7.4. Network Printers

openSUSE Documentation Chapter 7. Printer Operation / 7.4. Network Printers
	7.3. Installing the Software		7.5. Graphical Printing Interfaces

A network printer can support various protocols, some of them even concurrently. Although most of the supported protocols are standardized, some manufacturers expand (modify) the standard because they test systems that have not implemented the standard correctly or because they want to provide certain functions that are not available in the standard. Manufacturers then provide drivers for only a few operating systems, eliminating difficulties with those systems. Unfortunately, Linux drivers are rarely provided. The current situation is such that you cannot act on the assumption that every protocol works smoothly in Linux. Therefore, you may have to experiment with various options to achieve a functional configuration.

	Remote Access Settings
By default, the cupsd only listens on internal network interfaces (`localhost`). When setting up a CUPS network server you need to adjust the `Listen` directive in `/etc/cups/cupsd.conf` to listen to the outer network.

CUPS supports the socket, LPD, IPP, and smb protocols.

socket: Socket refers to a connection in which the data is sent to an Internet socket without first performing a data handshake. Some of the socket port numbers that are commonly used are 9100 or 35. The device URI (uniform resource identifier) syntax is socket://IP.of.the.printer:port, for example, socket://192.168.2.202:9100/.
LPD (Line Printer Daemon): The proven LPD protocol is described in RFC 1179. Under this protocol, some job-related data, such as the ID of the printer queue, is sent before the actual print data is sent. Therefore, a printer queue must be specified when configuring the LPD protocol for the data transmission. The implementations of diverse printer manufacturers are flexible enough to accept any name as the printer queue. If necessary, the printer manual should indicate what name to use. LPT, LPT1, LP1, or similar names are often used. An LPD queue can also be configured on a different Linux or Unix host in the CUPS system. The port number for an LPD service is 515. An example device URI is lpd://192.168.2.202/LPT1.
IPP (Internet Printing Protocol): IPP is a relatively new (1999) protocol based on the HTTP protocol. With IPP, more job-related data is transmitted than with the other protocols. CUPS uses IPP for internal data transmission. This is the preferred protocol for a forwarding queue between two CUPS servers. The name of the print queue is necessary to configure IPP correctly. The port number for IPP is 631. Example device URIs are ipp://192.168.2.202/ps and ipp://192.168.2.202/printers/ps.
SMB (Windows Share): CUPS also supports printing on printers connected to Windows shares. The protocol used for this purpose is SMB. SMB uses the port numbers 137, 138, and 139. Example device URIs are smb://user:password@workgroup/smb.example.com/printer, smb://user:password@smb.example.com/printer, and smb://smb.example.com/printer.

The protocol supported by the printer must be determined before configuration. If the manufacturer does not provide the needed information, the command nmap, which comes with the nmap package, can be used to guess the protocol. nmap checks a host for open ports. For example:

nmap -p 35,137-139,515,631,9100-10000 printerIP

7.4.1. Configuring CUPS with Command Line Tools

Apart from setting CUPS options with YaST when configuring a network printer, CUPS can be configured with command line tools like lpadmin and lpoptions. You need a device URI consisting of a back-end, such as USB, and parameters, like /dev/usb/lp0. For example, the full URI could be parallel:/dev/lp0 (printer connected to the first parallel port) or usb:/dev/usb/lp0 (first detected printer connected to the USB port).

With lpadmin, the CUPS server administrator can add, remove, or manage class and print queues. To add a print queue, use the following syntax:

lpadmin -p queue -v device-URI -P PPD-file -E

Then the device (-v) is available as queue (-p), using the specified PPD file (-P). This means that you must know the PPD file and the name of the device to configure the printer manually.

Do not use -E as the first option. For all CUPS commands, -E as the first argument sets use of an encrypted connection. To enable the printer, -E must be used as shown in the following example:

lpadmin -p ps -v parallel:/dev/lp0 -P \
/usr/share/cups/model/Postscript.ppd.gz -E

The following example configures a network printer:

lpadmin -p ps -v socket://192.168.2.202:9100/ -P \
/usr/share/cups/model/Postscript-level1.ppd.gz -E

For more options of lpadmin, see the man page of lpadmin(1).

During printer setup, certain options are set as default. These options can be modified for every print job (depending on the print tool used). Changing these default options with YaST is also possible. Using command line tools, set default options as follows:

First, list all options:
```
lpoptions -p queue -l
```
Example:
```
Resolution/Output Resolution: 150dpi *300dpi 600dpi
```
The activated default option is identified by a preceding asterisk (*).
Change the option with lpadmin:
```
lpadmin -p queue -o Resolution=600dpi
```

Check the new setting:

lpoptions -p queue -l

Resolution/Output Resolution: 150dpi 300dpi *600dpi

When a normal user runs lpoptions, the settings are written to ~/.lpoptions. However, root settings are written to /etc/cups/lpoptions.