Solved

Cups and /dev/lp0

Posted on 2014-03-28
6
451 Views
Last Modified: 2014-04-04
Goal: to ensure that a print command issued by ImageMagick 'display' (which apparently wants to print to /dev/lp0) is forwarded to the Cups server

Firstly, i don't know if this is necessary (i probably don't know enough about Cups) but i have the following script:

#!/bin/bash

spooling_file=/tmp/img.ps
printer_dev=/dev/lp0

if [ ! -p ${printer_dev} ];then
    sudo mkfifo ${printer_dev}
fi
while [ true ]; do
    cat ${printer_dev} >${spooling_file}
    lp ${spooling_file}
done

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This works ok, but i thought it should properly become an init.d script so i edited /etc/init.d/skeleton to provide:
#! /bin/sh
### BEGIN INIT INFO
# Provides:          skeleton
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Example initscript
# Description:       This file should be used to construct scripts to be
#                    placed in /etc/init.d.
### END INIT INFO

# Author: Foo Bar <foobar@baz.org>
#
# Please remove the "Author" lines above and replace them
# with your own name if you copy and modify this script.

# Do NOT "set -e"

# PATH should only include /usr/* if it runs after the mountnfs.sh script
PATH=/sbin:/usr/sbin:/bin:/usr/bin
DESC="Use /dev/lp0 with Cups"
NAME=img-backend
DAEMON=/usr/local/bin/$NAME
DAEMON_ARGS="--options args"
PIDFILE=/var/run/$NAME.pid
SCRIPTNAME=/etc/init.d/$NAME

# Exit if the package is not installed
[ -x "$DAEMON" ] || exit 0

# Read configuration variable file if it is present
[ -r /etc/default/$NAME ] && . /etc/default/$NAME

# Load the VERBOSE setting and other rcS variables
. /lib/init/vars.sh

# Define LSB log_* functions.
# Depend on lsb-base (>= 3.2-14) to ensure that this file is present
# and status_of_proc is working.
. /lib/lsb/init-functions

#
# Function that starts the daemon/service
#
do_start()
{
	# Return
	#   0 if daemon has been started
	#   1 if daemon was already running
	#   2 if daemon could not be started
	# start-stop-daemon --start --quiet --background --pidfile $PIDFILE --exec $DAEMON --test > /dev/null \ || return 1
	start-stop-daemon --start --quiet --background --pidfile $PIDFILE --exec $DAEMON -- \
		$DAEMON_ARGS \
		|| return 2
	# Add code here, if necessary, that waits for the process to be ready
	# to handle requests from services started subsequently which depend
	# on this one.  As a last resort, sleep for some time.
}

#
# Function that stops the daemon/service
#
do_stop()
{
	# Return
	#   0 if daemon has been stopped
	#   1 if daemon was already stopped
	#   2 if daemon could not be stopped
	#   other if a failure occurred
	start-stop-daemon --stop --quiet --retry=TERM/30/KILL/5 --pidfile $PIDFILE --name $NAME
	RETVAL="$?"
	[ "$RETVAL" = 2 ] && return 2
	# Wait for children to finish too if this is a daemon that forks
	# and if the daemon is only ever run from this initscript.
	# If the above conditions are not satisfied then add some other code
	# that waits for the process to drop all resources that could be
	# needed by services started subsequently.  A last resort is to
	# sleep for some time.
	start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec $DAEMON
	[ "$?" = 2 ] && return 2
	# Many daemons don't delete their pidfiles when they exit.
	rm -f $PIDFILE
	return "$RETVAL"
}

#
# Function that sends a SIGHUP to the daemon/service
#
do_reload() {
	#
	# If the daemon can reload its configuration without
	# restarting (for example, when it is sent a SIGHUP),
	# then implement that here.
	#
	start-stop-daemon --stop --signal 1 --quiet --pidfile $PIDFILE --name $NAME
	return 0
}

case "$1" in
  start)
	[ "$VERBOSE" != no ] && log_daemon_msg "Starting $DESC" "$NAME"
	do_start
	case "$?" in
		0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
		2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
	esac
	;;
  stop)
	[ "$VERBOSE" != no ] && log_daemon_msg "Stopping $DESC" "$NAME"
	do_stop
	case "$?" in
		0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
		2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
	esac
	;;
  status)
	status_of_proc "$DAEMON" "$NAME" && exit 0 || exit $?
	;;
  #reload|force-reload)
	#
	# If do_reload() is not implemented then leave this commented out
	# and leave 'force-reload' as an alias for 'restart'.
	#
	#log_daemon_msg "Reloading $DESC" "$NAME"
	#do_reload
	#log_end_msg $?
	#;;
  restart|force-reload)
	#
	# If the "reload" option is implemented then remove the
	# 'force-reload' alias
	#
	log_daemon_msg "Restarting $DESC" "$NAME"
	do_stop
	case "$?" in
	  0|1)
		do_start
		case "$?" in
			0) log_end_msg 0 ;;
			1) log_end_msg 1 ;; # Old process is still running
			*) log_end_msg 1 ;; # Failed to start
		esac
		;;
	  *)
		# Failed to stop
		log_end_msg 1
		;;
	esac
	;;
  *)
	#echo "Usage: $SCRIPTNAME {start|stop|restart|reload|force-reload}" >&2
	echo "Usage: $SCRIPTNAME {start|stop|status|restart|force-reload}" >&2
	exit 3
	;;
esac

:

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Incidentally do_start was originally

do_start()
{
	# Return
	#   0 if daemon has been started
	#   1 if daemon was already running
	#   2 if daemon could not be started
	start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test > /dev/null \
		|| return 1
	start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON -- \
		$DAEMON_ARGS \
		|| return 2
	# Add code here, if necessary, that waits for the process to be ready
	# to handle requests from services started subsequently which depend
	# on this one.  As a last resort, sleep for some time.
}

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but i deleted the --test business, firstly because i didn't know what was going on and secondly because with it in, it simply caused two processes to get run.

Starting went off ok, but (possibly because of the infinite loop [i don't know]) no pid file ever got created so stopping the 'service' simply failed.

So the question is

a. is my workaround even necessary?
b. if yes, how can i ensure proper working of the script as far as changing state is concerned (between running, stopped, status etc)
0
Comment
Question by:CEHJ
  • 4
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6 Comments
 
LVL 40

Assisted Solution

by:noci
noci earned 265 total points
ID: 39964422
isn't it easier to convert an image to PostScript and then print it?
like:

convert file.gif ps:- | lp -P queue

(which converts file.gif  to ps on stdout...)
Another option can be ( need to read up cups for this), to specify an input format filter
that recognizes the .gif  etc. etc. and converts it to ps on the fly.
0
 
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Author Comment

by:CEHJ
ID: 39964631
The application from which i'm printing already prints to that device file in Postscript format
0
 
LVL 40

Expert Comment

by:noci
ID: 39964745
yes but separating jobs that come through a pipe is a pain to do.
So in stead of using display to print an image use the other ImageMagick command convert to transpose it to PS and feed that to the cups queue... A lot less hassle.

And if you have to process a lot of file you could make a directory,
run incron on it and every time you drop a file into that directory the incron job can process the file.
0
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LVL 86

Accepted Solution

by:
CEHJ earned 0 total points
ID: 39964768
Perhaps i didn't make this sufficiently clear, but the whole purpose is to be able (for someone who is not a 'power user') to use the Print menu item in the display program.

I'm actually fairly happy with the above, apart from the aforementioned problem of the lack of pid file and therefore the inability to stop the daemon. Perhaps it's to do with the script blocking on IO?
0
 
LVL 86

Author Comment

by:CEHJ
ID: 39964810
Actually i think the pid file issue is simply solved by specifying --make-pidfile to start-stop-daemon. I assumed (incorrectly) that start-stop-daemon created this
0
 
LVL 86

Author Closing Comment

by:CEHJ
ID: 39977627
Thanks. Issue solved by --make-pidfile
0

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