[Simh] Unattended background SIMH process

[Seth J. Morabito]

Has anyone got a clean solution for running a background SIMH process
that doesn't involve `screen` or `tmux`?

I would like to create an init script or systemd module that will kick
off a simulator as a daemon process that can start up on host boot, and
shut down on host shutdown. I've made some progress toward this goal on
FreeBSD, but the startup script I've come up with
[/usr/local/etc/rc.d/simh] does involve using `tmux` to wrap the
process, and it's not exactly clean. If anyone is interested in reading
the rc script, I've shared it here:
https://archives.loomcom.com/share/simh-rc-script

My 3B2 simulator init script then has the following block:

    ...
    SET ON
    ON SIGTERM SET TIMER SHUTDOWN ; CONTINUE
    ON STOP EXIT

(The 'SET TIMER SHUTDOWN' command tells the simulator to initiate a
software shutdown in the same way a real 3B2 shuts itself down after the
soft power switch is toggled. Other architectures will have other
needs...)

It mostly works, but not always, and I haven't been able to do a deep
dive to understand why.

I guess my ideal way to do this all would be to have a daemonizable SIMH
that can use a buffered telnet console that does not need any operator
intervention to boot, run, and shut down cleanly. I have experimented
with the telnet console, but it seems that it always requires an active
telnet connection to run, and will kill the simulator when the telnet
connection is severed (unless this is operator error on my part).

So, if anyone has any ideas, I would love to hear them. Has anyone else
worked on this?

-Seth
--
Seth Morabito
Poulsbo, WA, USA
web at loomcom.com