11.1 The UNIX Printing Environment
11.1.1 Printing environment components
All network operating systems must provide users with the capability to print to local and remote printers. With the UNIX printing environment, users can have local printers attached to their workstations and can also print to remote network printers. There are three main components in the UNIX printing environment:
  • Printer
  • Printer name (queue)
  • Print server

The system administrator sets up the printing environment by installing printers and defining print queues and servers to support them. The system administrator manages the printing environment. The administrator can control the availability of printers, define default printers, and decide who can print to which printers. They can also manage the print queue for each printer, which is the list of jobs waiting to be printed. Figures and show the major components and protocols for printing within the UNIX environment.

Printer - The printer is a physical printing device. The printer may be attached to a workstation or network server using a parallel cable or in some cases a serial cable as with plotters. Some printers also have an Ethernet or other Network Interface Card (NIC) built in. These can be attached directly to a networking concentration device such as an Ethernet hub or switch. An Ethernet cable such as Category 5 (CAT 5) Unshielded Twisted Pair (UTP) is typically used. Printers can be reserved for use by a particular user or can be centralized to provide access for many users. In the Figure, Local Printer1 and Network Printer3 are attached by parallel cables to computers. Network Printer2 is connected directly to the Ethernet switch via CAT 5 UTP cable as are the computers themselves.

Printer Name (queue) - The printer name is the name of a print queue associated with the physical printer. It is a logical name for the printer, which is assigned by the system administrator. This is the name the users print to. A name such as hplaser1 describes a particular type of printer and this is the first one installed. A name such as acctg1 might be used to refer to the first printer in the accounting department. A printer description can also be included when defining a printer to specify its location or other characteristics. A print queue is a directory on the hard disk of a computer where print requests from users are stored.

Print Server - The print server is the computer that manages incoming print requests and releases them as the printer is ready. Print servers run the printer daemon lpsched, which manages print requests. The print queue is located in the hard disks of the print server. Print requests or print jobs are stored on the hard disk until they are printed and then they are deleted or purged. A print server can be a workstation or a network server. Printers that are attached to a workstation typically use the workstation as the print server and keep the queue with its print requests locally. Printers that are attached to a network server or directly attached to the network typically use a network server as the print server and requests from many different users are processed centrally. Centralized print servers can handle multiple printers and queues.