On Tue, Oct 20, 2020 at 10:10:30PM -0400, Predrag Punosevac wrote: > > Every now and then people post a "question" about printing to this > mailng list which exposes their confusion. I am putting this email > together so that anybody capable of searching through the mailing list > can at least have terminology straight before asking for help. > Information presented here is in the public domain and I make no claims > of posting anything new. > > > Table of Contents: > > 1. Print spooling overview: LPD, LPRng, CUPS > 2. Common network printing protocols: LPD, IPP, JetDirect > 3. Printer driver. > 4. Input filters > 5. ASCII and page description language PostScript(PS) > 6. PostScript Printer Description (PPD) files > 7. Printer recommendations > 8. Code contribution > > > 1. What is a print spooling? Why is needed? > > A print spooler is a program/daemon that accepts print jobs from a > program or network. It typically consist of two programs: a print > spooler daemon that sends jobs to a printer and a command to submit > print jobs to the spooler daemon. In general spooler is not needed on > an operating system that allows a single user to perform only one task > at a time as long as that single user doesn't try to send multiple > documents to the printer at the same time. > > However, UNIX has been designed multitasking, multiuser computer > operating systems. Imagine that my wife and I send two documents to a > printer at the same time. Her documents gets there first and gets > printed. My document losses the race and my job is rejected because the > device is busy. I wait a few minutes and I sent my document again but > this time my daughter outrace me and her document get printed and not > mine. Now imagine the organization with hundreds of users and only a few > printers. This is exactly why we need a spooler program/daemon which > will listen for the incoming printing requests, stores them in a spool > queue, and then sends them to a printer when it becomes available. > > The original Berkeley spooling system is The Line Printer Daemon > protocol/Line Printer Remote protocol (or LPD) and it is available on > any default OpenBSD installation. LPD is super simple and writing a lpd > daemon should not be a too difficult for an undergraduate CS student. > For those of us who are old enough to remember legendary Richard Stevens > > https://www.oreilly.com/library/view/advanced-programming-in/9780321638014/ch21.html > > As the computer technology and printing proliferated among common folks > like me some system admins felt the need to develop more complex > queueing policies. People start hitting limitations of LPD and > eventually Dr. Patrick Powell felt compel to rewrite a new spooler > program/daemon which will be more capable of complex printing policies > and easier to incorporate drivers and input filters (please see below) > so the UNIX world got > > LPRng > > http://web.mit.edu/ops/services/print/Attic/src/doc/LPRng-HOWTO.html#toc2 > > as the project grew and never became truly financially viable eventually > was replaced with newer and super complex spooling system called CUPS > > https://www.cups.org/documentation.html > > Now the true CUPS claim to fame is the support for the new Internet > printing protocol (IPP). > > > 2. What are network printing protocols? > > From its inception UNIX was designed to a distributed computing > environment. A bunch of developers will use dumb terminals to connect to > the same computer and do some work. At the same time it became possible > for printers to be first class citizens on the LAN. LPD is not just a > spooling system it is also a network protocol spoken by the daemon > itself but also spoken by any decent quality printer. The major > limitation of LPD that is primarily single direction protocol. > > As printer became more sophisticated and more like a computers than > microcontroller boards it became obvious that one could ask the printer > about the level of the toner or the state of key mechanical components > (drum comes to mind). Thus we got IPP. Actually, we got more than that. > Most so called workgroup printers come with a built in CUPS server. > > That is not it. Manufacturer came up with many different network > protocols. I will mention the one I use JetDirect. From wikipedia page: > AppSocket, also known as Port 9100, RAW, JetDirect, or Windows TCPmon is > a protocol that was developed by Tektronix. It is considered as 'the > simplest, fastest, and generally the most reliable network protocol used > for printers > > > 3. What are the printer drivers? Do I need them. > > In "old good times" all printers were capable of printing raw ASCII > code. You don't need any drivers to print raw ASCII text on most > business grade printers. As printers became more sophisticated users > wanted to print more complicated things like pictures as oppose to ASCII > art. One of earliest examples of page description language was stack > language developed by Adobe called PostScript (to be discussed more > later in this document). A high quality (expensive in old times) > printers came with built in interpreters for PostScript language. You > don't need a driver to print on such printers. > > Then various manufacturers came with the reduced set of instructions > like Printer Command Langauge (PCL). You do need a driver to print to > such printer. The good news is that many such drivers are freely > available in > > https://www.ghostscript.com/ > > but the story doesn't end there. Printer manufacturers came up with a > novel business concept for mass market. They decided to give crappy > printers essentially for free, offload all the work to OS/consumers' > computers and make a kill by selling ink. You DO need proprietary > drivers to print on such devices and they are not useful if you are > trying to print from your OpenBSD desktop unless you are planning to > smack your co-worker with such a device during a friendly office brawl. > High quality open source drivers beside vulnerable GhostScript are part > of packages like > > http://gimp-print.sourceforge.net/ > > or > > https://developers.hp.com/hp-linux-imaging-and-printing > > or even for crappy Samsung printers which need firmware > > http://splix.ap2c.org/ > > All these drivers are already ported to OpenBSD and maintained single > handedly for over 10-15 years by Anthony Jacotot.
Wow, I could never have imagined so many typos in my name :-) > 4. What are the Input filters? Do I need them? > > No you don't need them. As long as you buy a decent quality printer > which some with the built in PostScript interpreter and you never send > anything to that printer except the PostScript file you are golden. For > the rest of us which are less perfect various input filters come to the > rescue. The most primitive input filter is just a shell script or Perl > script which parses your file and decides on the type of the file. Than > it calls an auxiliary program which converts the file to the PostScript > language. Finally if the printer doesn't speak complete PostScript but > some kind reduced version like PCL it calls the driver to convert the > PostScript stream into the language spoken by printer (PCL is very > common) before sending it to the printer. This is the simplest possible > example of such a filter is shamelessly stollen from NetBSD > documentation > > #!/bin/sh > # Treat LF as CR+LF > printf "\033&k2G" || exit 2 > # Print the postscript file > /usr/pkg/bin/gs -dSAFER -dBATCH -dQUIET -dNOPAUSE -q -sDEVICE=cdj550 \ > -sOutputFile=- -sPAPERSIZE=a4 - && exit 0 > exit 2 > > > > If you don't know what is your printer capable of maybe you should learn > a bit of SNMP protocol. > > snmpwalk -c public 10.0.1.19 .1.3.6.1.4.1.2699.1.2 > > where 10.0.1.19 is the IPv4 of your network printer. > This is one of my favorite printing posts and Greg Woods really knows > what he is talking about > > https://marc.info/?l=netbsd-users&m=159389498001287&w=2 > > I wormly recommend searching mailing lists archives for his posts. > > I would like to finish this section mentioning a few well known input > filters which are not exactly one liners. > > http://ports.su/print/apsfilter > > or much newer which I use > > https://wiki.linuxfoundation.org/openprinting/database/foomatic > > Be careful with the last one foomatic people disabled the support for > LPD a few years ago. That is why whe have to have a work around. Make > sure you read pkg-readme which comes with cups-filters (yes they even > renamed they stupid filter after the CUPS). > > > 5. ASCII and page description language PostScript(PS) > > By this section we already mentioned that all decent quality printers > should be able to print ASCII code without any drivers. As of page > description language PostScript(PS) I would just say that is a true > stack based programming language (I think it is inspired by my favorite > programming language Forth). > > > https://www.adobe.com/jp/print/postscript/pdfs/PLRM.pdf > > In "old good times" while growing up behind the Iron curtain I as many > other people learnt to hack PostScript files by hand to make them > printable to the crappy printers (we could not effort to buy good once > from the West). > > It is also an excellent tool for teaching geometry > > http://www.math.ubc.ca/~cass/courses/m308-7b/ch1.pdf > > but these days I only teach my own daughters. A "common trick" in old > times would be a getting a PostScript module from a junk yard > > https://www.ebay.com/p/1625921313 > > and putting it in the cheap printer, instantaneous converting it to > the decent quality printer. > > > > 6. What the hack are PostScript Printer Description (PPD) files? > > Those are not drivers? They are simple see below text files describing > capabilities of your printer to the Input filter. > > *%================================================ > *% Copyright(C) 2005 Brother Industries, Ltd. > *% "Brother HL-5250DN BR-Script3" > *%================================================ > > *%==== General Information Keywords ======================== > *FormatVersion: "4.3" > *FileVersion: "1.03" > *LanguageEncoding: ISOLatin1 > *LanguageVersion: English > *Manufacturer: "Brother" > *PCFileName: "BR5250_2.PPD" > *Product: "(Brother HL-5250DN series)" > *PSVersion: "(3010.106) 5" > *ShortNickName: "Brother HL-5250DN BR-Script3" > *ModelName: "Brother HL-5250DN BR-Script3" > *NickName: "Brother HL-5250DN BR-Script3" > *1284DeviceID: "MFG:Brother;MDL:HL-5250DN > series;CMD:PJL,PCL,PCLXL,POSTSCRIPT;" > > *%==== Basic Device Capabilities ============= > *LanguageLevel: "3" > *TTRasterizer: Type42 > *ColorDevice: False > *DefaultColorSpace: Gray > *FileSystem: True > *?FileSystem:" > save > /devname (%disk0%) def > /ret false def > 0 1 7{ > devname exch 48 add 5 exch put > devname devstatus { > 0 ne {/ret true def}if > pop pop pop pop pop pop pop > }if > }for > ret {(True)}{(False)} ifelse = flush > restore > " > *End > > *Throughput: "28" > *FreeVM: "6050000" > > *%==== Emulations and Protocols ========== > *Protocols: PJL TBCP > > *SuggestedJobTimeout: "0" > *SuggestedWaitTimeout: "300" > *PrintPSErrors: True > > > 7. Could you give me some recommendation for a printer? > > Sure. I like Brother monochromatic laser printers like this one. > > https://www.amazon.com/Brother-HL-5250DN-Network-Printer-Duplex/dp/B000BQ535K > > They speak PostScript or at least PCL6. They come with a built in CUPS > server (you will need to use CUPS on your OpenBSD desktop if you want to > print that way) but they also support DirectJet Protocol > > oko# cat /etc/printcap > # Remote printer must use jetdirect since foomatic-rip doesn't speak LPD > rp|HL-5250DN:\ > :[email protected]:\ > :if=/etc/foomatic-rip/script_brother.sh:\ > :sh:sd=/var/spool/output/brother:\ > :lf=/var/log/lpd-errs: > > oko# cat /etc/foomatic-rip/script_brother.sh > #!/bin/sh > > /usr/local/bin/a2ps -BRq --columns=1 -o - | \ > /usr/local/bin/foomatic-rip -P HL-5250DN --ppd \ > /etc/foomatic-rip/direct/brother-hl-5250dn-postscript-brother.ppd > > > If you want to print Duplex don't forget to embed > > > %! > <</Duplex true>>setpagedevice > > at the beginning of a PostScript file you are trying to print > > Or for example using a2ps filter from Xpdf. > > predrag@oko$ head .xpdfrc > # Set the default PostScript file or command. > psFile "|a2ps -Prp -1 -s2" > psPaperSize letter > > # launch URLs in Firefox > urlCommand "firefox-esr '%s'" > > # launch movie annotations in mplayer > movieCommand "/usr/local/bin/mplayer %s" > > > In "old good times" HP priters were the Gold standard. HP LaserJet 4 > lasted me for 15 years and was still usable but getting a bit slow for > my work flow. > > > > 8. Code contribution? > > You read this post and you feel like you could contribute to UNIX > printing. Why not hack on the LPD itself. At some point Eric Faurot was > working on the new lpd server for OpenBSD > > https://undeadly.org/cgi?action=article;sid=20180509184829 > > > Why don't go step further and implement IPP protocol inside LPD? Who > need CUPS? > > > > Most Kind Regards, > Predrag Punosevac > -- Antoine
