COHERENT manpages
This page displays the COHERENT manpage for printer [How to attach and run a printer].
List of available manpages
Index
printer -- Technical Information
How to attach and run a printer
A printer is the device that transfers text to paper. The COHERENT system
includes a system for spooling a file to one or more printers. Spooling
means that the file is copied into a special area and printed by a daemon.
With a spooler, more than one user can send files to the same printer at
the same time, yet the files will not collide.
COHERENT also includes commands to prepare text for printing a variety of
printers. These include line printers (that is, dot-matrix printers),
Epson-compatible printers, laser printers that use the PCL page-description
language, and printers that use PostScript. With COHERENT, you can run
prepare text into a variety of formats, and print the output on any number
of printers plugged into either parallel or serial ports.
COHERENT has implemented spooling in two ways. Versions of COHERENT prior
to release 4.2 control printing through a version of the Berkeley command
lpr. COHERENT release 4.2 and subsequent releases also control printing
through the MLP print spooler, which implements a version of the System-V
command lp and related tools. These systems differ greatly; each set is
discussed in its own section below.
Before we begin to describe printing, please note that one major source of
confusion for users is the fact that the same names occur over and over
again. For example, please do not confuse the parallel-port's device
driver lp with the print-spooler command lp or with the device /dev/lp.
COHERENT inherits much of this confusion from the UNIX operating system;
but we will do our best to make these terms clear to you. Caveat lector.
Device Drivers
Both the lpr and lp spoolers work through COHERENT's device drivers for the
serial and parallel ports. The following gives an overview of these
drivers.
The driver lp manages parallel ports. The architecture of the PC permits
your computer to have up to three parallel ports. Devices /dev/lpt1,
/dev/lpt2, and /dev/lpt3 control, respectively, parallel ports 1, 2, and 3
in cooked mode. For more information, see the Lexicon entry for the driver
lp.
COHERENT uses the driver asy to manage all serial ports, whether COM ports
or multi-port cards. For details, see its entry in the Lexicon.
Finding the Port
Both spooler systems require that you be able to identify a port when you
plug a printer into it. This can be more difficult than it seems, largely
because the labels on your system's port may not be reliable: those labels
reflect what MS-DOS thinks the ports are, and that may not be accurate.
The following describes how to identify the port into which you have just
plugged a printer. Note that these directions assume that you are printing
to a parallel port; however, you can adapt them to serial ports as well,
depending on the configuration of serial devices on your system.
1. Plug the printer into an unused port. Load paper into the printer and
turn it on.
2. Log in as the superuser root.
3. cd to directory /dev.
4. Send some output to each parallel port. The output must be something
that your printer can print. If your new printer is a line printer,
type:
cat /etc/uucpname | pr > lpt1
If the printer is a laser printer that uses PCL, type:
cat /etc/uucpname | hp > lpt1
Or, if the printer is a PostScript printer, type:
cat /etc/uucpname | prps > lpt1
If text appears on your printer, then you have discovered the correct
port. Jot down its name on a piece of paper, e.g., ``lpt1''. If
nothing happens, try the command again for lpt2 and lpt3, until you have
found the correct port and noted its name.
5. Exit from superuser status.
The lpr Printing System
Versions of COHERENT prior to release 4.2 use a version of the Berkeley
command lpr to control printing. Although this command can print text onto
printers plugged into either serial or parallel ports, they are almost
always used through parallel ports; therefore, the descriptions in this
section assume that all printers are plugged into parallel ports.
To begin, lpr is actually a family of commands, as follows:
hpd Daemon that prints files on the laser printer
hpr Spool a file for printing on the laser printer
hpskip Abort/restart printing a file on the laser printer
lpd Daemon that prints files on the line printer
lpr Spool a file for printing on the line printer
lpskip Abort/restart printing a file on the line printer
Each command has its own entry in the Lexicon, which describes it in
detail.
The commands lpr and hpr dispatch text to printers: lpr to the printer
plugged into device /dev/lp, and hpr to the printer plugged into device
/dev/hp. Each of these devices is actually a link to the correct parallel
port -- that is, to devices /dev/lpt1, /dev/lpt2, or /dev/lpt3, as
described above. (For information on what a link is, see the Lexicon entry
for the command ln). The fact that each command uses a ``generic'' device
for its output makes it easy for you to dispatch files to the right device;
however, it also means that you can have only one line printer and one
laser printer plugged into your computer.
When you installed COHERENT, the installation program tried to link /dev/lp
and /dev/hp for you automatically; however, you may need to set them
yourself (say, because you have purchased a new printer).
To set these links correctly, first follow the directions given above to
identify the port into which you have plugged the printer. Then, link that
port to the device by which you will access the printer. If you are
installing a line printer that you will access via the command lpr, then
you must use the command ln to link the port to device /dev/lp; if,
however, the printer is a laser printer that you will access via the
command hpr, then you must link the port to device /dev/hp. For example, if
you have plugged a line printer into port lpt1, then use the following
commands:
ln -f lpt1 lp
ln -f rlpt1 rlp
(Please note that the last character in ``lpt1'' and ``rlpt1'' is the
numeral one -- not a lower-case el.) If, however, you have plugged a laser
printer into port lpt3, then use the following commands:
ln -f lpt3 hp
ln -f rlpt3 rhp
After you have made the links, use the command lpr or hpr (whichever is
applicable) to test whether you have set up the links correctly. If you
have not, go through the above procedure again.
The following describes how to use the lpr family of commands to print to a
variety of printers.
Dumb Printers
To print on a line printer, simply use the command lpr. This command
performs some formatting on the file, and invokes the line-printer
daemon lpd to spool the file for printing. For example, to print the
name of your system, use the command:
cat /etc/uucpname | pr | lpr -B
The option -B suppresses the printing of a banner page.
You can also print the output of the text-formatting command nroff on a
line printer, assuming that your line printer understands how to
backspace. For example, the manual pages included with COHERENT were
formatted with nroff. To print the text of this Lexicon entry on your
line printer, type:
man printer | lpr -B
Epson-Compatible Printers
The command epson massages text into a form that uses some of the text-
formatting features of the Epson MX-80 printer and clones thereof. It
is especially to be used with text that has been formatted with nroff:
it turns nroff's character-backspace-character sequence into the Epson
escape sequences for emphasized text and italics. epson writes its
formatted output to the standard output, from which you can pipe it to a
spooler or other program.
For example, to print this manual page on an Epson-compatible printer,
type:
man printer | epson | lpr -B
Laser Printers with PCL
The Hewlett-Packard LaserJet, and its clones, use the Hewlett-Packard
Control Language (HPCL) to control their behavior. Note that some laser
printers, such as the Apple LaserWriter, use PostScript instead of HPCL;
these printers are described below.
The command hp prepares files to be printed on a HPCL printer. (Please
do not confuse this with the device /dev/hp.) You should use it to
prepare simple text, such as program listings, for printing on your
laser printer.
Like the command epson, hp massages the output of nroff into escape
sequences used by a printer -- in this case, escape sequences used by a
printer that's running the Hewlett-Packard Page Control Language (PCL).
For example, to print this manual page on your PCL printer, type:
man printer | hp | hpr -B
The command hpr spools files to be printed on a laser printer. It works
like the command lpr, except that it includes a number of special
features; for example, you can use it to download LaserJet ``soft
fonts'' into your printer.
PostScript Printers
Some laser printers use PostScript instead of HPCL to control their
behavior. These printers expect their input to a program written in the
PostScript language; if you send them ordinary text, they simply hang.
To print ordinary text on a PostScript printer use the command prps,
which is a PostScript version of the COHERENT command pr. It paginates
text, draws a box around the page, and prints a simple header at the top
of each page. For example, to print this manual page on a PostScript
printer, use the command:
man printer | prps | hpr -B
Note that to print on a PostScript printer, you must use the -B option
to the command hpr. If you do not, hpr will attempt to print a banner
page in ordinary text on your printer, and your printer will hang.
The lp Printing System
Versions of COHERENT beginnning with release 4.2 also include the MLP
spooler, which is an implementation of the System-V lp family of printing
commands (hereafter called lp).
lp is considerably more sophisticated than the lpr commands. It permits
you to have multiple printers of the same type (instead of just one laser
printer and one line printer, as under lpr), which can be plugged into
serial or parallel ports. It supports prioritization of printing jobs
(that is, you can give some users or some types of jobs higher priority
than others), lets each user set a default printer for his jobs, allows
users to reprint their jobs easily, and allows applications to customize
their output to take advantage of special printer features. It even
supports local printing -- that is, it will format and print output onto a
printer that is plugged into a terminal's auxiliary port.
lp's commands resemble those used by UNIX System V to control printing, so
this system can work more easily with third-party applications. Note,
however, that the MLP implementation of lp does differ in some important
respects from the System-V original; therefore, users who have used lp
under UNIX should pay close attention to the following descriptions.
lp consists of the following commands:
cancel Cancel the printing of a job
chreq Change priority, lifetime, or printer for a job
lp Spool one or more files for printing
lpadmin Administer the print-spooler system
lpsched Print jobs spooled with command lp; turn on printer daemon
lpshut Stop the printer daemon
lpstat Give the status of printer or print request
pclfont Prepare a PCL font for downloading via MLP
reprint Reprint a spooled print job
route Let a user change his default printer
Each of these commands is described in its own Lexicon entry.
lp uses the following directories:
/usr/spool/mlp/backend
This directory holds the programs and scripts used to
manage printers.
/usr/spool/mlp/queue
This directory holds all print requests.
/usr/spool/mlp/route
This directory holds files that name each user's
default printer.
lp's behavior is set by the contents of the following files:
/usr/spool/mlp/controls
This file holds lp's configuration data base. This
data base links a printer by name to the device through
which it is accessed, and to the configuration script
(if any) with which its input is massaged. For
information on how to modify it, see the Lexicon entry
for controls.
/usr/spool/mlp/log This file logs lp's activity.
/usr/spool/mlp/status
This file gives the status of each defined printer.
To use lp, you must first use the command lpadmin to build a description
file for each class of printer that you have plugged into your system. The
description file names the class of printer (e.g., ``epson'' or
``laserjet'') and gives the information lp needs to manipulate input to
the printer. For example, a script may include a stty command to set the
port into a special mode, and one or more commands for filtering the input
so it will print properly. A backend script can invoke commands like prps
or epson to process text for printing. lp can perform sophisticated
filtration; for example, it can correctly handle PostScript code that
prints images or bar codes. See the Lexicon entry for lpadmin for more
details on these scripts.
You must then use lpadmin to link a given printer, by name, to the device
through which it is accessed. You must have first identified the port into
which each printer is plugged, as described above. These links are stored
in file /usr/spool/mlp/controls. If you have prepared a configuration
script for this printer's type, then you must link it to the given printer
as well. For example, if you have prepared a configuration script for all
PostScript printers and named it postscript, then you must link that script
to every PostScript printer whose input you want to be massaged in this
manner. Unlike the lpr printing system, lp lets you attach to your
computer more than one printer of each type.
One last point: each ``printer'' should identify a given physical device
plus a given means of accessing it. Thus, one physical printer can have
more than one name if you plan to access it in more than one manner. See
the Lexicon entry for lpadmin for more information on this topic.
Note that if a printer is a ``local printer'' -- that is, a printer plugged
into the auxiliary port of the terminal that the user is using, the termcap
description for that terminal must define the variables PS (print start)
and PN (print end). Each printer's description file is stored in directory
/usr/spool/mlp/backend.
You can use the command route to assign a default printer to each user. If
the user has set a default printer for himself and if he does not name a
printer on the lp command line, the output goes to that default printer.
If the user has not set a default printer for himself and does not name a
printer on his lp command line, the output goes to the system's default
printer. This feature is an extension to the version of lp that is
implemented by UNIX System V.
To spool a job for printing, use the command lp. A job consists either of
one or more files, or of text read from the standard input. lp prefaces
the job with a header that describes where and how the job is to be
printed, then copies it into directory /usr/spool/mlp/queue. The name that
lp gives the spooled job reflects its status, that is, the order in which
it should be printed relative to other jobs that user has spooled. This
allows each user to give a priority to the jobs that he has spooled.
Each job resides in the spooling directory until the printer daemon lpsched
reads it and prints it. lpsched selects jobs for printing based on their
relative priority, as shown in their names. It finds where the job is to
be printed by reading its header; then it opens the description file for
that printer and follows its directions for printing the job. To turn on
the daemon, use the command lpsched by itself; to turn it off, use the
command lpshut. If the spooler is shut down, jobs remain in
/usr/spool/mlp/queue until you reawaken the daemon by issuing the command
lpsched.
To see what files are being printed where, use the command lpstat. To
cancel a printing request, use the command cancel.
A job remains ``alive'' in /usr/spool/mlp/queue until its ``life'' has
expired; the life is set in its header. There are three types of
``lifetime'': temporary, in which a job survives two hours from the time of
spooling; short-term, in which a job survives 48 hours; and long-term, in
which a job survives 72 hours. The default is short-term. When a job's
life expires, lpsched removes it. A user can use the command chreq to
change a job's lifetime or priority; or redirect it from one printer to
another. While a job lives in the spool directory, a user can use the
command reprint to reprint it. He can also use the command route to change
his default printer.
Note that you should be very careful that jobs that include sensitive
information -- e.g., the payroll checks or your resume -- do not linger in
spool directory, where other users can reprint them. For information on
resetting a job's lifetime, see the Lexicon entries for chreq and MLP_LIFE.
You can change the default definitions of temporary, short-term, and long-
term by editing controls. See its entry in the Lexicon for more
information. Caveat utilitor!
The following environmental variables affect lp's default behavior:
MLP_COPIES The number of copies to print.
MLP_FORMLEN The number of lines on the page to be printed.
MLP_LIFE The ``lifespan'' of a spooled file.
MLP_PRIORITY The default priority to give each spooled file.
MLP_SPOOL Set a number of user-specific variable, such as title of
document, type of document, and data base.
These variables can be set either by a user, or embedded in a script. Each
is detailed in its own Lexicon entry.
See Also
Administering COHERENT,
hpr,
lp,
lp [device driver],
lpr,
lpsched
Notes
When you link /dev/lp or /dev/hp to a device, it normally is linked to a
``cooked'' device, e.g., /dev/hp. This works correctly for character-based
output, such as text (or PostScript files); however, if you are downloading
binary data to the printer, such as graphics or fonts, be sure to use the
``raw'' device, e.g., /dev/rhp. Passing binary information through a
``cooked'' device will garble the data and distort the resulting image.
Some COHERENT 4.2 customers have experienced printing problems, including
no printing, slow printing, or printing stops after a line or two. To fix
this, one needs to do the following steps in exact order;
1. Edit file /etc/conf/install_conf/keeplist.
2. Change the last line so that it reads as follows:
echo '-I SHMMNI:SEMMNI:NMSQID:LPWAIT:LPTIME:LPTEST'
3. Type the following command to build a new COHERENT kernel:
/etc/conf/bin/idmkcoh -o /testcoh
4. Shutdown and reboot with the new kernel.
5. Log in as the superuser root.
6. Set the kernel variables that control discipline of the printer. The
driver uses a hybrid busy-wait/timeout discipline, to efficiently
support in a multi-tasking environment a variety of printers whose
buffers come in a multiplicity of sizes.
The variable LPWAIT sets the time for which the processor waits for the
printer to accept the next character. If the printer is not ready
within the LPWAIT period, the processor then resumes normal processing
for the number of ticks set by the kernel variable LPTIME. Thus, setting
LPWAIT to an extremely large number (e.g., 1,000) and LPTIME to a very
small number (e.g., one) results in a fast printer, but leaves very few
cpu cycles available for anything else. Conversely, setting LPWAIT to a
small number (e.g., 50) and LPTIME to a large number (e.g., five)
results in efficient multi-tasking but also results in a slow printer
unless the printer itself contains a buffer (as is normal with all but
the least expensive printers). By default, LPWAIT is set to 400 and
LPTIME to four. We recommend that you set LPWAIT to no less than 50 and
no more than 1,000 and LPTIME to no less than one.
The variable LPTEST determines wether the device driver checks to see if
the printer is in an ``on-line'' condition before it uses the device.
If your printer does not support this signal, you must set LPTEST to
zero.
To reset the values of LPWAIT, LPTIME, and LPTEST, edit file
/etc/conf/mtune and set the parameters LPWAIT_SPEC, LPTIME_SPEC, and
LPTEST_SPEC to the values that you want. Then use the command
/etc/conf/bin/idmkcoh to build a new kernel. For details on this
command, see its entry in the Lexicon. One word of caution to the wary:
be sure to name your new kernel something innocuous, such as cohtest, to
ensure that you do not clobber your current working kernel.
7. Reboot the new kernel and try printing again.
8. If your printer still exhibits problems, try increasing or decreasing
the values of LPTIME and LPWAIT. Remember, each time you build a new
kernel kernel, you must reboot in order for the new variables to take
effect.
The MLP printer spooler is distributed under license from Magnetic Data
Operations, 9400B Two Notch Road, Columbia, SC 29223.
The message
cannot open device /dev/lp
from lpr means either that the printer is not turned on, or that the device
/dev/lp is not linked to the correct parallel-port device. Use the
directions given above to find and link the correct device. The same
applies when you receive this message from hpr.
