This section describes filters for printing specially formatted files, header pages, printing across networks, and restricting and accounting for printer usage.
Although LPD handles network protocols, queuing, access control, and other aspects of printing, most of the real work happens in the filters. Filters are programs that communicate with the printer and handle its device dependencies and special requirements. In the simple printer setup, we installed a plain text filter—an extremely simple one that should work with most printers (section Installing the Text Filter).
However, in order to take advantage of format conversion, printer accounting, specific printer quirks, and so on, you should understand how filters work. It will ultimately be the filter's responsibility to handle these aspects. And the bad news is that most of the time you have to provide filters yourself. The good news is that many are generally available; when they are not, they are usually easy to write.
Also, FreeBSD comes with one,
/usr/libexec/lpr/lpf
, that works with
many printers that can print plain text. (It handles
backspacing and tabs in the file, and does accounting, but
that is about all it does.) There are also several filters
and filter components in the FreeBSD Ports Collection.
Here is what you will find in this section:
Section How Filters Work, tries to give an overview of a filter's role in the printing process. You should read this section to get an understanding of what is happening “under the hood” when LPD uses filters. This knowledge could help you anticipate and debug problems you might encounter as you install more and more filters for each of your printers.
LPD expects every printer to be able to print plain text by default. This presents a problem for PostScript® printers (or other language-based printers) which cannot directly print plain text. Section Accommodating Plain Text Jobs on PostScript® Printers tells you what you should do to overcome this problem. You should read this section if you have a PostScript® printer.
PostScript® is a popular output format for many programs. Some people even write PostScript® code directly. Unfortunately, PostScript® printers are expensive. Section Simulating PostScript® on Non PostScript® Printers tells how you can further modify a printer's text filter to accept and print PostScript® data on a non PostScript® printer. You should read this section if you do not have a PostScript® printer.
Section Conversion
Filters tells about a way you can automate the
conversion of specific file formats, such as graphic or
typesetting data, into formats your printer can
understand. After reading this section, you should be
able to set up your printers such that users can type
lpr
to print troff
data, or -t
lpr
to
print TeX DVI data, or -d
lpr
to print raster image
data, and so forth. The reading of this section is
recommended.-v
Section Output Filters tells all about a not often used feature of LPD: output filters. Unless you are printing header pages (see Header Pages), you can probably skip that section altogether.
Section lpf:
a Text Filter describes lpf
,
a fairly complete if simple text filter for line
printers (and laser printers that act like line
printers) that comes with FreeBSD. If you need a quick
way to get printer accounting working for plain text,
or if you have a printer which emits smoke when it sees
backspace characters, you should definitely consider
lpf
.
A copy of the various scripts described below can be
found in the /usr/share/examples/printing
directory.
As mentioned before, a filter is an executable program started by LPD to handle the device-dependent part of communicating with the printer.
When LPD wants to print a
file in a job, it starts a filter program. It sets the
filter's standard input to the file to print, its standard
output to the printer, and its standard error to the error
logging file (specified in the lf
capability in /etc/printcap
, or
/dev/console
by
default).
Which filter LPD starts and
the filter's arguments depend on what is listed in the
/etc/printcap
file and what arguments
the user specified for the job on the lpr(1) command
line. For example, if the user typed
lpr
,
LPD would start the troff filter,
listed in the -t
tf
capability for the
destination printer. If the user wanted to print plain
text, it would start the if
filter (this
is mostly true: see Output Filters for
details).
There are three kinds of filters you can specify in
/etc/printcap
:
The text filter, confusingly called the input filter in LPD documentation, handles regular text printing. Think of it as the default filter. LPD expects every printer to be able to print plain text by default, and it is the text filter's job to make sure backspaces, tabs, or other special characters do not confuse the printer. If you are in an environment where you have to account for printer usage, the text filter must also account for pages printed, usually by counting the number of lines printed and comparing that to the number of lines per page the printer supports. The text filter is started with the following argument list:
filter-name
[-c] -w
width
-l
length
-i
indent
-n
login
-h
host
acct-file
where
-c
appears if the job is submitted with
lpr
-l
width
is the value from the pw
(page width) capability specified in
/etc/printcap
, default
132
length
is the value from the pl
(page length) capability, default 66
indent
is the amount of the indentation from
lpr
,
default 0-i
login
is the account name of the user printing the file
host
is the host name from which the job was submitted
acct-file
is the name of the accounting file from the
af
capability.
A conversion filter converts a specific file format into one the printer can render onto paper. For example, ditroff typesetting data cannot be directly printed, but you can install a conversion filter for ditroff files to convert the ditroff data into a form the printer can digest and print. Section Conversion Filters tells all about them. Conversion filters also need to do accounting, if you need printer accounting. Conversion filters are started with the following arguments:
filter-name
-x
pixel-width
-y
pixel-height
-n
login
-h
host
acct-file
where pixel-width
is
the value from the px
capability
(default 0) and pixel-height
is the value from the py
capability
(default 0).
The output filter is used only if there is no text filter, or if header pages are enabled. In our experience, output filters are rarely used. Section Output Filters describes them. There are only two arguments to an output filter:
filter-name
-w
width
-l
length
which are identical to the text filters
-w
and -l
arguments.
Filters should also exit with the following exit status:
If the filter printed the file successfully.
If the filter failed to print the file but wants LPD to try to print the file again. LPD will restart a filter if it exits with this status.
If the filter failed to print the file and does not want LPD to try again. LPD will throw out the file.
The text filter that comes with the FreeBSD release,
/usr/libexec/lpr/lpf
, takes advantage
of the page width and length arguments to determine when
to send a form feed and how to account for printer usage.
It uses the login, host, and accounting file arguments to
make the accounting entries.
If you are shopping for filters, see if they are LPD-compatible. If they are, they must support the argument lists described above. If you plan on writing filters for general use, then have them support the same argument lists and exit codes.
If you are the only user of your computer and PostScript® (or other language-based) printer, and you promise to never send plain text to your printer and to never use features of various programs that will want to send plain text to your printer, then you do not need to worry about this section at all.
But, if you would like to send both PostScript® and
plain text jobs to the printer, then you are urged to
augment your printer setup. To do so, we have the text
filter detect if the arriving job is plain text or
PostScript®. All PostScript® jobs must start with
%!
(for other printer languages, see
your printer documentation). If those are the first two
characters in the job, we have PostScript®, and can pass
the rest of the job directly. If those are not the first
two characters in the file, then the filter will convert
the text into PostScript® and print the result.
How do we do this?
If you have got a serial printer, a great way to do it
is to install lprps
.
lprps
is a PostScript® printer filter
which performs two-way communication with the printer. It
updates the printer's status file with verbose information
from the printer, so users and administrators can see
exactly what the state of the printer is (such as
toner low or paper
jam). But more importantly, it includes a
program called psif
which detects whether
the incoming job is plain text and calls
textps
(another program that comes with
lprps
) to convert it to PostScript®.
It then uses lprps
to send the job to
the printer.
lprps
is part of the FreeBSD Ports
Collection (see The Ports
Collection). You can install one of the both
print/lprps-a4
and
print/lprps-letter
ports
according to the paper size used. After installing
lprps
, just specify the pathname to the
psif
program that is part of
lprps
. If you installed
lprps
from the Ports Collection, use
the following in the serial PostScript® printer's entry
in /etc/printcap
:
/usr/local/libexec/psif
:The rw
capability should be also
included in order to let LPD to
open the printer in the read-write mode.
If you have a parallel PostScript® printer (and
therefore cannot use two-way communication with the printer,
which lprps
needs), you can use the
following shell script as the text filter:
In the above script, textps
is a
program we installed separately to convert plain text to
PostScript®. You can use any text-to-PostScript® program
you wish. The FreeBSD Ports Collection (see The Ports Collection) includes a
full featured text-to-PostScript® program called
a2ps
that you might want to
investigate.
PostScript® is the de facto standard for high quality typesetting and printing. PostScript® is, however, an expensive standard. Thankfully, Aladdin Enterprises has a free PostScript® work-alike called Ghostscript that runs with FreeBSD. Ghostscript can read most PostScript® files and can render their pages onto a variety of devices, including many brands of non-PostScript® printers. By installing Ghostscript and using a special text filter for your printer, you can make your non PostScript® printer act like a real PostScript® printer.
Ghostscript is in the FreeBSD
Ports Collection, many versions are available, the most
commonly used version is print/ghostscript-gpl
.
To simulate PostScript®, we have the text filter detect if it is printing a PostScript® file. If it is not, then the filter will pass the file directly to the printer; otherwise, it will use Ghostscript to first convert the file into a format the printer will understand.
Here is an example: the following script is a text
filter for Hewlett Packard DeskJet 500 printers. For other
printers, substitute the -sDEVICE
argument
to the gs
(Ghostscript) command. (Type
gs
to get a list of
devices the current installation of
Ghostscript supports.)-h
Finally, you need to notify
LPD of the filter via the
if
capability:
/usr/local/libexec/ifhp
:That is it. You can type
lpr
and
plain.text
lpr
and both should print successfully.whatever.ps
After completing the simple setup described in Simple Printer Setup, the first thing you will probably want to do is install conversion filters for your favorite file formats (besides plain ASCII text).
Conversion filters make printing various kinds of files easy. As an example, suppose we do a lot of work with the TeX typesetting system, and we have a PostScript® printer. Every time we generate a DVI file from TeX, we cannot print it directly until we convert the DVI file into PostScript®. The command sequence goes like this:
%
dvips seaweed-analysis.dvi
%
lpr seaweed-analysis.ps
By installing a conversion filter for DVI files, we can skip the hand conversion step each time by having LPD do it for us. Now, each time we get a DVI file, we are just one step away from printing it:
%
lpr -d
seaweed-analysis.dvi
We got LPD to do the DVI
file conversion for us by specifying the
-d
option. Section Formatting and
Conversion Options lists the conversion
options.
For each of the conversion options you want a printer
to support, install a conversion
filter and specify its pathname in
/etc/printcap
. A conversion filter
is like the text filter for the simple printer setup (see
section Installing
the Text Filter) except that instead of printing
plain text, the filter converts the file into a format
the printer can understand.
You should install the conversion filters you expect to use. If you print a lot of DVI data, then a DVI conversion filter is in order. If you have got plenty of troff to print out, then you probably want a troff filter.
The following table summarizes the filters that
LPD works
with, their capability entries for the
/etc/printcap
file, and how to
invoke them with the lpr
command:
File type | /etc/printcap
capability | lpr option |
---|---|---|
cifplot | cf | -c |
DVI | df | -d |
plot | gf | -g |
ditroff | nf | -n |
FORTRAN text | rf | -f |
troff | tf | -f |
raster | vf | -v |
plain text | if | none, -p , or
-l |
In our example, using
lpr
means the
printer needs a -d
df
capability in its
entry in /etc/printcap
.
Despite what others might contend, formats like
FORTRAN text and plot are probably obsolete. At your
site, you can give new meanings to these or any of the
formatting options just by installing custom filters.
For example, suppose you would like to directly print
Printerleaf files (files from the Interleaf desktop
publishing program), but will never print plot files.
You could install a Printerleaf conversion filter under
the gf
capability and then educate your
users that lpr
mean
“print Printerleaf files.”-g
Since conversion filters are programs you install
outside of the base FreeBSD installation, they should
probably go under /usr/local
. The
directory /usr/local/libexec
is a
popular location, since they are specialized programs
that only LPD will run; regular
users should not ever need to run them.
To enable a conversion filter, specify its pathname
under the appropriate capability for the destination
printer in /etc/printcap
.
In our example, we will add the DVI conversion filter
to the entry for the printer named
bamboo
. Here is the example
/etc/printcap
file again, with
the new df
capability for the printer
bamboo
:
/var/spool/lpd/rattan
:\
:lp=/dev/lpt0
:\
:if=/usr/local/libexec/if-simple
:
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
:sh:sd=/var/spool/lpd/bamboo
:\
:lp=/dev/ttyu5
:ms#-parenb cs8 clocal crtscts:rw:\
:if=/usr/local/libexec/psif
:\
:df=/usr/local/libexec/psdf
:The DVI filter is a shell script named
/usr/local/libexec/psdf
. Here is
that script:
This script runs dvips
in filter
mode (the -f
argument) on standard input,
which is the job to print. It then starts the
PostScript® printer filter lprps
(see section Accommodating
Plain Text Jobs on PostScript® Printers) with
the arguments LPD passed to
this script. The lprps
utility will
use those arguments to account for the pages
printed.
There is no fixed set of steps to install conversion filters, some working examples are described in this section. Use these as guidance to making your own filters. Use them directly, if appropriate.
This example script is a raster (well, GIF file, actually) conversion filter for a Hewlett Packard LaserJet III-Si printer:
It works by converting the GIF file into a portable anymap, converting that into a portable graymap, converting that into a portable bitmap, and converting that into LaserJet/PCL-compatible data.
Here is the /etc/printcap
file
with an entry for a printer using the above filter:
/dev/lpt0
:sh:sd=/var/spool/lpd/teak
:mx#0:\
:if=/usr/local/libexec/hpif
:\
:vf=/usr/local/libexec/hpvf
:The following script is a conversion filter for troff
data from the groff typesetting system for the
PostScript® printer named
bamboo
:
The above script makes use of lprps
again to handle the communication with the printer. If
the printer were on a parallel port, we would use this
script instead:
That is it. Here is the entry we need to add to
/etc/printcap
to enable the
filter:
/usr/local/libexec/pstf
:Here is an example that might make old hands at
FORTRAN blush. It is a FORTRAN-text filter for any
printer that can directly print plain text. We will
install it for the printer teak
:
And we will add this line to the
/etc/printcap
for the printer
teak
to enable this filter:
/usr/local/libexec/hprf
:Here is one final, somewhat complex example. We
will add a DVI filter to the LaserJet printer
teak
introduced earlier. First, the
easy part: updating /etc/printcap
with the location of the DVI filter:
/usr/local/libexec/hpdf
:Now, for the hard part: making the filter. For that,
we need a DVI-to-LaserJet/PCL conversion program. The
FreeBSD Ports Collection (see The Ports
Collection) has one: print/dvi2xx
. Installing this
port gives us the program we need,
dvilj2p
, which converts DVI into
LaserJet IIp, LaserJet III, and LaserJet 2000 compatible
codes.
The dvilj2p
utility makes the
filter hpdf
quite complex since
dvilj2p
cannot read from standard
input. It wants to work with a filename. What is worse,
the filename has to end in .dvi
so
using /dev/fd/0
for standard input is problematic. We can get around that
problem by linking (symbolically) a temporary file name
(one that ends in .dvi
) to
/dev/fd/0
, thereby
forcing dvilj2p
to read from standard
input.
The only other fly in the ointment is the fact that
we cannot use /tmp
for the temporary link. Symbolic links are owned by user
and group bin
. The filter runs as
user daemon
. And the /tmp
directory has the
sticky bit set. The filter can create the link, but it
will not be able clean up when done and remove it since
the link will belong to a different user.
Instead, the filter will make the symbolic link in
the current working directory, which is the spooling
directory (specified by the sd
capability in /etc/printcap
). This
is a perfect place for filters to do their work,
especially since there is (sometimes) more free disk space
in the spooling directory than under
/tmp
.
Here, finally, is the filter:
All these conversion filters accomplish a lot for your printing environment, but at the cost forcing the user to specify (on the lpr(1) command line) which one to use. If your users are not particularly computer literate, having to specify a filter option will become annoying. What is worse, though, is that an incorrectly specified filter option may run a filter on the wrong type of file and cause your printer to spew out hundreds of sheets of paper.
Rather than install conversion filters at all, you
might want to try having the text filter (since it is the
default filter) detect the type of file it has been asked
to print and then automatically run the right conversion
filter. Tools such as file
can be of
help here. Of course, it will be hard to determine the
differences between some file
types—and, of course, you can still provide
conversion filters just for them.
The FreeBSD Ports Collection has a text filter that
performs automatic conversion called
apsfilter
(print/apsfilter
). It can
detect plain text, PostScript®, DVI and almost any kind
of files, run the proper conversions, and print.
The LPD spooling system supports one other type of filter that we have not yet explored: an output filter. An output filter is intended for printing plain text only, like the text filter, but with many simplifications. If you are using an output filter but no text filter, then:
LPD starts an output filter once for the entire job instead of once for each file in the job.
LPD does not make any provision to identify the start or the end of files within the job for the output filter.
LPD does not pass the user's login or host to the filter, so it is not intended to do accounting. In fact, it gets only two arguments:
filter-name
-wwidth
-llength
Where width
is from the
pw
capability and
length
is from the
pl
capability for the printer in
question.
Do not be seduced by an output filter's simplicity. If you would like each file in a job to start on a different page an output filter will not work. Use a text filter (also known as an input filter); see section Installing the Text Filter. Furthermore, an output filter is actually more complex in that it has to examine the byte stream being sent to it for special flag characters and must send signals to itself on behalf of LPD.
However, an output filter is necessary if you want header pages and need to send escape sequences or other initialization strings to be able to print the header page. (But it is also futile if you want to charge header pages to the requesting user's account, since LPD does not give any user or host information to the output filter.)
On a single printer, LPD
allows both an output filter and text or other filters.
In such cases, LPD will start
the output filter to print the header page (see section
Header
Pages) only. LPD then
expects the output filter to stop
itself by sending two bytes to the filter:
ASCII 031 followed by ASCII 001. When an output filter
sees these two bytes (031, 001), it should stop by sending
SIGSTOP
to itself. When
LPD's done running other filters,
it will restart the output filter by sending
SIGCONT
to it.
If there is an output filter but no text filter and LPD is working on a plain text job, LPD uses the output filter to do the job. As stated before, the output filter will print each file of the job in sequence with no intervening form feeds or other paper advancement, and this is probably not what you want. In almost all cases, you need a text filter.
The program lpf
, which we introduced
earlier as a text filter, can also run as an output filter.
If you need a quick-and-dirty output filter but do not want
to write the byte detection and signal sending code, try
lpf
. You can also wrap
lpf
in a shell script to handle any
initialization codes the printer might require.
The program /usr/libexec/lpr/lpf
that comes with FreeBSD binary distribution is a text filter
(input filter) that can indent output (job submitted with
lpr
), allow literal
characters to pass (job submitted with
-i
lpr
), adjust the
printing position for backspaces and tabs in the job, and
account for pages printed. It can also act like an output
filter.-l
The lpf
filter is suitable for many
printing environments. And although it has no capability
to send initialization sequences to a printer, it is easy
to write a shell script to do the needed initialization
and then execute lpf
.
In order for lpf
to do page
accounting correctly, it needs correct values filled in
for the pw
and pl
capabilities in the /etc/printcap
file.
It uses these values to determine how much text can fit on
a page and how many pages were in a user's job. For more
information on printer accounting, see Accounting for Printer
Usage.
If you have lots of users, all of them using various printers, then you probably want to consider header pages as a necessary evil.
Header pages, also known as banner or burst pages identify to whom jobs belong after they are printed. They are usually printed in large, bold letters, perhaps with decorative borders, so that in a stack of printouts they stand out from the real documents that comprise users' jobs. They enable users to locate their jobs quickly. The obvious drawback to a header page is that it is yet one more sheet that has to be printed for every job, their ephemeral usefulness lasting not more than a few minutes, ultimately finding themselves in a recycling bin or rubbish heap. (Note that header pages go with each job, not each file in a job, so the paper waste might not be that bad.)
The LPD system can provide header pages automatically for your printouts if your printer can directly print plain text. If you have a PostScript® printer, you will need an external program to generate the header page; see Header Pages on PostScript® Printers.
In the Simple Printer
Setup section, we turned off header pages by
specifying sh
(meaning “suppress
header”) in the /etc/printcap
file. To enable header pages for a printer, just remove the
sh
capability.
Sounds too easy, right?
You are right. You might have to provide an output filter to send initialization strings to the printer. Here is an example output filter for Hewlett Packard PCL-compatible printers:
Specify the path to the output filter in the
of
capability. See the Output Filters
section for more information.
Here is an example /etc/printcap
file for the printer teak
that we
introduced earlier; we enabled header pages and added the
above output filter:
/dev/lpt0
:sd=/var/spool/lpd/teak
:mx#0:\
:if=/usr/local/libexec/hpif
:\
:vf=/usr/local/libexec/hpvf
:\
:of=/usr/local/libexec/hpof
:Now, when users print jobs to teak
,
they get a header page with each job. If users want to
spend time searching for their printouts, they can suppress
header pages by submitting the job with lpr
; see the Header Page
Options section for more lpr(1)
options.-h
LPD prints a form feed
character after the header page. If your printer uses
a different character or sequence of characters to eject
a page, specify them with the ff
capability in /etc/printcap
.
By enabling header pages, LPD
will produce a long header, a full
page of large letters identifying the user, host, and job.
Here is an example (kelly
printed the
job named “outline” from host
rose
):
LPD appends a form feed after
this text so the job starts on a new page (unless you have
sf
(suppress form feeds) in the
destination printer's entry in
/etc/printcap
).
If you prefer, LPD can make
a short header; specify
sb
(short banner) in the
/etc/printcap
file. The header page
will look like this:
Also by default, LPD prints
the header page first, then the job. To reverse that,
specify hl
(header last) in
/etc/printcap
.
Using LPD's built-in header pages enforces a particular paradigm when it comes to printer accounting: header pages must be free of charge.
Why?
Because the output filter is the only external program
that will have control when the header page is printed that
could do accounting, and it is not provided with any
user or host information or an
accounting file, so it has no idea whom to charge for
printer use. It is also not enough to just “increase
the page count by one” by modifying the text
filter or any of the conversion filters (which do have user
and host information) since users can suppress header pages
with lpr
. They could
still be charged for header pages they did not print.
Basically, -h
lpr
will
be the preferred option of environmentally-minded users,
but you cannot offer any incentive to use it.-h
It is still not enough to have each
of the filters generate their own header pages (thereby
being able to charge for them). If users wanted the option
of suppressing the header pages with lpr
, they will still get them
and be charged for them since LPD
does not pass any knowledge of the -h
-h
option to any of the filters.
So, what are your options?
You can:
Accept LPD's paradigm and make header pages free.
Install an alternative to LPD, such as LPRng. Section Alternatives to the Standard Spooler tells more about other spooling software you can substitute for LPD.
Write a smart output filter.
Normally, an output filter is not meant to do anything
more than initialize a printer or do some simple
character conversion. It is suited for header pages
and plain text jobs (when there is no text (input)
filter). But, if there is a text filter for the plain
text jobs, then LPD will
start the output filter only for the header pages.
And the output filter can parse the header page text
that LPD generates to
determine what user and host to charge for the header
page. The only other problem with this method is that
the output filter still does not know what accounting
file to use (it is not passed the name of the file from
the af
capability), but if you have
a well-known accounting file, you can hard-code that
into the output filter. To facilitate the parsing step,
use the sh
(short header) capability
in /etc/printcap
. Then again, all
that might be too much trouble, and users will certainly
appreciate the more generous system administrator who
makes header pages free.
As described above, LPD can generate a plain text header page suitable for many printers. Of course, PostScript® cannot directly print plain text, so the header page feature of LPD is useless—or mostly so.
One obvious way to get header pages is to have every
conversion filter and the text filter generate the header
page. The filters should use the user and host arguments
to generate a suitable header page. The drawback of this
method is that users will always get a header page, even
if they submit jobs with lpr
.-h
Let us explore this method. The following script takes three arguments (user login name, host name, and job name) and makes a simple PostScript® header page:
Now, each of the conversion filters and the text filter can call this script to first generate the header page, and then print the user's job. Here is the DVI conversion filter from earlier in this document, modified to make a header page:
Notice how the filter has to parse the argument list in order to determine the user and host name. The parsing for the other conversion filters is identical. The text filter takes a slightly different set of arguments, though (see section How Filters Work).
As we have mentioned before, the above scheme, though
fairly simple, disables the “suppress header
page” option (the -h
option) to
lpr
. If users wanted to save a tree (or
a few pennies, if you charge for header pages), they would
not be able to do so, since every filter's going to print a
header page with every job.
To allow users to shut off header pages on a per-job
basis, you will need to use the trick introduced in section
Accounting
for Header Pages: write an output filter that parses
the LPD-generated header page and produces a PostScript®
version. If the user submits the job with
lpr
,
then LPD will not generate a
header page, and neither will your output filter.
Otherwise, your output filter will read the text from
LPD and send the appropriate
header page PostScript® code to the printer.-h
If you have a PostScript® printer on a serial line, you
can make use of lprps
, which comes with
an output filter, psof
, which does the
above. Note that psof
does not charge
for header pages.
FreeBSD supports networked printing: sending jobs to remote printers. Networked printing generally refers to two different things:
Accessing a printer attached to a remote host. You install a printer that has a conventional serial or parallel interface on one host. Then, you set up LPD to enable access to the printer from other hosts on the network. Section Printers Installed on Remote Hosts tells how to do this.
Accessing a printer attached directly to a network. The printer has a network interface in addition to (or in place of) a more conventional serial or parallel interface. Such a printer might work as follows:
It might understand the LPD protocol and can even queue jobs from remote hosts. In this case, it acts just like a regular host running LPD. Follow the same procedure in section Printers Installed on Remote Hosts to set up such a printer.
It might support a data stream network connection. In this case, you “attach” the printer to one host on the network by making that host responsible for spooling jobs and sending them to the printer. Section Printers with Networked Data Stream Interfaces gives some suggestions on installing such printers.
The LPD spooling system has built-in support for sending jobs to other hosts also running LPD (or are compatible with LPD). This feature enables you to install a printer on one host and make it accessible from other hosts. It also works with printers that have network interfaces that understand the LPD protocol.
To enable this kind of remote printing, first install a printer on one host, the printer host, using the simple printer setup described in the Simple Printer Setup section. Do any advanced setup in Advanced Printer Setup that you need. Make sure to test the printer and see if it works with the features of LPD you have enabled. Also ensure that the local host has authorization to use the LPD service in the remote host (see Restricting Jobs from Remote Hosts).
If you are using a printer with a network interface that is compatible with LPD, then the printer host in the discussion below is the printer itself, and the printer name is the name you configured for the printer. See the documentation that accompanied your printer and/or printer-network interface.
If you are using a Hewlett Packard Laserjet then the
printer name text
will automatically
perform the LF to CRLF conversion for you, so you will not
require the hpif
script.
Then, on the other hosts you want to have access to the
printer, make an entry in their
/etc/printcap
files with the
following:
Name the entry anything you want. For simplicity, though, you probably want to use the same name and aliases as on the printer host.
Leave the lp
capability blank,
explicitly (:lp=:
).
Make a spooling directory and specify its location
in the sd
capability.
LPD will store jobs here
before they get sent to the printer host.
Place the name of the printer host in the
rm
capability.
Place the printer name on the printer
host in the rp
capability.
That is it. You do not need to list conversion filters,
page dimensions, or anything else in the
/etc/printcap
file.
Here is an example. The host rose
has
two printers, bamboo
and
rattan
. We will enable users on the host
orchid
to print to those printers. Here is
the /etc/printcap
file for
orchid
(back from section Enabling
Header Pages). It already had the entry for the
printer teak
; we have added entries for
the two printers on the host rose
:
/dev/lpt0
:sd=/var/spool/lpd/teak
:mx#0:\
:if=/usr/local/libexec/ifhp
:\
:vf=/usr/local/libexec/vfhp
:\
:of=/usr/local/libexec/ofhp
:
#
# rattan is connected to rose; send jobs for rattan to rose:
#
rattan|line|diablo|lp|Diablo 630 Line Printer:\
:lp=:rm=rose:rp=rattan:sd=/var/spool/lpd/rattan
:
#
# bamboo is connected to rose as well:
#
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
:lp=:rm=rose:rp=bamboo:sd=/var/spool/lpd/bamboo
:Then, we just need to make spooling directories on
orchid
:
#
mkdir -p
/var/spool/lpd/rattan
/var/spool/lpd/bamboo
#
chmod 770 /var/spool/lpd/rattan
/var/spool/lpd/bamboo
#
chown daemon:daemon /var/spool/lpd/rattan
/var/spool/lpd/bamboo
Now, users on orchid
can print to
rattan
and bamboo
.
If, for example, a user on orchid
typed:
%
lpr -P
bamboo -d
sushi-review.dvi
the LPD system on
orchid
would copy the job to the spooling
directory /var/spool/lpd/bamboo
and
note that it was a DVI job. As soon as the host
rose
has room in its
bamboo
spooling directory, the two
LPDs would transfer the file to
rose
. The file would wait in
rose
's queue until it was finally printed.
It would be converted from DVI to PostScript® (since
bamboo
is a PostScript® printer) on
rose
.
Often, when you buy a network interface card for a printer, you can get two versions: one which emulates a spooler (the more expensive version), or one which just lets you send data to it as if you were using a serial or parallel port (the cheaper version). This section tells how to use the cheaper version. For the more expensive one, see the previous section Printers Installed on Remote Hosts.
The format of the /etc/printcap
file lets you specify what serial or parallel interface to
use, and (if you are using a serial interface), what baud
rate, whether to use flow control, delays for tabs,
conversion of newlines, and more. But there is no way to
specify a connection to a printer that is listening on a
TCP/IP or other network port.
To send data to a networked printer, you need to develop
a communications program that can be called by the text and
conversion filters. Here is one such example: the script
netprint
takes all data on standard input
and sends it to a network-attached printer. We specify the
hostname of the printer as the first argument and the port
number to which to connect as the second argument to
netprint
. Note that this supports
one-way communication only (FreeBSD to printer); many network
printers support two-way communication, and you might want
to take advantage of that (to get printer status, perform
accounting, etc.).
We can then use this script in various filters. Suppose
we had a Diablo 750-N line printer connected to the network.
The printer accepts data to print on port number 5100. The
host name of the printer is scrivener
.
Here is the text filter for the printer:
This section gives information on restricting printer usage. The LPD system lets you control who can access a printer, both locally or remotely, whether they can print multiple copies, how large their jobs can be, and how large the printer queues can get.
The LPD system makes it easy
for users to print multiple copies of a file. Users can
print jobs with lpr
(for example) and get five copies of each file in the job.
Whether this is a good thing is up to you.-#5
If you feel multiple copies cause unnecessary wear and
tear on your printers, you can disable the
-#
option to lpr(1) by adding the
sc
capability to the
/etc/printcap
file. When users submit
jobs with the -#
option, they will
see:
Note that if you have set up access to a printer
remotely (see section Printers
Installed on Remote Hosts), you need the
sc
capability on the remote
/etc/printcap
files as well, or else
users will still be able to submit multiple-copy jobs by
using another host.
Here is an example. This is the
/etc/printcap
file for the host
rose
. The printer
rattan
is quite hearty, so we will allow
multiple copies, but the laser
printer bamboo
is a bit more delicate, so
we will disable multiple copies by adding the
sc
capability:
/var/spool/lpd/rattan
:\
:lp=/dev/lpt0
:\
:if=/usr/local/libexec/if-simple
:
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
:sh:sd=/var/spool/lpd/bamboo
:sc:\
:lp=/dev/ttyu5
:ms#-parenb cs8 clocal crtscts:rw:\
:if=/usr/local/libexec/psif
:\
:df=/usr/local/libexec/psdf
:Now, we also need to add the sc
capability on the host orchid
's
/etc/printcap
(and while we are at it,
let us disable multiple copies for the printer
teak
):
/dev/lpt0
:sd=/var/spool/lpd/teak
:mx#0:sc:\
:if=/usr/local/libexec/ifhp
:\
:vf=/usr/local/libexec/vfhp
:\
:of=/usr/local/libexec/ofhp
:
rattan|line|diablo|lp|Diablo 630 Line Printer:\
:lp=:rm=rose:rp=rattan:sd=/var/spool/lpd/rattan
:
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
:lp=:rm=rose:rp=bamboo:sd=/var/spool/lpd/bamboo
:sc:By using the sc
capability, we
prevent the use of lpr
, but that still
does not prevent users from running lpr(1) multiple
times, or from submitting the same file multiple times in
one job like this:-#
%
lpr forsale.sign forsale.sign forsale.sign forsale.sign forsale.sign
There are many ways to prevent this abuse (including ignoring it) which you are free to explore.
You can control who can print to what printers by using
the UNIX® group mechanism and the rg
capability in /etc/printcap
. Just
place the users you want to have access to a printer in a
certain group, and then name that group in the
rg
capability.
If users outside the group (including
root
) try to print to the controlled
printer then they will be greeted with the following
message:
As with the sc
(suppress multiple
copies) capability, you need to specify
rg
on remote hosts that also have access
to your printers, if you feel it is appropriate (see section
Printers
Installed on Remote Hosts).
For example, we will let anyone access the printer
rattan
, but only those in group
artists
can use
bamboo
. Here is the familiar
/etc/printcap
for host
rose
:
/var/spool/lpd/rattan
:\
:lp=/dev/lpt0
:\
:if=/usr/local/libexec/if-simple
:
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
:sh:sd=/var/spool/lpd/bamboo
:sc:rg=artists:\
:lp=/dev/ttyu5
:ms#-parenb cs8 clocal crtscts:rw:\
:if=/usr/local/libexec/psif
:\
:df=/usr/local/libexec/psdf
:Let us leave the other example
/etc/printcap
file (for the host
orchid
) alone. Of course, anyone on
orchid
can print to
bamboo
. It
might be the case that we only allow certain logins on
orchid
anyway, and want them to have access
to the printer. Or not.
There can be only one restricted group per printer.
If you have many users accessing the printers, you probably need to put an upper limit on the sizes of the files users can submit to print. After all, there is only so much free space on the filesystem that houses the spooling directories, and you also need to make sure there is room for the jobs of other users.
LPD enables you to limit the
maximum byte size a file in a job can be with the
mx
capability. The units are in
BUFSIZ
blocks, which are 1024 bytes. If
you put a zero for this capability, there will be no limit
on file size; however, if no mx
capability is specified, then a default limit of 1000 blocks
will be used.
The limit applies to files in a job, and not the total job size.
LPD will not refuse a file that is larger than the limit you place on a printer. Instead, it will queue as much of the file up to the limit, which will then get printed. The rest will be discarded. Whether this is correct behavior is up for debate.
Let us add limits to our example printers
rattan
and bamboo
.
Since those artists
' PostScript®
files tend to be large, we will limit them to five
megabytes. We will put no limit on the plain text line
printer:
/var/spool/lpd/rattan
:\
:lp=/dev/lpt0
:\
:if=/usr/local/libexec/if-simple
:
#
# Limit of five megabytes:
#
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
:sh:sd=/var/spool/lpd/bamboo
:sc:rg=artists:mx#5000:\
:lp=/dev/ttyu5
:ms#-parenb cs8 clocal crtscts:rw:\
:if=/usr/local/libexec/psif
:\
:df=/usr/local/libexec/psdf
:Again, the limits apply to the local users only. If you
have set up access to your printers remotely, remote users
will not get those limits. You will need to specify the
mx
capability in the remote
/etc/printcap
files as well. See
section Printers Installed
on Remote Hosts for more information on remote
printing.
There is another specialized way to limit job sizes from remote printers; see section Restricting Jobs from Remote Hosts.
The LPD spooling system provides several ways to restrict print jobs submitted from remote hosts:
You can control from which remote hosts a local
LPD accepts requests with
the files /etc/hosts.equiv
and
/etc/hosts.lpd
.
LPD checks to see if an
incoming request is from a host listed in either one
of these files. If not,
LPD refuses the
request.
The format of these files is simple: one host name
per line. Note that the file
/etc/hosts.equiv
is also used by
the ruserok(3) protocol, and affects programs
like rsh(1) and rcp(1), so be
careful.
For example, here is the
/etc/hosts.lpd
file on the host
rose
:
This means rose
will accept
requests from the hosts orchid
,
violet
, and madrigal.fishbaum.de
. If any
other host tries to access rose
's
LPD, the job will be
refused.
You can control how much free space there needs to
remain on the filesystem where a spooling directory
resides. Make a file called
minfree
in the spooling
directory for the local printer. Insert in that file
a number representing how many disk blocks (512 bytes)
of free space there has to be for a remote job to be
accepted.
This lets you insure that remote users will not
fill your filesystem. You can also use it to give a
certain priority to local users: they will be able to
queue jobs long after the free disk space has fallen
below the amount specified in the
minfree
file.
For example, let us add a
minfree
file for the printer
bamboo
. We examine
/etc/printcap
to find the
spooling directory for this printer; here is
bamboo
's entry:
/var/spool/lpd/bamboo
:sc:rg=artists:mx#5000:\
:lp=/dev/ttyu5
:ms#-parenb cs8 clocal crtscts:rw:mx#5000:\
:if=/usr/local/libexec/psif
:\
:df=/usr/local/libexec/psdf
:The spooling directory is given in the
sd
capability. We will make three
megabytes (which is 6144 disk blocks) the amount of
free disk space that must exist on the filesystem for
LPD to accept remote
jobs:
#
echo 6144 > /var/spool/lpd/bamboo/minfree
You can control which remote users can print to
local printers by specifying the rs
capability in /etc/printcap
.
When rs
appears in the entry for a
locally-attached printer,
LPD will accept jobs from
remote hosts if the user
submitting the job also has an account of the same
login name on the local host. Otherwise,
LPD refuses the job.
This capability is particularly useful in an
environment where there are (for example) different
departments sharing a network, and some users
transcend departmental boundaries. By giving them
accounts on your systems, they can use your printers
from their own departmental systems. If you would
rather allow them to use only
your printers and not your computer resources, you can
give them “token” accounts, with no home
directory and a useless shell like
/usr/bin/false
.
So, you need to charge for printouts. And why not? Paper and ink cost money. And then there are maintenance costs—printers are loaded with moving parts and tend to break down. You have examined your printers, usage patterns, and maintenance fees and have come up with a per-page (or per-foot, per-meter, or per-whatever) cost. Now, how do you actually start accounting for printouts?
Well, the bad news is the LPD spooling system does not provide much help in this department. Accounting is highly dependent on the kind of printer in use, the formats being printed, and your equirements in charging for printer usage.
To implement accounting, you have to modify a printer's text filter (to charge for plain text jobs) and the conversion filters (to charge for other file formats), to count pages or query the printer for pages printed. You cannot get away with using the simple output filter, since it cannot do accounting. See section Filters.
Generally, there are two ways to do accounting:
Periodic accounting is the more common way, possibly because it is easier. Whenever someone prints a job, the filter logs the user, host, and number of pages to an accounting file. Every month, semester, year, or whatever time period you prefer, you collect the accounting files for the various printers, tally up the pages printed by users, and charge for usage. Then you truncate all the logging files, starting with a clean slate for the next period.
Timely accounting is less common, probably because it is more difficult. This method has the filters charge users for printouts as soon as they use the printers. Like disk quotas, the accounting is immediate. You can prevent users from printing when their account goes in the red, and might provide a way for users to check and adjust their “print quotas”. But this method requires some database code to track users and their quotas.
The LPD spooling system supports both methods easily: since you have to provide the filters (well, most of the time), you also have to provide the accounting code. But there is a bright side: you have enormous flexibility in your accounting methods. For example, you choose whether to use periodic or timely accounting. You choose what information to log: user names, host names, job types, pages printed, square footage of paper used, how long the job took to print, and so forth. And you do so by modifying the filters to save this information.
FreeBSD comes with two programs that can get you set up
with simple periodic accounting right away. They are the
text filter lpf
, described in section
lpf: a Text
Filter, and pac(8), a program to gather and
total entries from printer accounting files.
As mentioned in the section on filters (Filters),
LPD starts the text and the
conversion filters with the name of the accounting file to
use on the filter command line. The filters can use this
argument to know where to write an accounting file entry.
The name of this file comes from the af
capability in /etc/printcap
, and if not
specified as an absolute path, is relative to the spooling
directory.
LPD starts
lpf
with page width and length arguments
(from the pw
and pl
capabilities). The lpf
filter uses these
arguments to determine how much paper will be used. After
sending the file to the printer, it then writes an
accounting entry in the accounting file. The entries look
like this:
You should use a separate accounting file for each
printer, as lpf
has no file locking logic
built into it, and two lpf
s might corrupt
each other's entries if they were to write to the same file
at the same time. An easy way to insure a separate
accounting file for each printer is to use
af=acct
in
/etc/printcap
. Then, each accounting
file will be in the spooling directory for a printer, in a
file named acct
.
When you are ready to charge users for printouts, run
the pac(8) program. Just change to the spooling
directory for the printer you want to collect on and type
pac
. You will get a dollar-centric
summary like the following:
These are the arguments pac(8) expects:
-Pprinter
Which printer
to
summarize. This option works only if there is an
absolute path in the af
capability
in /etc/printcap
.
-c
Sort the output by cost instead of alphabetically by user name.
-m
Ignore host name in the accounting files. With
this option, user smith
on host
alpha
is the same user
smith
on host
gamma
. Without, they are different
users.
-pprice
Compute charges with
price
dollars per page or
per foot instead of the price from the
pc
capability in
/etc/printcap
, or two cents (the
default). You can specify
price
as a floating point
number.
-r
Reverse the sort order.
-s
Make an accounting summary file and truncate the accounting file.
name
…
Print accounting information for the given user
names
only.
In the default summary that pac(8) produces, you
see the number of pages printed by each user from various
hosts. If, at your site, host does not matter (because
users can use any host), run pac
, to produce the following
summary:-m
To compute the dollar amount due,
pac(8) uses the pc
capability in the
/etc/printcap
file (default of 200, or
2 cents per page). Specify, in hundredths of cents, the
price per page or per foot you want to charge for printouts
in this capability. You can override this value when you
run pac(8) with the -p
option. The
units for the -p
option are in dollars,
though, not hundredths of cents. For example,
#
pac -p1.50
makes each page cost one dollar and fifty cents. You can really rake in the profits by using this option.
Finally, running pac
will
save the summary information in a summary accounting file,
which is named the same as the printer's accounting file,
but with -s
_sum
appended to the name. It
then truncates the accounting file. When you run
pac(8) again, it rereads the summary file to get
starting totals, then adds information from the regular
accounting file.
In order to perform even remotely accurate accounting, you need to be able to determine how much paper a job uses. This is the essential problem of printer accounting.
For plain text jobs, the problem is not that hard to solve: you count how many lines are in a job and compare it to how many lines per page your printer supports. Do not forget to take into account backspaces in the file which overprint lines, or long logical lines that wrap onto one or more additional physical lines.
The text filter lpf
(introduced in
lpf: a Text
Filter) takes into account these things when it
does accounting. If you are writing a text filter which
needs to do accounting, you might want to examine
lpf
's source code.
How do you handle other file formats, though?
Well, for DVI-to-LaserJet or DVI-to-PostScript®
conversion, you can have your filter parse the diagnostic
output of dvilj
or
dvips
and look to see how many pages were
converted. You might be able to do similar things with
other file formats and conversion programs.
But these methods suffer from the fact that the printer may not actually print all those pages. For example, it could jam, run out of toner, or explode—and the user would still get charged.
So, what can you do?
There is only one sure way to do accurate accounting. Get a printer that can tell you how much paper it uses, and attach it via a serial line or a network connection. Nearly all PostScript® printers support this notion. Other makes and models do as well (networked Imagen laser printers, for example). Modify the filters for these printers to get the page usage after they print each job and have them log accounting information based on that value only. There is no line counting nor error-prone file examination required.
Of course, you can always be generous and make all printouts free.
All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/
Questions that are not answered by the
documentation may be
sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.