[Simh] Unattended background SIMH process

[Jeremy Begg]

Hi Seth,

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

My solution is pretty clean and doesn't require any kind of virtual TTY.

I have SIMH running under Ubuntu Linux 18.04 on an Intel i3 NUC box.
It took a little trial and error to get it all working (mostly due to
Ubuntu's use of 'netplan' and 'systemd') but it works well enough for me.

It's configured so that my SIMH VAX starts up when Linux starts up.
I don't have it configured to shutdown VAX/VMS or SIMH when Linux is
shutting down, but for my purposes it doesn't need to.  (Or I just haven't
gotten around to it yet; the machine is only rebooted when I want it to.)

Here is my SIMH VAX initialisation script ('eric.ini') between the dashes ...

------------------------------------------------------------------------------
; Set memory to 128M
set cpu 128m
;
: Set CPU emulation characteristics
set cpu idle=vms
set cpu autoboot
set cpu model=MicroVAX
set cpu conhalt
;
; change the 'escape' character from ^E to ^P
set console wru=10
;
; create/load a Non-Volatile RAM file
attach NVR ka655.NVR
;
; disable devices we don't want/need
set LPT disable
set TQ disable
;
; Create and attach two RA80 variant disks
set -l rq0 rauser=4213968
attach rq0 eric_SYSTEM.dsk
set -l rq1 rauser=8427936
attach rq1 eric_USER.dsk
;
; Disable remaining disk devices
set rq2 disable
set rq3 disable
set RL disable
;
; Attach a network interface
attach xq eth0
show xq
;
; Start the VAX console subsystem, show the attached devices and boot VMS
sleep 1s

expect ">>>" send "init\r"; continue
expect ">>>" send "show devices\r"; continue
expect ">>>" send "boot\r"; continue

b cpu
------------------------------------------------------------------------------


SIMH is started at Linux boot by this script ('start_eric.sh') ...

------------------------------------------------------------------------------
#!/bin/sh
#
# start_eric.sh -- invoked by systemd to start ERIC the half-a-VAX at boot
#

whoami
cd /home/eric/

LOGFILE=`date +%Y%m%d-%H%M%S`

simh/vax eric.ini > ${LOGFILE}.log
------------------------------------------------------------------------------

It should be pretty easy to turn start_eric.sh into an INIT script for BSD.

For those who are using a recent Linux like me, here is my systemd script
('/etc/systemd/system/simh-eric.service') ...

------------------------------------------------------------------------------
# /etc/systemd/system/simh-eric.service
# Starts SIMH at system boot to run ERIC the Half-a-VAX
# Created 21-Jul-2019 by Jeremy Begg

[Unit]
Description=ERIC the half-a-VAX
Requires=network-online.target
After=network-online.target

[Service]
User=eric
ExecStart=/home/eric/start_eric.sh
ExecStop=/home/eric/stop_eric.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

------------------------------------------------------------------------------

Once the simulator is running, I can 'tail -f' the log file to watch the VMS
console messages.  However there's no way to enter commands to the VMS console.

I tried using SIMH's "remote console" feature (SIMH listens for incoming
TELNET session on a user-configured TCP port) but found that SIMH stopped
listening if no connection was received within a timeout (not sure how long,
it was only a few minutes at most).

Regards,

        Jeremy Begg

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