Un problema bastante desconcertante que
me ocurría a veces es que las impresoras conectadas por USB me aparecían
dos veces en la lista de impresoras y en /etc/cups/printers.conf, como
si CUPS pensase que eran impresoras distintas, aun cuando su DeviceURI
era igual. Este problema se hacía mas frecuente cuando cambiaba el
nombre de la impresora y ponía uno a mi gusto, en lugar de el que le
había dado CUPS en la autodetección, o cuando usaba el filtro
tea4cups para controlar los trabajos enviados a las cola de impresión.
Como
utilizo tea4cups para llevar una contabilidad de las páginas impresas,
el que las impresoras apareciesen duplicadas me originaba un problema a
la hora de recopilar los datos, además de desconcertar al usuario a la
hora de imprimir.
Mi
compañero Ubaldo me puso en la pista de como resolver el problema. En
el paquete system-config-printer-udev están los scripts encargados de
manejar las impresoras USB detectadas por udev. En concreto el script
/lib/udev/udev-add-printer es el que se encarga de añadir a CUPS una
nueva impresora cuando es detectada por primera vez. Estaba claro que
algo fallaba ahí y que había que retocar el código del script para
evitar que se duplicase. Afortunadamente el script estaba en python.
El script retocado queda así (pongo en rojo las líneas añadidas por mí):
#!/usr/bin/python
## udev-add-printer
## Copyright (C) 2009, 2010 Red Hat, Inc.
## Author: Tim Waugh <twaugh@redhat.com>
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
import cups
import cupshelpers
import dbus
import os
import sys
import traceback
from syslog import *
MFG_BLACKLIST=[
"graphtec",
]
def create_queue (c, printers, name, device_uri, ppdname, info, installer):
# Make sure the name is unique.
namel = unicode (name.lower ())
unique = False
suffix = 1
while not unique:
unique = True
for printer in printers.values ():
if (not printer.discovered and
((suffix == 1 and printer.name.lower () == namel) or
(suffix > 1 and
printer.name.lower () == namel + "-" + str (suffix)))):
unique = False
break
if not unique:
suffix += 1
if suffix == 100:
break
if suffix > 1:
name += "-" + str (suffix)
c.addPrinter (name,
device=device_uri,
ppdname=ppdname,
info=info,
location=os.uname ()[1])
if not installer:
# There is no session applet running to deal with installing
# drivers so there is a good chance that this queue won't work
# right now. If that's the case, delete it. The user can
# reconnect the printer when they log in, and everything will
# be set up correctly for them at that point.
try:
ppdfile = c.getPPD (name)
ppd = cups.PPD (ppdfile)
os.unlink (ppdfile)
(pkgs, exes) = cupshelpers.missingPackagesAndExecutables (ppd)
if pkgs or exes:
# There are filters missing. Delete the queue.
syslog (LOG_ERROR, "PPD %s requires %s" % (ppdname,
repr ((pkgs, exes))))
syslog (LOG_ERROR, "Deleting non-functional queue")
c.deletePrinter (name)
name = None
except cups.IPPError, (e, m):
pass
except RuntimeError:
pass
if name:
cupshelpers.activateNewPrinter (c, name)
return name
def add_queue (device_id, device_uris, fax_basename=False):
"""
Create a CUPS queue.
device_id: the IEEE 1284 Device ID of the device to add a queue for.
device_uris: device URIs, best first, for this device
fax_basename: False if this is not a fax queue, else name prefix
"""
id_dict = cupshelpers.parseDeviceID (device_id)
if id_dict["MFG"].lower () in MFG_BLACKLIST:
syslog (LOG_DEBUG, "Ignoring blacklisted manufacturer %s", id_dict["MFG"])
return
syslog (LOG_DEBUG, "add_queue: URIs=%s" % device_uris)
installer = None
if fax_basename != False:
notification = None
else:
try:
bus = dbus.SystemBus ()
obj = bus.get_object ("com.redhat.NewPrinterNotification",
"/com/redhat/NewPrinterNotification")
notification = dbus.Interface (obj,
"com.redhat.NewPrinterNotification")
notification.GetReady ()
except dbus.DBusException, e:
syslog (LOG_DEBUG, "D-Bus method call failed: %s" % e)
notification = None
try:
obj = bus.get_object ("com.redhat.PrinterDriversInstaller",
"/com/redhat/PrinterDriversInstaller")
installer = dbus.Interface (obj,
"com.redhat.PrinterDriversInstaller")
except dbus.DBusException, e:
syslog (LOG_DEBUG, "Failed to get D-Bus object for "
"PrinterDriversInstaller: %s" % e)
id_dict = cupshelpers.parseDeviceID (device_id)
if installer:
cmd = id_dict["CMD"]
if cmd:
cmd = reduce (lambda x, y: x + ',' + y, cmd)
else:
cmd = ""
try:
installer.InstallDrivers (id_dict["MFG"], id_dict["MDL"], cmd,
timeout=3600)
except dbus.DBusException, e:
syslog (LOG_DEBUG, "Failed to install drivers: %s" % repr (e))
c = cups.Connection ()
ppds = cupshelpers.ppds.PPDs (c.getPPDs ())
(status, ppdname) = ppds.getPPDNameFromDeviceID (id_dict["MFG"],
id_dict["MDL"],
id_dict["DES"],
id_dict["CMD"],
device_uris[0])
syslog (LOG_DEBUG, "PPD: %s; Status: %d" % (ppdname, status))
if status == 0:
# Think of a name for it.
name = id_dict["MDL"]
name = name.replace (" ", "-")
name = name.replace ("/", "-")
name = name.replace ("#", "-")
if fax_basename != False:
name = fax_basename + "-" + name
printers = cupshelpers.getPrinters (c)
#Comprobamos si ya existe un dispositivo con esa URI igual
#o precedida por tea4cups
uri=device_uris[0].lower()
ya_existe=False
for printer in printers.values ():
device_uri=printer.device_uri.lower()
if device_uri == "tea4cups://" + uri or device_uri == uri :
ya_existe=True
break
if ya_existe:
syslog (LOG_DEBUG, "Alta abortada, URI Repetido: %s" % device_uri)
return
#Fin de la comprobacion
uniquename = create_queue (c, printers, name, device_uris[0], ppdname,
"%s %s" % (id_dict["MFG"], id_dict["MDL"]),
installer)
if uniquename != None and fax_basename == False:
# Look for a corresponding fax queue. We can only
# identify these by looking for device URIs that are the
# same as this one but with a different scheme. If we
# find one whose scheme ends in "fax", use that as a fax
# queue. Note that the HPLIP backends do follow this
# pattern (hp and hpfax).
used_uris = map (lambda x: x.device_uri, printers.values ())
for uri in device_uris[1:]:
if uri.find (":") == -1:
continue
(scheme, rest) = uri.split (":", 1)
if scheme.endswith ("fax"):
# Now see if the non-scheme parts of the URI match
# any of the URIs we were given.
for each_uri in device_uris:
if each_uri == uri:
continue
(s, device_uri_rest) = each_uri.split (":", 1)
if rest == device_uri_rest:
# This one matches. Check there is not
# already a queue using this URI.
if uri in used_uris:
break
try:
devices = c.getDevices(include_schemes=[scheme])
except TypeError:
# include_schemes requires pycups 1.9.46
devices = c.getDevices ()
device_dict = devices.get (uri)
if device_dict == None:
break
add_queue (device_dict.get ("device-id", ""),
[uri], fax_basename=uniquename)
else:
# Not an exact match.
uniquename = device_uris[0]
if uniquename != None and notification:
try:
cmd = id_dict["CMD"]
if cmd:
cmd = reduce (lambda x, y: x + ',' + y, cmd)
else:
cmd = ""
notification.NewPrinter (status, uniquename, id_dict["MFG"],
id_dict["MDL"], id_dict["DES"], cmd)
except dbus.DBusException, e:
syslog (LOG_DEBUG, "D-Bus method call failed: %s" % e)
if len (sys.argv) < 3:
print "Syntax: %s {Device ID} {Device URI} [other device URIs...]"
sys.exit (1)
openlog ("udev-add-printer", 0, LOG_LPR)
try:
add_queue (sys.argv[1], sys.argv[2:])
except SystemExit, e:
sys.exit (e)
except:
(type, value, tb) = sys.exc_info ()
tblast = traceback.extract_tb (tb, limit=None)
if len (tblast):
tblast = tblast[:len (tblast) - 1]
for line in traceback.format_tb (tb):
syslog (LOG_ERR, line.strip ())
extxt = traceback.format_exception_only (type, value)
syslog (LOG_ERR, extxt[0].strip ())
Básicamente lo que hago es comprobar que el DeviceURI de la impresora no existe ya en la lista de impresoras previas, teniendo en cuenta que puede o no tener el prefijo del filtro "tea4cups://". Con esto estaremos a salvo de esas colas de impresión fantasma y tendremos la cola de impresión ajustada a la realidad.
A otra cosa, mariposa....
