Experimental Physics and
Industrial Control System

"Brian McAllister" <[email protected]> · Wed, 09 Nov 2005 14:35:36 -0500

  > Can somebody explain this behavior?  Something about process groups or
  > controlling terminal requiring a shell process to go between the
  > 'screen' and the soft IOC?

You don't need a shell, just a terminal.  Screen really wants to be
associated with a terminal, for obvious reasons.  The exception to this is
when it is running "detached".

So, the key is to *always* start screen detached [-d -m].  You can then
"re-attach" at any time by using "screen -r" (as the user owning the screen
process).  Output from the IOC will be buffered by screen while detached
(up to a user-definable number of lines) and can be reviewed later [see
"scrollback buffer"].  When done, you detach it again [C-a C-d].

This approach works both from startup scripts and from the command line, so
you can use the same "boot" script for both.

Here's our init.d script [RedHat 7.3].  It assumes you don't have any other
"screen" processes running:

================

#!/bin/bash
# init file for EPICS Linux IOC

# Source networking configuration.
. /etc/sysconfig/network

# Check that networking is up.
[ ${NETWORKING} = "no" ] && exit 0

# source function library
. /etc/init.d/functions

RETVAL=0
prog="epicsIoc"
host=$(hostname -s)

start() {
	echo -n $"Starting $prog: "
        daemon --user epics /home/locus/epics/IOC_runtime/${host}App/current/BOOT_ioc${host}
	RETVAL=$?
	echo
	touch /var/lock/subsys/epicsIoc
	return $RETVAL
}

stop() {
	echo -n $"Stopping $prog: "
	killproc SCREEN
	RETVAL=$?
	echo
	rm -f /var/lock/subsys/epicsIoc
	return $RETVAL
}

case "$1" in
  start)
	start
	;;
  stop)
	stop
	;;
  restart)
	stop
	start
        ;;
  status)
        status SCREEN
	RETVAL=$?
        ;;
  *)
	echo $"Usage: $0 {start|stop|status|restart}"
	RETVAL=1
esac

exit $RETVAL

==================

The IOC script is just this:

==================

#!/bin/bash

cd {IOC directory}

screen -d -m iocXXXX XXXX.cmd 

----
Brian McAllister                                   Senior Software Engineer
[email protected]                             MIT-Bates Linear Accelerator
(617) 253-9537                                                Middleton, MA

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System