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.
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