Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Planning a Workgroup
Planning your Printer Configuration
Chapter 2106
Overview of the LP Spooler
The Line Printer Spooling System (LP spooler) is a set of programs,
shell scripts, and directories that control your printers and the flow of
data going to them.
NOTE Use the LP spooler if your system has more than one user at any given
time. Otherwise, listings sent to the printer while another listing is
printing will be intermixed, thus scrambling both listings.
Even if you have a single-user system, you may want to add your
printer(s) to the LP spooler so you can queue print requests. This way,
you do not have to wait for one request to complete before sending
another.
To understand the LP spooler, think of it as a plumbing system, as shown
in Figure 2-2 on page 107. The data to be printed enters the system like
“water”. Request directories (printer queues) serve as temporary holding
tanks for print requests until they are sent to a printer to be printed. The
request directory and printer control the flow of print requests.
• the terms accept and reject refer to controlling the flow of print
requests to the request directories
• the terms enable and disable refer to controlling the flow of print
requests to the printers
Accepting, rejecting, enabling, and disabling print requests control the
data through the LP spooler as valves would control the flow of water in
a real plumbing system.
Interface scripts (written as shell scripts) near the end of the data flow
serve as pumps which “pump” an orderly flow of data to the printers.
The line printer scheduler (called lpsched) controls the routing of print
requests to the printers. It functions as an automated flow controller in
the “plumbing” system by routing print requests to the physical printers
on a FIFO or priority basis. lpsched enables files to be printed on a
specific printer or printer class. It prevents intermixed listings (that is,
the interspersing of printed pages from different print requests).
lpsched also monitors printer/printout priorities, adjusts printer status,
and logs LP spooler activities.