|
 |
|
| |
7.2. LPD
7.2. LPD
Lpd stands for Line Printer Daemon, and refers in different
contexts to both the daemon and the whole collection of programs
which run print spooling. These are:
-
lpd
-
The spooling daemon. One of these runs to control everything
on a machine, AND one is run per printer while the printer is
printing.
-
lpr
-
The user spooling command. Lpr contacts lpd
and injects a new print job into the spool.
-
lpq
-
Lists the jobs in a print queue.
-
lpc
-
The Lpd system control command. With lpc you can stop, start,
reorder, etc, the print queues.
-
lprm
-
lprm removes a job from the print spool.
So how does it fit together? The following things happen:
-
At boot time, lpd is run. It waits for
connections and manages printer queues.
-
A user submits a job with the lpr command
or, alternatively, with an lpr front-end like GPR, PDQ, etc.Lpr contacts lpd over the
network and submits both the user's data file (containing the
print data) and a control file (containing user options).
-
When the printer becomes available, the main lpd spawns a child lpd to
handle the print job.
-
The child lpd executes the appropriate
filter(s) (as specified in the if attribute in/etc/printcap) for this job and sends the
resulting data on to the printer.
The lp system was originally designed when most printers were line
printers - that is, people mostly printed plain ASCII. By placing
all sorts of magic in the if filter, modern
printing needs can be met with lpd (well, more
or less; many other systems do a better job).
There are many programs useful for writing LPD filters. Among
them are:
-
gs
-
Ghostscript is a host-based Postscript interpreter (aka a
Raster Image Processor or RIP). It accepts Postscript and
produces output in various printer languages or a number of
graphics formats. Ghostscript is covered in Section 10.
-
ppdfilt
-
ppdfilt
is a standalone version of a CUPS
component. It filters Postscript, executing a few basic
transformations on it (n-up printing, multiple copies, etc)
and adding in user option statements according to a Postscript
Printer Definition (PPD) file usually included with Postscript
printers.
ppdfilt is best used together with an
option-accepting LPD system (like the GNUlpr, or LPRng)
and a filter script which parses user-provided options into
the equivalent ppdfilt command. VA Linux
and HP provide a modified rhs-printfilters package which does
exactly this; it produces nice results if you have a
Postscript printer. See Section 8.2.2 for information on
this system.
-
ps2ps
-
ps2ps is a utility script included
with Ghostscript. It filters Postscript into more streamlined
Postscript, possibly at a lower Language Level. This is
useful if you have an older Postscript printer; most modern
software produces modern Postscript.
-
mpage
-
mpage is a utility which accepts
text or Postscript, and generates n-up output—that is,
output with several page images on each piece of paper. There
are actually several programs which do this, includingenscript, nenscript, anda2ps.
-
a2ps
-
a2ps, aka any-to-ps, is a program which
accepts a variety of file types and converts them to
Postscript for printing.
|
|
|
