There is no punch line
by Pete Birkinshaw cc by 2.0
Back in the day, IBM mainframes were the places where the big boys used to go to play. Those behemoths of a long gone age are still around. Safely tucked away in the basements of banks and universities without any chance of us mere mortals to have a peak at them. The hardware is insanely expensive and software is only available on a per cpu and year license no law abiding citizen can pay. A few years back, I had the privilge to see an IBM zSeries mainframe up close at CEBIT. It was quite a sight. Huge disc arrays, dozens of processors, some of them only dedicated to I/O or running java vm instructions with specialized intstruction sets. And all of that packed in huge refrigerator sized black units with a power supply that could darken a whole city block.
Some very smart people wrote an emulator for IBM mainframe hardware. It's aptly called hercules. With it, you can emulate big iron hardware from s/360 up to zSeries. And, as any good software, it's open source. So you can tinker with it without having to cough up a few 100k(sic!). Now, this is all well and good. But what about the software? Sadly, up to date mainframe os are still not affordable for hobbyists. But IBM has released ancient versions of some of their systems. In this post, I will focus on one of IBM's most famous mainframe systems, VM.
In todays terms, VM would be best described as equivalent to Xen and its brethern. It is a hypervisor that runs on the bare metal and manages resources for other os instances. It's main user interface is the ominous cp, which is shorthand for control programm. With it you can start up new instances of vm and assign resources like virtual disks or printers to them. Like inception! And all of that was possible back in the 80s. So, to reiterate, IBM was able to do todays hot stuff with their custom hard- and software decades ago.
As there is an emulator and some old free software and its possible to run that on your home computer; let's get this show on the road, shall we? First, follow this simple steps: Install hercules with your package manager of choice. Download images from here. Install a 3270 compatible terminal application. Follow the intructions in point 2. The steps in Point 2 will get you the desired results, but in a voodoo kind of way. Repeat strange incantations on the console, weave a dead chicken and then, maybe, success. If you don't care about the technicalities of the installation process(btw, you should care!), skip to the next topsection; because geek stuff will follow.
The cfg file for hercules is mostly kosher, you just need to remind it that its running as a s370. That's what the archmode line is for. Next, there is a funky list of device numbers and device types. The numbers are what the s370 ueses to enumerate your devices by, the're going to be important later on. The device types are much more interesting:
Connect into hercules via telnet, and you'll be prompted with a command line about the time; answer no. Cold boot the machine. To the next question answer enable all, this will enable all peripheral devices connected to your hercules instance. You can now connect to your own vm/370 system with a 3270 client. To login, type logon maint; CPCMS. after that you should see something like this:
DASD 190 LINKED R/W; R/O BY OPERATOR DASD 194 LINKED R/W; R/O BY OPERATOR LOGON AT 21:44:45 PST FRIDAY 04/26/13Congratulations, you just logged into a mainframe os! Now. what to do with this? You will be presented with a vm running the cp program. You can't do much interesting with so load the cms operating system in your vm: ipl(Initial Program Load) cms; This will get you a simple single user os. For starters, try edit, list * * *, msg op yo mama or set rdymsg smsg. Now, pull out your trusted vm/370 operators manual and cms command reference and have fun!