Linux on the mainframe: IFLs and LinuxONE
Mainframe hardware can run ordinary Linux distributions alongside, or instead of, z/OS. Linux usually runs on special processors called IFLs, and IBM sells a Linux-only mainframe line called LinuxONE.
Same hardware, a different operating system
Most of this site is about z/OS, but a mainframe is a general-purpose computer. Since the early 2000s it has also run Linux: the same kernel you meet on servers and in the cloud, compiled for the IBM Z architecture. To the person logged on through SSH it looks like any other Linux server: bash, systemd, package managers, Java, Python, databases and web servers.
What is different is underneath. The Linux system runs on mainframe processors, uses mainframe disk and network adapters, and usually shares a physical machine (a CPC) with other operating systems, each in its own LPAR.
What an IFL is
An IFL (Integrated Facility for Linux) is a mainframe processor core that is enabled to run Linux and the hypervisors that host Linux (z/VM and KVM), but cannot run z/OS. Physically it is the same kind of core as a general-purpose processor. The difference is commercial and configuration-based, much like a zIIP: it exists so that adding Linux capacity does not raise the cost of z/OS software, which is typically charged on general-purpose capacity.
| Processor type | What it runs | Why it exists |
|---|---|---|
| General purpose (CP) | z/OS and everything else | The standard engine; z/OS software pricing is usually tied to this capacity |
| zIIP | Eligible z/OS work such as parts of Db2, Java and some network processing | Offloads specific z/OS work to lower-cost capacity |
| IFL | Linux, z/VM and KVM only | Lets a site add Linux capacity without increasing z/OS software charges |
LinuxONE
LinuxONE is IBM's family of mainframe servers sold for Linux only. They use the same processor technology as the IBM Z machines of the same generation, but every core is an IFL, so they do not run z/OS. Organisations that have no z/OS estate but want mainframe reliability, security features or consolidation density buy LinuxONE; organisations that already run z/OS often add IFLs to their existing IBM Z machines instead.
Distributions
Linux on Z is not a special product. The major enterprise distributions build and support an IBM Z edition:
- Red Hat Enterprise Linux for IBM Z, the base for Red Hat OpenShift on the platform
- SUSE Linux Enterprise Server for IBM Z and LinuxONE
- Ubuntu Server from Canonical
- Community distributions such as Fedora, Debian and openSUSE also publish builds for the architecture
Which distribution and which version a site uses, and which IBM Z hardware generations each supports, is set by the vendor's support matrix. Always check it before planning an upgrade of either the hardware or the operating system.
Why organisations do this
- Consolidation: hundreds of lightly used x86 servers can often run as virtual Linux guests on a much smaller number of IFLs, because mainframes are built to run at very high utilisation.
- Per-core software licences: some database and middleware products are licensed per core, so fewer, busier cores can reduce licence cost. Whether this saves money depends on the vendor's terms.
- Reliability and security: the hardware's redundancy, on-chip cryptography and features such as IBM Secure Execution for Linux (which isolates a guest even from the hypervisor administrators, on supported hardware) appeal to regulated industries.
- Being close to z/OS data: applications that call CICS, Db2 or MQ on z/OS all day can sit on the same machine, a topic for lesson three.
$ uname -m s390x $ lscpu | head -3 Architecture: s390x CPU op-mode(s): 32-bit, 64-bit Byte Order: Big Endian
What does uname -m print on a 64-bit Linux system running on IBM Z?
Show a hint
It is the name of the architecture used in package names and container image platforms.
Show the solution
s390x, the 64-bit IBM Z architecture name used by the Linux kernel and distributions.
Common mistakes
It is the same kernel and the same enterprise distributions, built for another architecture. Linux skills transfer almost entirely; what changes is the hardware layer and the binaries.
IFLs run Linux, z/VM and KVM only. z/OS needs general-purpose processors, with zIIPs for eligible work.
Savings from consolidation depend on each vendor's licensing rules for virtualised and IBM Z environments. Get the licensing team to confirm before building a business case on it.
What you will see at work
- Infrastructure teams may ask you to deploy an application to a Linux guest that happens to live on the mainframe; most of the work is ordinary Linux administration.
- Capacity and finance discussions talk about adding IFLs versus general-purpose capacity, because they are priced differently.
- Banks and governments use LinuxONE or IFLs for consolidated databases, middleware and secure workloads next to their z/OS systems.
Key terms
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