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08 Apr 2012

VM/370 on Linux with the Hercules Emulator

For no particularly good reason, I decided I wanted to play around with IBM VM earlier this weekend. Although this would seem on its face to be fairly difficult – VM/370 is a mainframe OS, after all – thanks to the Hercules emulator, you can get it running on either Windows or Linux fairly easily.

Unfortunately, many of the instructions I found online were either geared towards people having trouble compiling Hercules from source (which I avoided thanks to Ubuntu’s binaries), or assume a lot of pre-existing VM/370 knowledge, or are woefully out of date. So here are just a couple of notes should anyone else be interested in playing around with a fake mainframe…

Some notes about my environment:

• Dual-core AMD Athlon64 2GHz
• 1 GB RAM (yes, I know, it needs more memory)
• Ubuntu 10.04 LTS, aka Lucid

Ubuntu Lucid has a good binary version of Hercules in the repositories. So no compilation is required, at least not for any of the basic features that I was initially interested in. A quick apt-get hercules and apt-get x3270 were the only necessities.

In general, I followed the instructions at gunkies.org: Installing VM/370 on Hercules. However, there were a few differences. The guide is geared towards someone running Hercules on Windows, not Linux.

• You do not need to set everything up in the same location as the Hercules binaries, as the guide seems to indicate. I created a vm370 directory in my user home, and it worked fine as a place to set up the various archives and DASD files (virtual machine drives).

• The guide takes you through sequences where you boot the emulated machine, load a ‘tape’, reboot, then load the other ‘tape’. When I did this, the second load didn’t work (indefinite hang until I quit the virtual system from the Hercules console). But after examining the DASD files, it seemed like the second tape had loaded anyway, but the timestamp indicated that it had loaded at the same time as the first tape. I think that they both loaded one after the other in the first boot cycle -- hard to tell for sure at this point, but don't be too concerned if things don't seem to work as described; I got a working system anyway. Update: The instructions work as described; I had a badly set-up DASD file that was causing an error, which did not show itself until later when I logged in and tried to start CMS.

• To get a 3270 connection, I had to connect to 127.0.0.1 on port 3270; trying to connect to “localhost” didn’t work. I assume this is just a result of how Hercules is set up to listen, but it caused me to waste some time.

• The tutorial tells you to start Hercules, then connect your 3270 emulator to the virtual system, then run the ipl command; the expected result is to see the loader on the 3270. For me, this didn’t work… the 3270 display just hung at the Hercules splash screen. To interact with the loader, I had to disconnect and reconnect the 3270 emulator. So, rather than starting Hercules, connecting the 3270, then ipl-ing, it seems easier to start Hercules, ipl, then connect and operate the loader.

Of course, when you get through the whole procedure, what you’ll have is a bare installation of VM/370… without documentation (or extensive previous experience), you can’t do a whole lot. That’s what I’m figuring out now. Perhaps it’ll be the subject of a future entry.

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