PiDP-8/I Software

How to Run a Naked PiDP-8/I
Log In

The Situation

"The S in IoT stands for Security."

The PiDP-8/I binary OS images shipped from this site are fairly well locked down. They ship with the normal Raspbian default user name changed to an uncommon name, that user has a very strong default password which you are forced to change on first login to something different, the OS won't accept a weak password by default, and there are no networked services running.

(OpenSSH must be manually reawakened after installation, and, once done, the default configuration on Raspbian is quite secure.)

Yet, some people want their PiDP-8/I to just be an appliance: they want it to turn on and run the PDP-8 simulator: no user names, no passwords. I resist shipping OS images configured this way because Raspbian is a full-featured operating system. When networked, it is capable of being a powerful island for an attacker on the network. Even some of the most heavily-protected web services have been taken down by small armies of lesser systems — such as networked printers — pounding on them in concert.

I refuse to build OS images that contribute to this problem.

I also do not believe in restricting access to technical information, even when making use of that information is highly inadvisable, so in that spirit, I will shortly describe how to discard the provided security provisions.

Before I get to that, you may want to consider using the serial or Telnet console options instead. Those methods have fewer security problems, yet achieve much the same end.

Getting Rid of the Login Prompt

The first thing you have to do on logging in is change your user name back from pidp8i to pi, because some changes we will make below only work properly with user pi due to hard-coded configuration files in the stock OS.

Give these commands, being very careful how you type them, because you can lock yourself out of the system if you fat-finger them:

$ exec sudo -i
# systemctl stop pidp8i
# killall -u pidp8i -9
# usermod -l pi -d /home/pi -m pidp8i
# groupmod -n pi pidp8i
# exit

Now log back in as user pi, with the same password you had for user pidp8i prior to this change.

If you have the PiDP-8/I PCB attached to your Pi and you try to restart the simulator, the front panel will not light up now. This is because the PiDP-8/I software was built with the knowledge that the default user name was pidp8i. You need to rebuild and reinstall it to fix this:

$ cd ~/pidp8i
$ rm .fslckout
$ fossil user default pidp8i
$ fossil open ~/museum/pidp8i.fossil release
$ ./configure && tools/mmake && sudo make install
$ sudo systemctl restart pidp8i

That should light the panel back up.

Now we can finally set up auto-login:

$ sudo raspi-config

Then go to Boot OptionsDesktop / CLIConsole Autologin.

It will offer to reboot your system to test this. It should succeed.

Attaching the Console to the Simulator by Default

Instead of booting to a Linux command prompt, you may prefer to have the Raspbian console attached to the PiDP-8/I simulator console, so that you see the program you're simulating: OS/8, TSS/8, Spacewar! or what have you.

The simplest way I can think of to do that is:

$ echo pidp8i >> ~/.profile
$ sudo reboot

That should drop you into the SIMH console after the host OS boots.

If you need to get back to Linux, there are a couple of ways.

If you just need to run a single command, you can press Ctrl-E and then run your command from the sim> prompt with the ! shell escape:

sim> !df -h
...disk free space report...
sim> c
...simulation continues...

If you need to do more than that, I recommend quitting out of SIMH via Ctrl-E quit. Do your Linux work, and when done, re-start the simulator and re-attach to it:

$ sudo systemctl restart pidp8i
$ pidp8i


Copyright © 2017-2019 by Warren Young. This document is licensed under the terms of the SIMH license.