LPD(8)

💖 LPD(8) — line printer spooler daemon 💖

okay bestie, gather round, because this is the manual page for lpd from the System Manager's Manual and it is literally the backbone of your whole printing situation. no cap. ✨

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🌸 NAME 🌸

lpd — line printer spooler daemon (yes that's the whole name, she's simple and she's iconic) 🎀

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✨ SYNOPSIS ✨

lpd [-dlrs] [-b bind-address] [-n maxchild] [-w maxwait] [port]

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💅 DESCRIPTION 💅

So. lpd is the line printer daemon (aka the spool area handler), and normally she gets woken up at boot time from the rc(8) file. Like, she's the main character who shows up first and gets everything ready. 🌈

She makes a single pass through the printcap(5) file to find out about the existing printers, and prints any files left after a crash. (yes she cleans up after the chaos, she's that girl) Then she uses the system calls listen(2) and accept(2) to receive requests to print files in the queue, transfer files to the spooling area, display the queue, or remove jobs from the queue. In each case, she forks a child to handle the request so the parent can continue to listen for more requests. multitasking queen fr fr 👑

The options are as follows:

• -b bind-address — Normally, if the -s option is not specified, lpd will listen on all network interfaces for incoming TCP connections. The -b option, followed by a bind-address, specifies that lpd should listen on that address instead of INADDR_ANY. Multiple -b options are permitted, allowing a list of addresses to be specified. Use of this option silently overrides the -s option if it is also present on the command line. (sneaky!!) bind-address can be a numeric host name in IPV4 or IPV6 notation, or a symbolic host name which will be looked up in the normal way. 🌐
• -d — The -d option turns on the SO_DEBUG socket(2) option. See setsockopt(2) for more details. 🐛
• -l — The -l flag causes lpd to log valid requests received from the network. This can be useful for debugging purposes. receipts, bestie, we love receipts 📝
• -n maxchild — The -n flag sets maxchild as the maximum number of child processes that lpd will spawn. The default is 32. 👶
• -r — The -r flag allows the “of” filter to be used if specified for a remote printer. Traditionally, lpd would not use the output filter for remote printers. so this is the glow-up option ✨
• -s — The -s flag selects “secure” mode, in which lpd does not listen on a TCP socket but only takes commands from a Unix domain socket. This is valuable when the machine on which lpd runs is subject to attack over the network and it is desired that the machine be protected from attempts to remotely fill spools and similar attacks. protect her!! she's in her secure era!! 🛡️
• -w maxwait — The -w flag sets maxwait as the wait time (in seconds) for dead remote server detection. If no response is returned from a connected server within this period, the connection is closed and a message logged. The default is 300 seconds. ⏰

If the [port] parameter is passed, lpd listens on this port instead of the usual “printer/tcp” port from /etc/services. 🚪

Now, the access control tea: Access control is provided by two means. First, all requests must come from one of the machines listed in the file /etc/hosts.equiv or /etc/hosts.lpd (which follows the same syntax as hosts.equiv(5)). Second, if the “rs” capability is specified in the printcap(5) entry for the printer being accessed, lpr requests will only be honored for those users with accounts on the machine with the printer. 🔐

lpd performs reverse DNS lookups on network clients. If a client hostname cannot be determined from its IP address, the print request will be silently dropped. 💀 silently!! no error, just gone!! This is important to note when debugging print problems in dynamic address environments. iykyk

The file minfree in each spool directory contains the number of disk blocks to leave free so that the line printer queue won't completely fill the disk. The minfree file can be edited with your favorite text editor. 🍓

The daemon begins processing files after it has successfully set the lock for exclusive access (described a bit later), and scans the spool directory for files beginning with cf. Lines in each cf file specify files to be printed or non-printing actions to be performed. Each such line begins with a key character to specify what to do with the remainder of the line. okay here comes the alphabet of it all, stay with me 💖

• J — Job Name. String to be used for the job name on the burst page. 📛
• C — Classification. String to be used for the classification line on the burst page. 🏷️
• L — Literal. The line contains identification info from the password file and causes the banner page to be printed. 📄
• T — Title. String to be used as the title for pr(1). 📝
• H — Host Name. Name of the machine where lpr(1) was invoked. 🖥️
• P — Person. Login name of the person who invoked lpr(1). This is used to verify ownership by lprm(1). 🫵
• M — Send mail to the specified user when the current print job completes. 📧
• f — Formatted File. Name of a file to print which is already formatted. 📁
• l — Like “f” but passes control characters and does not make page breaks. 🎛️
• p — Name of a file to print using pr(1) as a filter. 🌊
• t — Troff File. The file contains troff(1) output (cat phototypesetter commands). 🐈
• n — Ditroff File. The file contains device independent troff output. 🔄
• r — DVI File. The file contains Tex l output DVI format from Stanford. 🎓
• g — Graph File. The file contains data produced by plot. 📈
• c — Cifplot File. The file contains data produced by cifplot. 📊
• v — The file contains a raster image. 🖼️
• r — The file contains text data with FORTRAN carriage control characters. (yes bestie, r shows up twice in this list, that's not a typo on my part, that's just how the original is 💀)
• 1 — Troff Font R. Name of the font file to use instead of the default. 🔤
• 2 — Troff Font I. Name of the font file to use instead of the default. 🔤
• 3 — Troff Font B. Name of the font file to use instead of the default. 🔤
• 4 — Troff Font S. Name of the font file to use instead of the default. 🔤
• W — Width. Changes the page width (in characters) used by pr(1) and the text filters. 📏
• I — Indent. The number of characters to indent the output by (in ASCII). ➡️
• U — Unlink. Name of file to remove upon completion of printing. 🗑️
• N — File name. The name of the file which is being printed, or a blank for the standard input (when lpr(1) is invoked in a pipeline). 🧵

If a file cannot be opened, a message will be logged via syslog(3) using the LOG_LPR facility. lpd will try up to 20 times to reopen a file it expects to be there, after which it will skip the file to be printed. she tries so hard 🥺 but she also knows when to move on

lpd uses flock(2) to provide exclusive access to the lock file and to prevent multiple daemons from becoming active simultaneously. If the daemon should be killed or die unexpectedly, the lock file need not be removed. chill, it's fine The lock file is kept in a readable ASCII form and contains two lines. The first is the process ID of the daemon and the second is the control file name of the current job being printed. The second line is updated to reflect the current status of lpd for the programs lpq(1) and lprm(1). 🔒

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🎀 FILES 🎀

• /etc/printcap — printer description file 📋
• /var/run/lpd.pid — lock file for lpd 🔐
• /var/spool/output/* — spool directories 📂
• /var/spool/output/*/minfree — minimum free space to leave 🗂️
• /dev/lp* — line printer devices 🖨️
• /var/run/printer — socket for local requests 🔌
• /etc/hosts.equiv — lists machine names allowed printer access 📜
• /etc/hosts.lpd — lists machine names allowed printer access, but not under same administrative control. 🧾

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🌈 SEE ALSO 🌈

lpq(1), lpr(1), lprm(1), syslog(3), hosts(5), hosts.equiv(5), printcap(5), resolv.conf(5), lpc(8), pac(8)

4.3BSD Line Printer Spooler Manual. 📚

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👑 HISTORY 👑

An lpd daemon appeared in Version 6 AT&T UNIX. she's ancient and she's thriving, a true legend 🦋

lpd previously required that clients connected using a privileged port (below 1024). This restriction was removed because it does not provide additional security and also because many modern clients connect using an unprivileged port. growth!! evolution!! we love to see it ✨

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and that's the whole page bestie!! 💖 this one shipped with Debian, dated April 15, 2008 — like, old money but still serving. go print something, you've got this 🫶