A number of CUPS features have been adapted for SUSE Linux. Some of the most important changes are covered here.
There are several ways to configure CUPS as the client of a network server.
For every queue on the network server, you can configure a local queue through which to forward all jobs to the corresponding network server (forwarding queue). Usually, this approach is not recommended, because all client machines must be reconfigured whenever the configuration of the network server changes.
Print jobs can also be forwarded directly to one network server. For this type of configuration, do not run a local CUPS daemon. lp or corresponding library calls of other programs can send jobs directly to the network server. However, this configuration does not work if you also want to print on a local printer.
The CUPS daemon can listen to IPP broadcast packets that other network servers send to announce available queues.
This is the best CUPS configuration for printing over remote CUPS servers. However, there is a risk that an attacker sends IPP broadcasts with queues and the local daemon accesses a counterfeit queue. If it then displays the queue with the same name as another queue on the local server, the owner of the job may believe the job is sent to a local server, while in reality it is sent to the attacker's server.
YaST can find CUPS servers by either scanning local network hosts to see if they offer the IPP service or by listening to IPP broadcasts. This requires the firewall to let incoming packets on port 631/UDP (service IPP client) pass through. This is automatically enabled when you have configured your machine to be in the internal firewall zone. Opening a port to configure access to remote queues in the external zone can be a security risk because an attacker could broadcast a server that might be accepted by users. By default IPP broadcasts are rejected in the external zone. See Section 18.104.22.168, “Configuring with YaST” for details on firewall configuration.
Alternatively, the user can detect CUPS servers by actively scanning the local network hosts or configure all queues manually. However, because of the reasons mentioned in the beginning of this section, this method is not recommended.
These changes were initially applied for SUSE Linux 9.1.
On start-up, cupsd changes from the user
root to the user
lp. This provides a much higher level of
security, because the CUPS print service does not run with unrestricted
permissions, only with the permissions needed for the print service.
However, the authentication (the password check) cannot be performed
lp has no access to
/etc/shadow. Instead, the CUPS-specific
/etc/cups/passwd.md5 must be
used. For this purpose, a CUPS administrator with the CUPS administration
sys and a CUPS password
must be entered in
/etc/cups/passwd.md5. To do this,
enter the following as
lppasswd -g sys -a CUPS-admin-name
This setting is also essential if you want to use the CUPS administration Web front-end or the KDE printer administration tool.
When cupsd runs as
cannot be generated, because
is not permitted to create files in
Therefore, cupsd generates
/etc/cups/printcap. To ensure that applications that
can only read queue names from
to work properly,
/etc/printcap is a symbolic link
When cupsd runs as
631 cannot be
opened. Therefore, cupsd cannot be reloaded with
rccups reload. Use rccups restart
The access permissions set for
BrowseDeny apply to all kinds of packages sent to
cupsd. The default settings in
/etc/cups/cupsd.conf are as follows:
BrowseAllow @LOCAL BrowseDeny All
<Location /> Order Deny,Allow Deny From All Allow From 127.0.0.1 Allow From 127.0.0.2 Allow From @LOCAL </Location>
In this way, only
LOCAL hosts can access
cupsd on a CUPS server.
are hosts whose IP addresses belong to a non-PPP interface (interfaces
IFF_POINTOPOINT flags are not set) and whose IP
addresses belong to the same network as the CUPS server. Packets from all
other hosts are rejected immediately.
In a standard installation, cupsd is activated
automatically, enabling comfortable access to the queues of CUPS network
servers without any additional manual actions. The items in
Section 22.214.171.124, “cupsd Runs as the User lp” and Section 126.96.36.199, “Generalized Functionality for
BrowseDeny” are vital preconditions for this
feature, because otherwise the security would not be sufficient for an
automatic activation of cupsd.
The YaST printer configuration sets up the queues for CUPS using only
the PPD files installed in
the system. To find the suitable PPD files for the printer model, YaST
compares the vendor and model determined during hardware detection with
the vendors and models in all PPD files available in
/usr/share/cups/model/ on the system. For this
purpose, the YaST printer configuration generates a database from the
vendor and model information extracted from the PPD files. When you
select a printer from the list of vendors and models, receive the PPD
files matching the vendor and model.
The configuration using only PPD files and no other information sources
has the advantage that the PPD files in
/usr/share/cups/model/ can be modified freely. The
YaST printer configuration recognizes changes and regenerates the vendor
and model database. For example, if you only have PostScript printers,
normally you do not need the Foomatic PPD files in the
cups-drivers package or the Gimp-Print PPD files
cups-drivers-stp package. Instead, the PPD
files for your PostScript printers can be copied directly to
/usr/share/cups/model/ (if they do not already exist
manufacturer-PPDs package) to achieve an
optimum configuration for your printers.
The generic PPD files in the
cups package have
been complemented with adapted Foomatic PPD files for PostScript level 1
and level 2 printers:
Normally, the Foomatic printer filter
foomatic-rip is used together with Ghostscript
for non-PostScript printers. Suitable Foomatic PPD files have the entries
*NickName: ... Foomatic/Ghostscript driver and
*cupsFilter: ... foomatic-rip. These PPD files
are located in the
YaST prefers a Foomatic PPD file if a Foomatic
PPD file with the entry
*NickName: ... Foomatic ...
(recommended) matches the printer model and the
manufacturer-PPDs package does not contain a
more suitable PPD file.
foomatic-rip, the CUPS filter
rastertoprinter from Gimp-Print can be used for
many non-PostScript printers. This filter and suitable Gimp-Print PPD
files are available in the
package. The Gimp-Print PPD files are located in
/usr/share/cups/model/stp/ and have the entries
*NickName: ... CUPS+Gimp-Print and
*cupsFilter: ... rastertoprinter.
manufacturer-PPDs package contains PPD files
from printer manufacturers that are released under a sufficiently liberal
license. PostScript printers should be configured with the suitable PPD
file of the printer manufacturer, because this file enables the use of all
functions of the PostScript printer. YaST prefers a PPD file from the
manufacturer-PPDs package if the following
conditions are met:
The vendor and model determined during the hardware detection
match the vendor and model in a PPD file from the
The PPD file from the
package is the only suitable PPD file for the printer model or a there
is a Foomatic PPD file with a
Foomatic/Postscript (recommended) entry that also matches
the printer model.
Accordingly, YaST does not use any PPD file from the
package in the following cases:
The PPD file from the the
package does not match the vendor and model. This may happen if the
manufacturer-PPDs package contains only one
PPD file for similar models, for example, if there is no separate PPD
file for the individual models of a model series, but the model name is
specified in a form like
series in the PPD file.
The Foomatic PostScript PPD file is not recommended. This may be because the printer model does not operate efficiently enough in PostScript mode, for example, the printer may be unreliable in this mode because it has too little memory or the printer is too slow because its processor is too weak. Furthermore, the printer may not support PostScript by default, for example, because PostScript support is only available as an optional module.
If a PPD file from the
package is suitable for a PostScript printer, but YaST cannot configure
it for these reasons, select the respective printer model
manually in YaST.