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 on each of your printers.
LPD expects every printer to be able to print plain text by default. This presents a problem for PostScript® (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 -t
to print troff data, or
lpr -d
to print TeX DVI data, or lpr
-v
to print raster image data, and so forth. I
recommend reading this section.
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 -t
, LPD would
start the troff filter, listed
in the 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] -wwidth
-llength
-iindent
-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
-i
, default 0
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
-xpixel-width
-ypixel-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 my experience, output filters are rarely used. Section Output Filters describe them. There are only two arguments to an output filter:
filter-name
-wwidth
-llength
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
fetch, build and install it yourself, of course. 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
:
:if=/usr/local/libexec/psif:
You should also specify the rw
capability;
that tells LPD to open the printer in
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:
#!/bin/sh # # psif - Print PostScript or plain text on a PostScript printer # Script version; NOT the version that comes with lprps # Installed in /usr/local/libexec/psif # IFS="" read -r first_line first_two_chars=`expr "$first_line" : '\(..\)'` if [ "$first_two_chars" = "%!" ]; then # # PostScript job, print it. # echo "$first_line" && cat && printf "\004" && exit 0 exit 2 else # # Plain text, convert it, then print it. # ( echo "$first_line"; cat ) | /usr/local/bin/textps && printf "\004" && exit 0 exit 2 fi
In the above script, textps
is a program we
installed separately to convert plain text to PostScript®. You can
use any text-to-PostScript® program you wish. The FreeBSD Ports
Collection (see The Ports Collection)
includes a full featured text-to-PostScript® program called
a2ps
that you might want to investigate.
PostScript® is the de facto standard for high quality typesetting and printing. PostScript® is, however, an expensive standard. Thankfully, Aladdin Enterprises has a free PostScript® work-alike called Ghostscript that runs with FreeBSD. Ghostscript can read most PostScript® files and can render their pages onto a variety of devices, including many brands of non-PostScript printers. By installing Ghostscript and using a special text filter for your printer, you can make your non PostScript® printer act like a real PostScript® printer.
Ghostscript is in the FreeBSD Ports Collection, if you would like to install it from there. You can fetch, build, and install it quite easily yourself, as well.
To simulate PostScript®, we have the text filter detect if it is printing a PostScript® file. If it is not, then the filter will pass the file directly to the printer; otherwise, it will use Ghostscript to first convert the file into a format the printer will understand.
Here is an example: the following script is a text filter
for Hewlett Packard DeskJet 500 printers. For other printers,
substitute the -sDEVICE
argument to the
gs
(Ghostscript) command. (Type gs
-h
to get a list of devices the current installation of
Ghostscript supports.)
#!/bin/sh # # ifhp - Print Ghostscript-simulated PostScript on a DeskJet 500 # Installed in /usr/local/libexec/ifhp # # Treat LF as CR+LF (to avoid the "staircase effect" on HP/PCL # printers): # printf "\033&k2G" || exit 2 # # Read first two characters of the file # IFS="" read -r first_line first_two_chars=`expr "$first_line" : '\(..\)'` if [ "$first_two_chars" = "%!" ]; then # # It is PostScript; use Ghostscript to scan-convert and print it. # /usr/local/bin/gs -dSAFER -dNOPAUSE -q -sDEVICE=djet500 \ -sOutputFile=- - && exit 0 else # # Plain text or HP/PCL, so just print it directly; print a form feed # at the end to eject the last page. # echo "$first_line" && cat && printf "\033&l0H" && exit 0 fi exit 2
Finally, you need to notify LPD of
the filter via the if
capability:
:if=/usr/local/libexec/ifhp:
That is it. You can type lpr plain.text
and
lpr whatever.ps
and both should print
successfully.
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 -d
means the
printer needs a 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 -g
mean „print Printerleaf
files.”
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
.
# # /etc/printcap for host rose - added df filter for bamboo # rattan|line|diablo|lp|Diablo 630 Line Printer:\ :sh:sd=/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/ttyd5: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:
#!/bin/sh # # psdf - DVI to PostScript printer filter # Installed in /usr/local/libexec/psdf # # Invoked by lpd when user runs lpr -d # exec /usr/local/bin/dvips -f | /usr/local/libexec/lprps "$@"
This script runs dvips
in filter mode (the
-f
argument) on standard input, which is the job
to print. It then starts the PostScript® printer filter
lprps
(see section Accommodating Plain
Text Jobs on PostScript® Printers) with the arguments
LPD
passed to this script. lprps
will use those
arguments to account for the pages printed.
Since there is no fixed set of steps to install conversion filters, let me instead provide more examples. Use these as guidance to making your own filters. Use them directly, if appropriate.
This example script is a raster (well, GIF file, actually) conversion filter for a Hewlett Packard LaserJet III-Si printer:
#!/bin/sh # # hpvf - Convert GIF files into HP/PCL, then print # Installed in /usr/local/libexec/hpvf PATH=/usr/X11R6/bin:$PATH; export PATH giftopnm | ppmtopgm | pgmtopbm | pbmtolj -resolution 300 \ && exit 0 \ || exit 2
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:
# # /etc/printcap for host orchid # teak|hp|laserjet|Hewlett Packard LaserJet 3Si:\ :lp=/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
:
#!/bin/sh # # pstf - Convert groff's troff data into PS, then print. # Installed in /usr/local/libexec/pstf # exec grops | /usr/local/libexec/lprps "$@"
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:
#!/bin/sh # # pstf - Convert groff's troff data into PS, then print. # Installed in /usr/local/libexec/pstf # exec grops
That is it. Here is the entry we need to add to
/etc/printcap
to enable the filter:
:tf=/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
:
#!/bin/sh # # hprf - FORTRAN text filter for LaserJet 3si: # Installed in /usr/local/libexec/hprf # printf "\033&k2G" && fpr && printf "\033&l0H" && exit 0 exit 2
And we will add this line to the
/etc/printcap
for the printer
teak
to enable this filter:
:rf=/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:
:df=/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: dvi2xx
is the name of the package.
Installing this package gives us the program we need,
dvilj2p
, which converts DVI into LaserJet IIp,
LaserJet III, and LaserJet 2000 compatible codes.
dvilj2p
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:
#!/bin/sh # # hpdf - Print DVI data on HP/PCL printer # Installed in /usr/local/libexec/hpdf PATH=/usr/local/bin:$PATH; export PATH # # Define a function to clean up our temporary files. These exist # in the current directory, which will be the spooling directory # for the printer. # cleanup() { rm -f hpdf$$.dvi } # # Define a function to handle fatal errors: print the given message # and exit 2. Exiting with 2 tells LPD to do not try to reprint the # job. # fatal() { echo "$@" 1>&2 cleanup exit 2 } # # If user removes the job, LPD will send SIGINT, so trap SIGINT # (and a few other signals) to clean up after ourselves. # trap cleanup 1 2 15 # # Make sure we are not colliding with any existing files. # cleanup # # Link the DVI input file to standard input (the file to print). # ln -s /dev/fd/0 hpdf$$.dvi || fatal "Cannot symlink /dev/fd/0" # # Make LF = CR+LF # printf "\033&k2G" || fatal "Cannot initialize printer" # # Convert and print. Return value from dvilj2p does not seem to be # reliable, so we ignore it. # dvilj2p -M1 -q -e- dfhp$$.dvi # # Clean up and exit # cleanup exit 0
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
. It can
detect plain text, PostScript®, and DVI 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
-i
), allow literal characters to pass (job submitted
with lpr -l
), adjust the printing position for
backspaces and tabs in the job, and account for pages printed. It
can also act like an output filter.
lpf
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:
#!/bin/sh # # hpof - Output filter for Hewlett Packard PCL-compatible printers # Installed in /usr/local/libexec/hpof printf "\033&k2G" || exit 2 exec /usr/libexec/lpr/lpf
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:
# # /etc/printcap for host orchid # teak|hp|laserjet|Hewlett Packard LaserJet 3Si:\ :lp=/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 -h
; see the Header Page Options section for
more lpr(1) options.
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
):
k ll ll k l l k l l k k eeee l l y y k k e e l l y y k k eeeeee l l y y kk k e l l y y k k e e l l y yy k k eeee lll lll yyy y y y y yyyy ll t l i t l oooo u u ttttt l ii n nnn eeee o o u u t l i nn n e e o o u u t l i n n eeeeee o o u u t l i n n e o o u uu t t l i n n e e oooo uuu u tt lll iii n n eeee r rrr oooo ssss eeee rr r o o s s e e r o o ss eeeeee r o o ss e r o o s s e e r oooo ssss eeee Job: outline Date: Sun Sep 17 11:04:58 1995
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:
rose:kelly Job: outline Date: Sun Sep 17 11:07:51 1995
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
„add one page” to the text filter or any of the
conversion filters (which do have user and host information) since
users can suppress header pages with lpr -h
.
They could still be charged for header pages they did not print.
Basically, lpr -h
will be the preferred option of
environmentally-minded users, but you cannot offer any incentive to
use it.
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 -h
, they will still get
them and be charged for them since LPD
does not pass any knowledge
of the -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:
#!/bin/sh # # make-ps-header - make a PostScript header page on stdout # Installed in /usr/local/libexec/make-ps-header # # # These are PostScript units (72 to the inch). Modify for A4 or # whatever size paper you are using: # page_width=612 page_height=792 border=72 # # Check arguments # if [ $# -ne 3 ]; then echo "Usage: `basename $0` <user> <host> <job>" 1>&2 exit 1 fi # # Save these, mostly for readability in the PostScript, below. # user=$1 host=$2 job=$3 date=`date` # # Send the PostScript code to stdout. # exec cat <<EOF %!PS % % Make sure we do not interfere with user's job that will follow % save % % Make a thick, unpleasant border around the edge of the paper. % $border $border moveto $page_width $border 2 mul sub 0 rlineto 0 $page_height $border 2 mul sub rlineto currentscreen 3 -1 roll pop 100 3 1 roll setscreen $border 2 mul $page_width sub 0 rlineto closepath 0.8 setgray 10 setlinewidth stroke 0 setgray % % Display user's login name, nice and large and prominent % /Helvetica-Bold findfont 64 scalefont setfont $page_width ($user) stringwidth pop sub 2 div $page_height 200 sub moveto ($user) show % % Now show the boring particulars % /Helvetica findfont 14 scalefont setfont /y 200 def [ (Job:) (Host:) (Date:) ] { 200 y moveto show /y y 18 sub def } forall /Helvetica-Bold findfont 14 scalefont setfont /y 200 def [ ($job) ($host) ($date) ] { 270 y moveto show /y y 18 sub def } forall % % That is it % restore showpage EOF
Now, each of the conversion filters and the text filter can call this script to first generate the header page, and then print the user's job. Here is the DVI conversion filter from earlier in this document, modified to make a header page:
#!/bin/sh # # psdf - DVI to PostScript printer filter # Installed in /usr/local/libexec/psdf # # Invoked by lpd when user runs lpr -d # orig_args="$@" fail() { echo "$@" 1>&2 exit 2 } while getopts "x:y:n:h:" option; do case $option in x|y) ;; # Ignore n) login=$OPTARG ;; h) host=$OPTARG ;; *) echo "LPD started `basename $0` wrong." 1>&2 exit 2 ;; esac done [ "$login" ] || fail "No login name" [ "$host" ] || fail "No host name" ( /usr/local/libexec/make-ps-header $login $host "DVI File" /usr/local/bin/dvips -f ) | eval /usr/local/libexec/lprps $orig_args
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 -h
, 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.
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 (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 Printers).
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
:
# # /etc/printcap for host orchid - added (remote) printers on rose # # # teak is local; it is connected directly to orchid: # teak|hp|laserjet|Hewlett Packard LaserJet 3Si:\ :lp=/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.).
#!/usr/bin/perl # # netprint - Text filter for printer attached to network # Installed in /usr/local/libexec/netprint # $#ARGV eq 1 || die "Usage: $0 <printer-hostname> <port-number>"; $printer_host = $ARGV[0]; $printer_port = $ARGV[1]; require 'sys/socket.ph'; ($ignore, $ignore, $protocol) = getprotobyname('tcp'); ($ignore, $ignore, $ignore, $ignore, $address) = gethostbyname($printer_host); $sockaddr = pack('S n a4 x8', &AF_INET, $printer_port, $address); socket(PRINTER, &PF_INET, &SOCK_STREAM, $protocol) || die "Can't create TCP/IP stream socket: $!"; connect(PRINTER, $sockaddr) || die "Can't contact $printer_host: $!"; while (<STDIN>) { print PRINTER; } exit 0;
We can then use this script in various filters. Suppose we had a Diablo 750-N line printer connected to the network. The printer accepts data to print on port number 5100. The host name of the printer is scrivener. Here is the text filter for the printer:
#!/bin/sh # # diablo-if-net - Text filter for Diablo printer `scrivener' listening # on port 5100. Installed in /usr/local/libexec/diablo-if-net # exec /usr/libexec/lpr/lpf "$@" | /usr/local/libexec/netprint scrivener 5100
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 -#5
(for example) and get five copies of each file in the job. Whether
this is a good thing is up to you.
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:
lpr: multiple copies are not allowed
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:
# # /etc/printcap for host rose - restrict multiple copies on bamboo # rattan|line|diablo|lp|Diablo 630 Line Printer:\ :sh:sd=/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/ttyd5: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
):
# # /etc/printcap for host orchid - no multiple copies for local # printer teak or remote printer bamboo teak|hp|laserjet|Hewlett Packard LaserJet 3Si:\ :lp=/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.
Users outside the group (including root
)
will be greeted with
lpr: Not a member of the restricted group
if they try to print to the controlled printer.
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
:
# # /etc/printcap for host rose - restricted group for bamboo # rattan|line|diablo|lp|Diablo 630 Line Printer:\ :sh:sd=/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/ttyd5: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:
# # /etc/printcap for host rose # # # No limit on job size: # rattan|line|diablo|lp|Diablo 630 Line Printer:\ :sh:mx#0:sd=/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/ttyd5: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 Printers.
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
:
orchid violet madrigal.fishbaum.de
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:
bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\ :sh:sd=/var/spool/lpd/bamboo:sc:rg=artists:mx#5000:\ :lp=/dev/ttyd5: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 requirements 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). lpf
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:
2.00 rose:andy 3.00 rose:kelly 3.00 orchid:mary 5.00 orchid:mary 2.00 orchid:zhang
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:
Login pages/feet runs price orchid:kelly 5.00 1 $ 0.10 orchid:mary 31.00 3 $ 0.62 orchid:zhang 9.00 1 $ 0.18 rose:andy 2.00 1 $ 0.04 rose:kelly 177.00 104 $ 3.54 rose:mary 87.00 32 $ 1.74 rose:root 26.00 12 $ 0.52 total 337.00 154 $ 6.74
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 -m
, to produce the following
summary:
Login pages/feet runs price andy 2.00 1 $ 0.04 kelly 182.00 105 $ 3.64 mary 118.00 35 $ 2.36 root 26.00 12 $ 0.52 zhang 9.00 1 $ 0.18 total 337.00 154 $ 6.74
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 -s
will save the summary
information in a summary accounting file, which is named the same as
the printer's accounting file, but with _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.
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sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.