By Timothy Prickett Morgan

IBM Corp has posted an early prototype release of its forthcoming implementation of Linux for its S/390 mainframes. The basic information about the prototype is available at http://oss.software.ibm.com/developerworks/opensource/linux390. This site contains the basic specs for Linux for S/390, a link to the GNU Linux site (www.opensource.com) where you can download the regular open source C code that comprises Linux. The DeveloperWorks site then includes the compiler tools and S/390 extensions and patches that lets the Linux kernel run on S/390 processors and talk to S/390 peripherals.

IBM is offering the S/390 network drivers as object code, but the various C debuggers and compilers, as well as the extensions that make Linux work on S/390s, are at this point available as open source. IBM Germany is offering very limited technical support for the project, and the company has warned prospective installers that Linux for S/390 is not yet an IBM operating system with technical or usage support and that customers are pretty much on their own.

Linux for S/390 will run on any 9672 mainframe with a G2 series or higher processor, as well as on the low-end Multiprise 2000 and 3000 servers. It can run as a single system image, within a S/390 hardware logical partition (LPAR) or within a VM/ESA guest partition. (We had been told about the VM support and had only heard speculation about the LPAR and single image S/390 support; in effect, Linux has the same kinds of support as MVS ever did with these three kinds of implementations.) That said, it does have lots of limitations thus far. VM provides support for up to 64 virtual processors on a machine (what we usually call a partition), but the Linux for S/390 only supports 32 virtual processors.

The Linux for S/390 extensions take full advantage of the symmetric multiprocessing (SMP) capabilities of the S/390 line, and offer support for IEEE floating point hardware in the G5 and G6 servers that have it and provide software emulation for the G2 through G4 servers that don’t. Linux for S/390 supports parallel and ESCON channels and the 3480 and 3490 tapes and 3380 or 3390 disks that they attach to.

The prototype release supports Token Ring, Ethernet and Fast Ethernet LAN cards, with a maximum of 16 cards per S/390 mainframe. It also supports IBM’s Open Systems Adapter (OSA 2) networking cards. The extensions for S/390 Fast Ethernet cards has not been tested at all, so be wary. The NFS implementation for the prototype has not been tested either. Customers who want to install Linux on their machines have to start with OS/390, VM/ESA or VSE/ESA and have TCP/IP installed.

Linux for S/390 requires at least 64 MB of main memory. It is unclear if the Linux install creates a dual-boost mainframe, or if it completely overwrites the native IBM operating system when it is done.