2001.10_The Cups Printing System.pdf

COVER FEATURE

PRINTING WITH CUPS

PRINT -O MATIC

The Common UNIX Printing System

ULRICH WOLF

CUPS is the printing system of the Internet era.

Our overview shows what can now be done with

it, and what’s going on behind the scenes.

CUPS implements the Internet Printing Protocol

(IPP) in Version 1.1. It can completely supersede,

both locally as well as on the network, the ageing

Line Printer Daemon. A few Linux distributions such

as Mandrake, Caldera, EasyLinux or Connectiva

have already stopped installing the LPD. And in the

latest SuSE variants CUPS can now be configured

with YaST.

On stand-alone workstations CUPS exhausts all

the individual properties of the existing printer, but

its real strengths only come into play on the

network. This is where, on any free printer, it is

possible to print using all its usual device options,

without a driver having been installed on the client.

More than that, the client automatically recognises

which printers are installed in the network, provided

these are attached to a CUPS server.

Architecture like a webserver

The beating heart of CUPS is the server daemon or

scheduler cupsd , which is similar to an ordinary

webserver. It can be addressed with any browser via

the reserved port 631. Clients also communicate

with the server via this port. But the exchange of

data with the printers connected to the server can

occur in a variety of ways. Ideally these can even

cope with IPP, but this is only the case in some 200

models. Good laser printers such as the ones in our

test are more likely to be able to use the Appsocket

protocol, free printers on Windows computers can

be addressed with Samba via SMB. For the rest LPD

is used. Communication with the printers via these

protocols is done by back-ends, which are

separately configured.

Gimp Print for inkjet printers, a

universal driver with special abilities

CUPS and Postscript

Anyone printing on UNIX systems cannot avoid

Postscript; CUPS is no exception to this rule. So the

simplest way is to use Postscript-compatible

printers. Their integrated processors process PS

files into raster data in the highly calculation-

intensive Raster Image Process (RIP). For printers

which cannot cope with Postscript, a computer

has to do it.

There are often dedicated RIP servers in the

preliminary print stage. In a company network, were

there are printers which are not Postscript-

compatible being used regularly, the print server

takes over these tasks and should therefore have

sufficient computing power. CUPS is flexible

enough to allow the preparation of print data on

the client. But then the client obviously needs its

own driver. The characteristics of each printer model

are defined in a Postscript Printer Description (PPD)

in ASCII format.

About 120 inkjet printers from the companies Epson, HP, Canon and Lexmark are

supported by the latest Alpha version (4.1.99-a2) of the Gimp Print Project (last

stable version is the 4.0.5).

Gimp Print includes a joint code base for three different target projects: GIMP,

Ghostscript and CUPS.

./configure - -help displays the options. The CUPS system can be expanded using

- -with-cups . The option - -with-ghost - -with-foomatic generates the source

code files which are merged with the Ghostscript source code. Then Ghostscript is

recompiled. As a new component it now includes stp . The CUPS/Gimp Print filter

together with the PPDs created and the normal Ghostscript filter, here under the

name stp , can be used with CUPS.

The following points are important to remember:

The PPDs must match the filter: the foomatic files belong to stp as can be seen as

GIMPPRINT+foomatic or stp+foomatic

The CUPS form of Gimp Print is called CUPS + gimp-print

Only copy PPDs from other computers with the appropriate conversion filter

Avoid Gimp Print, Foomatic or stp and associated PPDs in PostScript printers

24 LINUX MAGAZINE 13 · 2001

PRINTING WITH CUPS

COVER FEATURE

Printing without Postscript

devices

Info

CUPS homepage

http://www.cups.org

CUPS filters, are based on the older Ghostscript

version 5.5, but have been modified and improved.

Some filters are in place after the standard

installation: for PCL-compatible inkjet and laser

printers from the Deskjet and Laserjet families of

Hewlett-Packard, Epson Stylus Color and Stylus

Photo and 9-pin and 24-pin printers from Epson.

These are usually found, together with the filters

derived from Ghostscript, in the directory

/usr/lib/cups/filter .

For other, non-Postscript-compatible printers

there is Cups-O-Matic. This is a version of the

Foomatic script collection adapted to CUPS by the

Linux Printing HOWTO author Grant Taylor. It covers

all Ghostscript filters for use with the CUPS system

and thus requires that Ghostscript is installed on the

print server. On the Cups-O-Matic website, you first

create a PPD for the existing printers in combination

with a Ghostscript filter. From the point of view of

the user, this is already the printer driver and can be

installed in the CUPS system by the usual methods

(command line, GUI or browser). Internally,

however, you will need cupsomatic , a Perl script

which must sit in the filter directory

/usr/lib/cups/filter . With the aid of this script the

printer-specific data from the PPD is sent to the

relevant Ghostscript filter of the system, which then

prepares the print data accordingly.

IPP specification

http://www.ietf.org/html.charters/ipp

-charter.html

Linux printing homepage/Cups-O-Matic

http://www.linuxprinting.org

Gimp Print

http://gimp-print.sourceforge.net/

CUPS documentation

http://www.cups.org/documentation.html

The graphical front-end Xpp is heavily based on the ESP

PrintPro software of the inventor of CUPS, Michael Sweet

rights. CUPS has its own administrator, so needs no

root rights. With lpoptions all the printer

characteristics, which can be configured via the

PPD, can be displayed and altered. But this is very

tedious, since they vary from model to model. This is

why in this case graphical tools like xpp , gtklp, kups ,

or the Web interface via http://[computername]:631

are vital. These read out the respective PPDs and

make them configurable with a mouse.

In KDE 2.2, KDEPrint is an intermediate layer

between KDE applications and various printing

subsystems. This means CUPS can be

administered more simply in KDE applications.

The former configuration tool kups is no longer

being developed.

General settings for the CUPS print system can be

found in /etc/cups/cupsd.conf . This is similar to the

Apache configuration file httpd.conf . In cupsd.conf

it is possible to announce printers to the whole

network, using Browsing On , define browse relays

for inter-network printing, options for

authentication and encryption and much more.

CUPS is largely ready to use with the default

settings as soon as it has been installed.

CUPS and Ghostscript

Cupsomatic passes the print data out of the usual

CUPS environment to the Ghostscript filter specified

in the Cups-O-Matic-PPD and returns the result to

CUPS. With Cups-O-Matic, then, CUPS prints as

good as any other Ghostscript systems, but all

network features of CUPS for the printers

supported by Ghostscript are available.

Apart from Cups-O-Matic there are other options

for integrating filters in CUPS, namely for Turboprint

and Gimp-Print.

Big print runs

If there are several printers of the same type in a

network, or if certain printers are only available for

a short time, these can be combined into classes. If

a print job is sent to a class, the job goes to the

next free device. In this way, it is possible to achieve

load balancing.

Configuration of CUPS

The CUPS print system can be monitored and

administered via diverse command line commands.

The main ones are lpadmin , lpoptions and lpstat .

With lpstat -p -d the available printers are displayed.

lpadmin configured printers, printer classes and user

In KDE 2.2 the CUPS configuration is integrated

seamlessly, thanks to KDEPrint, into the system control

13 · 2001 LINUX MAGAZINE 25

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