Editing System V printing system

{{Short description|Printing subsystem of UNIX System V}}
The [[Printer (computing)|printing]] subsystem of [[UNIX System V]] is one of several standardized systems for printing on Unix, and is typical of commercial System V-based Unix versions such as [[Solaris (operating system)|Solaris]] and [[SCO OpenServer]]. A system running this print architecture could traditionally be identified by the use of the user command {{mono|lp}} as the primary interface to the print system, as opposed to the [[Berkeley Software Distribution|BSD]] [[Line Printer Daemon protocol|{{mono|lpr}}]] command (though some systems provide {{mono|lpr}} as an alias to {{mono|lp}}).

Typical user commands available to the System V printing system are:

*{{mono|lp}}: the user command to print a document
*{{mono|lpstat}}: shows the current print queue
*{{mono|cancel}}: deletes a job from the print queue
*{{mono|lpadmin}}: a system administration command that configures the print system
*{{mono|lpmove}}: a system administration command that moves jobs between print queues

==History==
In the Unix programming model, [[device file]]s are special files that act as access points to peripheral devices such as printers.  For example, the first [[line printer]] on a Unix system might be represented by a file {{mono|lp1}} in the device ({{mono|/dev}}) directory, ''i.e.'', {{mono|/dev/lp1}}.  Using the file metaphor, a document could by printed by "copying" the file onto the device: {{mono|cp document /dev/lp1}}.  While this worked well enough for the case where there was one printer per user, this model did not scale out well to [[Time-sharing|multiple users]] having to share one printer.<ref name=Kofler1997/>  The solution was to create a queue (or "spool") of documents to be printed and use a [[Daemon (computing)|daemon]] (system process) to manage this queue and send the documents to the printer in the order in which they arrived.

Such a system, with an {{mono|lp}} command to send documents to the queue, was first introduced in 1973 in [[Research Unix|Version 4]] of Unix.{{r|Arthur1986}} By the release of [[UNIX System V#SVR4|System V Release 4]], the suite of utilities had grown to include commands for canceling print jobs, moving jobs among queues, enabling and disabling queues, enabling and disabling a job scheduler daemon, and status reports of the print system.{{r|Nemeth1985}} The {{mono|lp}} command handled queue documents to be printed{{r|Nemeth1985}} and had over 20 different options that controlled the appearance of the document and its place in the queue,{{r|Rosen1990}} and even handled email notification of the user once the document had finished printing.{{r|Arthur1986}} The command returned a "job id" which could be used by the ''cancel'' or ''lpstat'' commands to remove the job from the queue or check on its progress, respectively.{{r|Sobell1985}} While the system was considered to be quite complex to set up and administer, most uses were expected to only use these three commands.{{r|Rosen1990}}

With its distribution in the influential AT&T Unix System V, the interface if not the implementation became the standard for users' control over printers.  The {{mono|lp}} command was included as a requirement in the [[POSIX#POSIX.2|POSIX]].2 standard,<ref name=Gardner1994/> and a command by that name appeared in the subsequent lpr, [[LPRng]] and [[CUPS]] printing systems.  (In SVR4 derivates like [[SCO OpenServer|SCO UNIX]], the {{mono|lp}} command was simply an alias for the {{mono|lpr}} command used by the BSD-based {{mono|lpr}} system.<ref name=Cutler1994/>)

As late as 1996, ''Running [[Linux]]'' stated "The Linux printing software consists of the UNIX standard ''lp'' and ''lpr'' software,"<ref name=Welsh1995/> but by 1999 support for ''lp'' was waning and the third edition simply stated "The ''lpr'' command prints a document on Linux."<ref name=Welsh1999/>  By 2003, a survey of the [[Debian]], [[Mandriva Linux|Mandrake]], [[Red Hat Linux|Red Hat]], [[Slackware]] and [[SUSE Linux|SuSE]] distributions showed that all of them were running some combination of lpr, LPRng and CUPS.<ref name=Smith2003/>

The original System V printing system remains proprietary; however, the Solaris print system, heavily modified from the original, has been released as [[open source software]] as part of the [[OpenSolaris]] project. The [[Common Unix Printing System]] emulates both System V and Berkeley print architectures on the interface level, though its internal architecture is different from both.

==Criticism==
In his introduction to a simplified configuration system for lp, author Peter Gray of the [[University of Wollongong]] described several weaknesses of the version shipping with the then-current [[Solaris (operating system)]] version 2.

*As opposed to the single daemon used by the simpler BSD lpr system, the lp system used separate daemons, one for scheduling and one for remote communication.
*The lpr system could be controlled with a single configuration file while lp requires a separate program for administration.
*The lp system did support permissions, but the model did not scale to hundreds of users.

As a result, Gray observed that "many administrators choose to simply run the old lpr/lpd system on the SVR4 boxes."<ref name=Gray1997/>

==See also==
* [[Berkeley printing system]]
* [[Common Unix Printing System]] (CUPS)
* [[LPRng]]

==References==
{{Reflist | refs=
<ref name=Kofler1997>{{cite book| title=Linux: Installation, configuration and use | last=Kofler | first=Michael | publisher=Addison-Wesley | year=1997 | isbn=0-201-17809-5 | chapter=6.4 Printer Configuration | pages=146&ndash;150}}</ref>
<ref name=Arthur1986>{{cite book | title=Unix Shell Programming | last=Arthur | first=Lowell Jay | publisher=John Wiley & Sons | year=1986 | isbn=0-471-84932-4 | pages=190}}</ref>
<ref name=Nemeth1985>{{cite book | title=UNIX System Administration Handbook | last1=Nemeth | first1=Evi | last2=Snyder | first2=Garth | last3=Seebass | first3=Scott | publisher=Prentice Hall | isbn=0-13-933441-6 | year=1989 | chapter=Printing Under ATT | pages=[https://archive.org/details/isbn_0139334416/page/164 164&ndash;173] | edition=1st | url=https://archive.org/details/isbn_0139334416/page/164 }} </ref>
<ref name=Rosen1990>{{cite book | title=UNIX System V Release 4: An Introduction for New and Experienced Users | url=https://archive.org/details/unixsystemvrelea00rose/page/117 | url-access=registration | last1=Rosen | first1=Kenneth H. | last2=Rosinski | first2=Richard R. | last3=Farber | first3=James M. | publisher=Osborne McGraw-Hill | year=1990 | isbn=0-07-881552-5 | pages=[https://archive.org/details/unixsystemvrelea00rose/page/117 117&ndash;121] }}</ref>
<ref name=Sobell1985>{{cite book | title=A Practical Guide to UNIX System V | last=Sobell | first=Mark G. | publisher=Benjamin/Cummings | year=1985 | isbn=0-8053-8915-6 | pages=45&ndash;46}}</ref>
<ref name=Gardner1994>{{cite book | title=Learning Unix | last=Gardner | first=James | publisher=SAMS | edition=2nd | year=1994 | isbn=0-672-30457-0 | pages=[https://archive.org/details/learningunix00gard/page/144 144] | url=https://archive.org/details/learningunix00gard/page/144 }}</ref>
<ref name=Cutler1994>{{cite book | title=SCO UNIX in a Nutshell | last=Cutler | first=Ellie | publisher=O'Reilly | year=1994 | isbn=1-56592-037-6 | pages=[https://archive.org/details/scounixinnutshel00elli/page/75 75&ndash;76] | url=https://archive.org/details/scounixinnutshel00elli/page/75 }}</ref>
<ref name=Welsh1995>{{cite book | title=Running Linux | last1=Welsh | first1=Matt | last2=Kaufman | first2=Lar | year=1995 | publisher=O'Reilly | edition=1st | isbn=1-56592-100-3 | page=[https://archive.org/details/runninglinux00wels_0/page/33 33] | url=https://archive.org/details/runninglinux00wels_0/page/33 }}</ref>  The same text is used in the 2nd (1996) edition.
<ref name=Welsh1999>{{cite book | title=Running Linux | year=1999 | edition=3rd | last1=Welsh | first1=Matt | last2=Dalheimer | first2=Kalle | last3=Kaufman | first3=Lar | isbn=1-56592-469-X | publisher=O'Reilly | pages=[https://archive.org/details/isbn_9781565924697/page/323 323&ndash;330] | url=https://archive.org/details/isbn_9781565924697/page/323 }}</ref>  The same text is used in the 4th (2003) edition.
<ref name=Smith2003>{{cite book | title=Linux Power Tools | last=Smith | first=Roderick W. | publisher=SYBEX | isbn=0-7821-4226-5 | year=2003 | chapter=Managing Printers | pages=269&ndash;284}}</ref>
<ref name=Gray1997>{{cite journal | title=Simplified LP configuration | pages=9&ndash;11 | journal=AUUGN: The Journal of AUUG (Australian Unix Systems User Group) | volume=18 | number=3 | date=August 1997 | url=https://books.google.com/books?id=AxULMRuVtWYC&pg=PA9 | last=Gray | first=Peter}}</ref>
}}

== External links ==
{{Wikibooks|Guide to Unix|Commands}}
* [https://web.archive.org/web/20030903234856/http://www.rahul.net/cgi-bin/userbin/man?topic=lp&section=1 lp]
* [http://www.rahul.net/cgi-bin/userbin/man?topic=lpstat&section=1 lpstat]
* [http://docs.sun.com/app/docs/doc/817-0403 Printing administration on Solaris 10]

{{Unix commands}}

[[Category:Computer printing]]
[[Category:UNIX System V]]