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Managing the UNIX Print Queue

Once the print jobs coming in from clients are received on the FreeBSD system and placed in the print spool, they are metered out at a slower rate to the various printers. If traffic activity is light and few print jobs get sent through, the administrator can probably ignore the print queue as long as it continues to work. However, a busy network printer running at an optimal rate of speed usually has a backlog of unprinted jobs in the queue waiting for print time. To keep all users happy and to provide for the occasional rush print job, the UNIX LPD/LPR printing system has several administration commands, which are described here.

Viewing the Queue

On busy printers, and to troubleshoot stopped printers, users sometimes need to view the print jobs in the queue. Administrators also must view the queue to see what jobs may need to be expedited. This can be done from the workstation that remotely submitted the job if the LPR client has the ability to do it. The Windows 3.1 LPR client discussed earlier has this capability. Unfortunately, many LPR clients don't, which means that the administrator must Telnet into the UNIX machine that the print queues are on and view them there.

The UNIX shell command used to view the queue is the lpq command. It is frequently run as lpq -a, which shows jobs in all queues. The following is a sample output of the command.

# lpq -a
nec-raw:
Rank Owner Job Files                          Total Size
1st  tedm  19  C:/WLPRSPL/SPOOL/~LP00018.TMP  105221 bytes
2nd  tedm  20  C:/WLPRSPL/SPOOL/~LP00019.TMP  13488 bytes
3rd  root  3   hosts                          1220 bytes
4th  tedm  1   Printer Test Page              765 bytes
5th  tedm  2   Microsoft Word - CHAPTE10.DOC  15411 bytes
#

The first two jobs and the last two jobs came from remote clients; the third came from the command prompt.

Removing Print Jobs

Deleting unwanted print jobs that haven't yet printed from the queue can be done by the remote workstations that submitted the job if their LPR implementations have the necessary commands. The Windows 3.1 LPR client I detailed earlier has this capability. Many LPR clients don't, however, which means that the administrator must Telnet into the UNIX machine that the print queues are on and delete the jobs there.

The administrator can delete any print jobs from any queues by running the lprm command followed by the specified print queue and the job number. Below is a sample output of the command.

# lprm -P nec-raw 19
dfA019tedmitte dequeued
cfA019dostest dequeued
# lprm -P nec-raw 3
dfA003toybox.placo.com dequeued
cfA003toybox.placo.com dequeued
#

The lprm command is also used under UNIX to delete remote print jobs.

Advanced Management

The administrator logged into the FreeBSD system as the root user can also perform several other operations that ordinary users cannot. These include turning the queues on and off and moving print jobs within the print queues. The command used to do this is the lpc command.

lpc has two modes of operation. In the first mode, the command is run by itself, which puts the administrator into an lpc prompt. Some general help is available for the commands, such as the following sample output.

# lpc
lpc> help
Commands may be abbreviated. Commands are
abort enable disable help restart status topq ?
clean exit down quit start stop up
lpc> help disable
disable  turn a spooling queue off
lpc> help status
status   show status of daemon and queue
lpc> exit
#

In the second mode of operation, the lpc command is just run by itself, followed by the command and the print queue name. Following is a sample output.

# lpc disable lp
lp:
    queuing disabled
#

Under FreeBSD, there is no command that specifically allows the administrator to move jobs from one queue to another. This can be done, however, by changing into the raw queue directory and then rerunning the lpr command. Following is a sample run showing three print jobs moved from a dysfunctional queue to a good one.

# lpq -a
lp:
Warning: lp is down: printing disabled
printing disabled
Rank Owner  Job Files         Total Size
1st  root   51  hosts         1220 bytes
2nd  root   52  services        60767 bytes
3rd  root   53  printcap        2383 bytes
# cd /var/spool/output/lpd
# ls
.seq          cfA053toybox.placo.com dfA053toybox.placo.com
cfA051toybox.placo.com dfA051toybox.placo.com lock
cfA052toybox.placo.com dfA052toybox.placo.com status
# lpr -P nec-raw dfA051toybox.placo.com
# lpr -P nec-raw dfA052toybox.placo.com
# lpr -P nec-raw dfA053toybox.placo.com
# lprm -P lp -
# lpq -a
nec-raw:
Warning: nec-raw is down: printing disabled
Warning: no daemon present
Rank Owner   Job  Files          Total Size
1st  root    5   dfA051toybox.placo.com  1220 bytes
2nd  root    6   dfA052toybox.placo.com  60767 bytes
3rd  root    7   dfA053toybox.placo.com  2383 bytes
#

Note - Moving jobs from queue to queue is feasible only when all printers are similar, as when all printers support PostScript.


Remote Management

Just as the root user can manipulate remotely submitted jobs in the print queue, print jobs can be remotely managed by regular users with the LPR clients that created them. Unfortunately, some LPR clients, such as Win95, don't have enough programming to be able to do this. Others, like the Win31 client, can manipulate the print jobs remotely.

FreeBSD offers some level of protection against inadvertent deletion of print jobs from remote hosts by restricting manipulation of a job to the same host that originated it. Even if the owner of the job matches a local user account on the server, for an ordinary user to delete remotely submitted print jobs, the request still must come from the remote host.

Advanced Printing Topics

The FreeBSD UNIX LPR/LPD printing system is very flexible and, with the addition of filters, can be adapted to very unusual printing environments. To enhance this flexibility several useful printing utilities are supplied on the FreeBSD CD-ROM, which the administrator might wish to install.

Ghostscript

The Ghostscript program, invoked as /usr/local/bin/gs, is one of the most useful printing utilities that have been developed for the free software community. Ghostscript reads incoming PostScript data (or Adobe PDF files), interprets it, and outputs it as a raster image. This can be displayed on screen, for example, with the GhostView program under the X Window System, or printed on most graphics printers, such as Epson dot-matrix, HP DeskJet, or HP LaserJet. In effect, it is a way of adding PostScript printing capability to a printer that doesn't have PostScript firmware code. Ghostscript has been ported to numerous operating systems, including Windows.

The Ghostscript home page is located at http://www.cs.wisc.edu/~ghost/ and contains the most current version of the program. A prebuilt FreeBSD binary of Ghostscript is located in the Packages section of the FreeBSD CD-ROM. This can be installed on the FreeBSD system by selecting the package from the prepackaged software list that is accessed through the /stand/sysinstall installation program. Many packaged programs on the CD depend on Ghostscript, and so it may already be installed.

Installation of the packaged version of Ghostscript is recommended in the FreeBSD Ports Section because it has been tested with the other packages that require it. The package creates a directory containing some documentation files in /usr/local/share/"ghostscript/X.XX/doc. Unfortunately, because of the packaging process on the FreeBSD CD-ROM not all the useful installation files are copied into this location. So, if the package is version 5.03 (for example), the administrator will also want to get the file ftp://ftp.cs.wisc.edu/ghost/aladdin/gs503/ghostscript-5.03.tar.gz, and unzip and untar it into a temporary directory.

Extracting the archive file creates a directory structure under the gs5.03 subdirectory. To install Ghostscript in the /etc/printcap file, read the gs5.03/devs.mak file to determine which printer driver definition works with your printer, and then use the instructions in Exhibit 8.5.

Exhibit 8.5 Installing Ghostscript in the /etc/printcap file

  1. Change to the root user with su.

  2. In the gs5.03 directory, copy the lprsetup.sh, unix-lpr.txt, and unix-lpr.sh files to /usr/local/share/ghostscript/5.03.

  3. Change to the /usr/local/share/ghostscript/5.03 directory. Edit lprsetup.sh with a text editor such as vi.

  4. Modify the DEVICES= entries to list your selected printer driver definitions per the instructions in unix-lpr.txt.

  5. Modify the PRINTERDEV= to /dev/lpt0, the GSDIR= to /usr/local/share/ ghostscript, and the SPOOLDIR= to /var/spool/output. Save the file.

  6. Edit the unix-lpr.sh file and change the PSFILTERPATH= to /usr/local/share/ ghostscript.

  7. If the printer that you defined in the lprsetup.sh file is a monochrome printer, remove the "-dBitsPerPixel=${bpp}" and "$colorspec" entries on the gs invocation line and save the file. Otherwise, if it is a color definition, leave them in. For example, the following line is for a monochrome LaserJet.

    ") | gs -q -dNOPAUSE -sDEVICE=${device} \"

    Don't remove anything else. Exit the editor, and save the unix-lpr.sh file.

  8. Copy the unix-lpr.sh file to the parent directory, /usr/local/share/ ghostscript, and set the execute bit on it.

  9. Set the execute bit on lprsetup.sh with chmod and run the file by typing ./lprsetup.sh.

  10. Follow the instructions for creating the Spool directories. If you will be using accounting and a separate log file, run the touch command to create the empty files per directions in script output.

  11. The sample /etc/printcap is located in the current directory; the filename is printcap. insert. Use this as a template to modify the /etc/printcap file. A sample /etc/printcap file for a LaserJet 3 follows:

    #
    #
    ljet3.raw|Raw output device ljet3 for Ghostscript:
       :rm=big.army.mil:rp=sherman:sd=/var/spool/output/ljet3/raw:
       :mx#0:sf:sh:rs:
    #
    ljet3|Ghostscript device ljet3 (output to ljet3.raw):
       :lp=/dev/null:sd=/var/spool/output/ljet3:
       :lf=/var/log/lpd-errs:mx#0:sf:sh:rs:
       :if=/usr/local/share/ghostscript/filt/indirect/ljet3/gsif:
       :af=/var/spool/output/ljet3/acct:
    #
    #

A2ps Filter

Another handy utility is the a2ps, short for ASCII-to-PostScript. This program takes an incoming ASCII datastream and converts it to PostScript. It can also print multiple pages on a single sheet of paper by shrinking them down. It is a useful tool for a printer that cannot interpret ASCII, such as a PostScript-only printer.

a2ps is not installed in the FreeBSD system by default; it is located in the ports section /usr/ports/print/a2ps43. A prepackaged binary can be installed with /stand/sysinstall, but I have had problems with that port. It is best to install it by running make in the a2ps43 Ports directory, as follows.

/etc/printcap
#
lp|local l-ine printer with output dumped through a2ps for raw listings:
   :lp=/-dev/lpt0:sd=/var/spool/output/lpd:lf=/var/log/lpd- errs:sh:mx#0:
   :if=/usr/local/libexec/ascii2postscript:
#
/usr/local/libexec/ascii2postscript
#!/bin/sh
#
# Simple filter that converts ASCII to PostScript for basic stuff like
# directory listings.
#
/usr/local/bin/a2ps && exit 0
exit 2

Read the system manual page for a2ps to see the options available with this program, and remember to set the filter script ascii2postscript all-executable.

Miscellaneous

The large number of other printing utilities cannot be covered here. Some add features such as automatic job type sensing; others handle bidirectional communication between the server and the printer. There are also a few other experimental LPR printing replacement systems. Commands such as Ghostscript and a2ps can also be used in pipes that create pretty output on an ordinary impact printer.

One last hint: The system manual pages can be printed with the -t option, which turns their ordinary ASCII output to beautifully formatted PostScript. Try the man -t man command, and send the output through Ghostscript or a PostScript printer for easier-to-read manual pages.

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