z/Linux are also sometimes used, but these terms are discouraged by IBM as they create the implication of an IBM-offered or IBM-distributed version of Linux, which is incorrect. (Further, "zLinux" without the slash is definitely incorrect, as it's software, and software takes a slash: z/VM, z/OS, z/VSE, et al.; hardware does not: z900, z13, et al.)

Linux on z originated as two separate efforts to port Linux to IBM's largest servers. The first effort, the "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 on December 18, 1999, to start today's mainline Linux on z. Formal product announcements quickly followed in 2000, including the Integrated Facility for Linux (IFL) engines. Think Blue Linux was an early mainframe distribution consisting mainly of Red Hat packages added to the IBM kernel. Commercial Linux distributors introduced mainframe editions very quickly after the initial kernel work.

At the start of IBM's involvement, Linux patches for System z included some object code only (OCO) modules, without source code. Soon after IBM replaced the OCO modules with open source modules. Linux on z is free software under the GNU General Public License.

According to IBM, by May, 2006, over 1,700 customers were running Linux on their mainframes.

Virtualization is required by default on IBM z Systems; there is no option to run Linux on z without some degree of virtualization. (Only the very first 64-bit mainframe models, the z900 and z800, included a non-virtualized "basic mode.") 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 z. A hypervisor called z/VM can also be run as the second layer virtualization in LPARs to create as many virtual machines (VMs) as there are resources assigned to the LPARs to support them. KVM on z is another hypervisor option.

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