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.HTML "A Guide to the Lp Printer Spooler

.TL

A Guide to the Lp

Printer Spooler

.AU

Paul Glick

pg@plan9.bell-labs.com

.AB

.PP

.I Lp

is a collection of programs used to provide an easy-to-use

interface for printing a variety of document types on a variety

of printers.

.I Lp

is the glue that connects various document language

translators and printer communication programs together so that

the users may have a consistent view of printers.

Most of the glue

is shell script, which can be easily modified.

The user need not

specify options to get sensible output in most cases.

.I Lp

is described here

so that others may make additions and changes.

.AE

\" .2C

.NH

Introduction

.PP

.I Lp

is used to format and print data on a variety of output devices.

The need for

.I lp

was rooted in the inability of other printer spoolers to do simple

tasks without a great deal of user specification of options.

At the time

.I lp

was written, there were several printer

languages, such as ImPress and PostScript, and

an internally developed printer that would accept

.I troff

output.

Now, all our printers take PostScript,

but printers that use HPCL and HPGL abound and

support for those printers may be added easily.

A great deal of what underlies

.I lp

is taken from BSD's

.I lpr

and System V's

.I lp .

The important features of this system are that most of the programs

are easily modified shell scripts and the user need not

learn to use the large amount of underlying software developed by others.

.I Lp

runs under Plan 9 and several flavors of

UNIX.

This document deals with

.I lp

as it relates to Plan 9.

.I Lp

was developed using both Datakit and Ethernet to transport data between machines.

Now only the Ethernet transport mechanism remains.

.PP

Text, graphics, and formatted text files are appropriately processed and

placed into a spool directory from which they are taken to be printed by a daemon process.

Additional functions include checking the status of a printer queue

and removing jobs from the printer queue.

.PP

All the shell scripts (see

.I rc (1))

associated with

.I lp

reside in the spool directory

.CW /sys/lib/lp

except for the

.I lp

command itself, which resides in

.CW /rc/bin .

Commands related to

.I lp

that are not shell scripts can most often be found

in

.CW /$cputype/bin/aux .

The directory where all the

.I lp

scripts  reside is defined within

.I lp

by the shell variable

.CW LPLIB .

In the remainder of this document, file names will be specified

with this shell variable as their root.

.NH

Usage

.PP

.I Lp

requires an output device to be specified

before it will process input.

This can be done in any of three ways described here.

.IP 1)

The file

.CW $LPLIB/defdevice

may contain the name of a default output device.

This may not be practical for environments where

there are many printers.

.IP 2)

The user's environment variable

.CW LPDEST

may be set to the name of the device to be used.

This is often a more practical solution when there are several printers

available.

This overrides a

.CW defdevice

specification.

.IP 3)

The

.CW -d

.I printer

option to the

.I lp

command specifies

.I printer

as the device to which output should be directed, overriding the

previous two specifications.

.PP

.ti 0

If

.I printer

is

.CW ? ,

a list of printers and other information in the

.CW devices

file is printed, as shown in Figure 1.

Quote the question mark to prevent it from being

interpreted by the shell language as a metacharacter.

\" .1C

.KF

.P1

% lp -d'?'

device   location  host             class

fn       2C-501    helix            post/2+600dpi+duplex

pcclone  -         -                post+nohead

peacock  2C-501    cetus            post/2+300dpi+nohead+color

ps83     st8_fl3   rice             post+300dpi+reverse

psu      2C-501    cetus            post/2+1200dpi

     .

     .

     .

%

.P2

.ce

.I "Figure 1.  Sample listing of installed printers"

.KE

.PP

Normally,

.I lp

uses the

.CW file

command to figure out what type of input it is receiving.

This is done within the

.CW generic

process which is discussed later in this paper in the

.B "Process directory"

section.

To select a specific input processor the

\f(CW-p\fP\fIprocess\fP

option is used where

.I process

is one of the shell scripts in the

.CW process

directory.

.LP

Troff

output can be printed, in this case, on printer

.I fn

with

.P1

% troff -ms lp.ms | lp -dfn

.P2

.LP

A file can be converted to PostScript using the pseudo-printer

.CW stdout :

.P1

% troff -ms lp.ms | lp -dstdout > lp.ps

.P2

LaTeX (and analogously TeX)

documents are printed in two steps:

.P1

% latex lp.tex

     .

     .

% lp lp.dvi

     .

     .

%

.P2

LaTeX

produces a `.dvi' file and

does not permit the use of a pipe

connection to the standard input of

.I lp .

To look at the status and queue of a device, use

.CW -q :

.P1

% lp -dpsu -q

daemon status:

:  67.17% sent

printer status:

%%[ status: busy; source: lpd ]%%

queue on cetus:

job		user	try	size

rice29436.1	pg	0	17454

slocum17565.1	ches	1	49995

%

.P2

This command can print the status and queue of the local

and remote hosts.

Administrators should be advised that working in an environment where the

.I lp

spool directory is shared among the local and remote hosts,

no spooling should be done on the local hosts.

The format of the status and queue printout is up to the administrator.

The job started above can be killed with

.CW -k :

.P1

$ lp -dpsu -k rice29436.1

rice29436.1 removed from psu queue on cetus

.P2

.NH

Options

.PP

There are options available to modify the way in which a job is handled.

It is the job of the

.I lp

programs to convert the option settings so they may be used by each of the

different translation and interface programs.

Not all options are applicable to all printer environments.

Table 1 lists the standard

.I lp

options, the shell variable settings, and description of the options.

\" .1C

.KF

.sp

.in 0

.TS

center;

c | c s s | c

c | c c c | c

lfCWp-2 | lfCWp-2 cfCWp-2 cfCWp-2 | lp-2w(3i).

=

option	shell variable	action

\^	name	default	set	\^

_

-D	DEBUG	N	1	turn on debugging mode.

_

-H	NOHEADER	N	1	suppress header page.

_

-L	LAND	N	1	make long page dimension horizontal.

_

-M \fImach\fP	LPMACHID	N	\fImach\fP	set the source machine name.

_

-Q	QONLY	N	1	do not execute daemon; for debugging.

_

-c \fIn\fP	COPIES	N	\fIn\fP	number of copies to be printed.

_

-d \fIprinter\fP	LPDEST	U	\fIprinter\fP	set job destination; override other settings.

_

-f \fIfont.pt\fP	FONT	N	\fIfont\fP	set font style and point size for printing.

	POINT	N	\fIpt\fP

_

-i \fIn\fP	IBIN	N	\fIn\fP	T{

select input paper tray options.

The argument given is dependent on the printer type.

A number can be given to select a particular tray and/or

.CW simplex

or

.CW duplex

may be used to get single or double sided output, where

applicable.

Multiple options should be separated by commas.

T}

_

-k	KILLFLAG	0	1	T{

take non-option arguments as job numbers to be removed from queue.

T}

_

-l \fIn\fP	LINES	N	\fIn\fP	T{

for printed data, the number of lines per logical page.

T}

_

-m \fIf\fP	MAG	N	\fIf\fP	T{

magnify the image by a factor \fIf\fP.

The factor should be a positive real number.

T}

_

-n \fIn\fP	NPAG	N	\fIn\fP	T{

put \fIn\fP logical pages on a single physical page.

A simple algorithm is used to pack the pages.

T}

_

-o \fIlist\fP	OLIST	N	\fIlist\fP	T{

print only those pages specified in the list.

The list may be a sequence of numbers or ranges separated by commas.

A range is a pair of numbers separated by a hyphen.

T}

_

-p \fIproc\fP	LPPROC	L	\fIproc\fP	T{

use the preprocessor \fIproc\fP instead of the preprocessor given

in the

.CW devices

file for this printer.

T}

_

-q	LPQ	N	1	T{

print the status and queue.

T}

_

-r	REVERSE	L	1	T{

this toggles the

.CW REVERSE

flag, changing whether or not page reversal should occur in preprocessing.

Page reversal is needed if a printer delivers pages face up.

The keyword

.CW reverse

can be placed in the

.I lpclass

field of the

.CW devices

file.

If a document has already been processed this flag has no effect.

T}

_

-u \fIuser\fP	LPUSERID	U	\fIuser\fP	T{

change the user id that appears on the cover page.

T}

_

-x \fIoffset\fP	XOFF	N	\fIoffset\fP	T{

move the image \fIoffset\fP inches to the right.

A negative \fIoffset\fP will move the image to the left.

The \fIoffset\fP may be any reasonable real number.

T}

_

-y \fIoffset\fP	YOFF	N	\fIoffset\fP	T{

same as for

.CW -x

except a positive offset will move the image down.

T}

_

.T&

l l cp-2 lp-2 s

l l cfCWp-2 lp-2 s.

.vs -2p

		default	setting definition

		N	set to the null string (`') initially in \fIlp\fP.

		L	set from printer entry in \f(CW\\s-\\n(XPdevices\\s+\\n(XP\fP file.

		U	set from the user's environment.

.vs +2p

.TE

.sp

.ce

.I "Table 1. Lp Option List"

.sp

.ll \\n(LLu

.KE

\" .2C	

.NH

Devices file

.PP

The

.CW devices

file is found in the spool directory.

Each line in the file is composed of 12 fields, separated

by tabs or spaces, that describe the attributes

of the printer and how it should be serviced.

Within the

.CW lp

command, a shell variable is set for each attribute;

the following list describes them:

.IP "\f(CW\s-\n(XPLPDEST\s+\n(XP\fP " 12

is the name of the device as given to

.I lp

with the

.CW -d

option

or as specified by the shell environment variable

.CW LPDEST

or as specified by

the file

.CW $LPLIB/defdevice .

This name is used in creating directories and log files that are associated with

the printers operation.

.IP "\f(CW\s-\n(XPLOC\s+\n(XP\fP "

just describes where the printer is physically located.

.IP "\f(CW\s-\n(XPDEST_HOST\s+\n(XP\fP "

is the host from which the files are printed.

Files may be spooled on other machines before being transferred to the

destination host.

.IP "\f(CW\s-\n(XPOUT_DEV\s+\n(XP\fP "

is the physical device name or network address needed by the printer daemon

to connect to the printer.

This field depends on the requirements of the daemon and may contain a `\(en'

if not required.

.IP "\f(CW\s-\n(XPSPEED\s+\n(XP\fP "

is the baud rate setting for the port.

This field depends on the requirements of the daemon and may contain a `\(en'

if not required.

.IP "\f(CW\s-\n(XPLPCLASS\s+\n(XP\fP "

is used to encode minor printer differences.

The keyword

.CW reverse

is used by some of the preprocessors

to reverse the order the pages are printed to accommodate different output

trays (either face up or face down).

The keyword

.CW nohead

is used to suppress the header page.

This is used for special and color printers.

The keyword

.CW duplex

is used to coax double sided output from duplex printers.

.IP "\f(CW\s-\n(XPLPPROC\s+\n(XP\fP "

is the command from the

.CW LPLIB/process

directory to be used to convert input to a format

that will be accepted by the device.

The preprocessor is invoked by the spooler.

.IP "\f(CW\s-\n(XPSPOOLER\s+\n(XP\fP "

is the command from the

.CW LPLIB/spooler

directory which will select files using the

.CW SCHED

command and invoke the

.CW LPPROC

command, putting its output

into the remote spool directory.

The output is sent directly to the spool directory on the

destination machine to avoid conflicts when client and

server machines share spool directories.

.IP "\f(CW\s-\n(XPSTAT\s+\n(XP\fP "

is the command from the

.CW LPLIB/stat

directory that prints the status of the device and the list of jobs

waiting on the queue for the device.

The status information depends on what is available from the printer

and interface software.

The queue information should be changed to show information

useful in tracking down problems.

The

.CW SCHED

command is used to show the jobs in the order

in which they will be printed.

.IP "\f(CW\s-\n(XPKILL\s+\n(XP\fP "

is the command from the

.CW LPLIB/kill

that removes jobs from the queue.

The jobs to be removed are given as arguments to the

.I lp

command.

When possible, it should also abort the currently running job

if it has to be killed.

.IP "\f(CW\s-\n(XPDAEMON\s+\n(XP\fP "

is the command from the

.CW LPLIB/daemon

that is meant to run asynchronously to remove

jobs from the queue.

Jobs may either be passed on to another host or sent to the

printing device.

.I Lp

always tries to start a daemon process when one is specified.

.IP "\f(CW\s-\n(XPSCHED\s+\n(XP\fP "

is the command from the

.CW LPLIB/sched

that is used to present the job names to the

daemon and stat programs

in some order, e.g., first-in-first-out, smallest first.

.NH

Support programs

.PP

The following sections describe the basic functions of the programs

that are found in the subdirectories of

.CW $LPLIB .

The programs in a specific directory vary with the

type of output device or networks that have to be used.

.NH 2

Process directory

.PP

The

.CW generic

preprocessor

is the default preprocessor for most printers.

It uses the

.I file (1)

command to determine the format of the input file.

The appropriate preprocessor is then selected to transform the

file to a format suitable for the printer.

.PP

Here is a list of some of the preprocessors and

a description of their function.

A complete list of preprocessors and their descriptions can be found in the manual page

.I lp (8).

.sp

.IP \f(CWdvipost\fP 14

Converts TeX or LaTeX output (\f(CW.dvi\fP files) to PostScript

.IP \f(CWppost\fP

Converts UTF text to PostScript.

The default font is Courier with Lucida fonts filling in

the remainder of the (available) Unicode character space.

.IP \f(CWtr2post\fP

Converts (device independent) troff output for the device type

.CW utf .

See

.CW /sys/lib/troff/font/devutf

directory for troff font width table descriptions.

See also the

.CW /sys/lib/postscript/troff

directory for mappings of

troff

.CW UTF

character space to PostScript font space.

.IP \f(CWp9bitpost\fP

Converts Plan 9 bitmaps (see

.I bitfile (9.6))

to PostScript.

.IP \f(CWg3post\fP

Converts fax (CCITT-G31 format) to PostScript.

.IP \f(CWhpost\fP

Does header page processing and page reversal processing, if

necessary.

Page reversal is done here so the header page always comes

out at the beginning of the job.

Header page processing is very location-dependent.

.NH 2

Spool directory

.PP

The

.CW generic

spooler is responsible for executing the preprocessor

and directing its output to a file in the printer's queue.

An additional file is created containing information such as the system name,

user id, job number, and number of times this job was attempted.

.PP

Certain printer handling programs do not require separate

preprocessing and spooling.

For such circumstances a

.CW nospool

spooler is available that just executes the preprocessing program.

The processing and spooling functions are assumed by this program and the output is sent to

.CW OUT_DEV

or standard output if

.CW OUT_DEV

is '-'.

.PP

The

.CW pcclone

spooler is used to send print jobs directly to a printer connected

to a 386 compatible printer port (See

.I lpt (3)).

.NH 2

Stat directory

.PP

The function of the shell scripts in the

.CW stat

directory is to present status information about the

printer and its queue.

When necessary, the

.CW stat

scripts may be designed

to return information about the local queue as well as the remote queue.

This is not done on Plan 9 because many systems share the same queue directory.

The scheduler is used to print the queue in the order in which the jobs

will be executed.

.NH 2

Kill directory

.PP

The

.CW kill

scripts receive command line arguments passed to them by

.I lp

and remove the job and id files which match the arguments

for the particular queue.

When a job is killed, the generic kill procedure:

.IP 1)

kills the daemon for this queue if the job being killed

is first in the queue,

.IP 2)

removes the files associated with the job from the queue,

.IP 3)

attempts to restart the daemon.

.NH 2

Daemon directory

.PP

The

.CW daemon

shell scripts are the last to be invoked by

.I lp

if the

.CW -Q

option has not been given.

The daemon process is executed asynchronously

with its standard output and standard error appended to

the printer log file.

The log file is described in a subsequent section.

Because the daemon runs asynchronously, it must

catch signals that could cause it to terminate abnormally.

The daemon first checks to see that it is the only one running

by using the

.CW LOCK

program found in the

.CW /$cputype/bin/aux

directory.

The

.CW LOCK

command creates a

.CW LOCK

file in the printer's queue directory.

The daemon then executes the scheduler to obtain the name of the

next job on the queue.

.PP

The processing of jobs may entail transfer to another host

or transmission to a printer.

The details of this are specific to the individual daemons.

If a job is processed without error, it is removed from the queue.

If a job does not succeed, the associated files may be

moved to a printer specific directory in

.CW $LPLIB/prob .

In either case, the daemon can make an entry in the printer's

log file.

Before exiting, the daemon should clean up lock files by calling

.CW UNLOCK .

.PP

Several non-standard daemon programs have been designed

to suit various requirements and whims.

One such program announces job completion and empty paper trays

by causing icons to appear in peoples'

.CW seemail

window.

Another, using a voice synthesizer, makes verbal announcements.

Other daemons may be designed to taste.

.NH 2

Sched directory

.PP

The scheduler must decide which job files should be executed and

in what order.

The most commonly used scheduler program is

.CW FIFO ,

which looks like this:

.P1

ls -tr $* | sed -n -e 's/.*  *//' \e

  -e '/^[0-9][0-9]*\.[1-9][0-9]*$/p'

.P2

This lists all the job files in this printer's queue in modification

time order.

Jobs entering the queue have a dot (.) prefixed to their name

to keep the scheduler from selecting them before they are complete.

.NH

Where Things Go Wrong

.PP

There are four directories where

.I lp

writes files.

On the Plan 9 release these directories may be found

in a directory on a scratch filesystem that is not

backed-up.

This directory is

.CW /n/emelieother/lp .

It is built on top of a file system

.CW other

that is mounted on the file server

.CW emelie .

The four directories in

this scratch directory

are

.CW log ,

.CW prob ,

.CW queue ,

and

.CW tmp .

.I Lp

binds (see

.I bind (1))

the first three into the directory

.CW /sys/lib/lp

for its processes and their children.

The

.CW tmp

directory is bound to the

.CW /tmp

directory so that the lp daemons, which run as user `none',

may write into this directory.

.PP

On any new installation, it is important that these directories

be set up and that the

.I /rc/bin/lp

command be editted to reflect the change.

If you do not have a scratch filesystem for these directories,

create the four directories

.CW log ,

.CW prob ,

.CW queue ,

and

.CW tmp

in

.CW $LPLIB

.CW (/sys/lib/lp)

so that they are writable by anyone.

.NH 2

Log directory

.PP

The log files for a particular

.I printer

appear in a subdirectory of the spool directory

\f(CWlog\fP/\fIprinter\fP.

There are currently two types of log files.

One is for the daemon to log errors and successful completions

of jobs.

These are named

.I printer.day

where

.I day

is the three letter abbreviation for the day of the week.

These are overwritten once a week to avoid the need for regular

cleanup.

The other type of log file contains the status of the printer and

is written by the program that communicates with the printer itself.

These are named

\fIprinter\fP.\f(CWst\fP.

These are overwritten with each new job and are saved in the

.CW $LPLIB/prob

directory along with the job under circumstances described below.

When a printer does not appear to be functioning these files are the

place to look first.

.NH 2

Prob directory

.PP

When a job fails to produce output,

the log files should be checked for any obvious problems.

If none can be found, a directory with full read and write permissions

should be created with the name of the printer in the

.CW $LPLIB/prob

directory.

Subsequent failure of a job will cause the daemon to leave a

copy of the job and the printer communication log in

\f(CW$LPLIB/prob/\fP\fIprinter\fP

directory.

It is common for a printer to enter states from which

it cannot be rescued except by manually cycling the power on the printer.

After this is done the print daemon should recover by itself

(give it a minute).

If it does not recover, remove the

.CW LOCK

file from the printer's spool directory to kill the daemon.

The daemon will have to be restarted by sending another job

to the printer.

For PostScript printers just use:

.P1

echo '%!PS' | lp

.P2

.NH 2

Repairing Stuck Daemons

.PP

There are conditions that occur which are not handled

by the daemons.

One such problem can only be described as the printer entering a

comatose state.

The printer does not respond to any messages sent to it.

The daemon should recover from the reset and an error message

will appear in the log files.

If all else fails, one can kill the first job in the queue

or remove the

.CW LOCK

file from the queue directory.

This will kill the daemon, which will have to be restarted.

.NH

Interprocessor Communication

.PP

A Plan 9 CPU server can be set up as a printer's spooling host.

That is, the machine where jobs are spooled and from which those jobs

are sent directly to the printer.

To do this, the CPU must listen on TCP port 515 which is the well known

port for the BSD line printer daemon.

The file

.CW /rc/bin/service/tcp515

is executed when a call comes in on that port.

The Plan 9

.CW lpdaemon

will accept jobs sent from BSD LPR/LPD systems.

The

.CW /$cputype/bin/aux/lpdaemon

command is executed from the service call and it accepts print jobs, requests for status,

and requests to kill jobs.

The command

.CW /$cputype/bin/aux/lpsend

is used to send jobs

to other Plan 9 machines and is usually called from

within a spooler or daemon script.

The command

.CW /$cputype/bin/aux/lpdsend

is used to send jobs

to machines and printers that use the BSD LPR/LPD protocol and is also usually called from

within a spooler or daemon script.

.NH

Acknowledgements

.PP

Special thanks to Rich Drechsler for supplying and maintaining most of

the PostScript translation and interface programs,

without which

.I lp

would be an empty shell.

Tomas Rokicki provided the

TeX

to PostScript

translation program.

.NH

References

.LP

[Camp86] Ralph Campbell,

``4.3BSD Line Printer Spooler Manual'', UNIX System Manager's Manual,

May, 1986, Berkeley, CA

.br

[RFC1179] Request for Comments: 1179, Line Printer Daemon Protocol, Aug 1990

.br

[Sys5] System V manual, date unknown