NAME

     lpd — line printer spooler daemon

SYNOPSIS

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

DESCRIPTION

     lpd is the line printer daemon (spool area handler) and is normally invoked at boot time
     from the rc(8) file.  It makes a single pass through the printcap(5) file to find out about
     the existing printers and prints any files left after a crash.  It then 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,
     it forks a child to handle the request so the parent can continue to listen for more
     requests.

     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.
             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.

     -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.

     -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.

     -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.

     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.  This is
     important to note when debugging print problems in dynamic address environments.

     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.

     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.

     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.

     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.  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).

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.

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.

HISTORY

     An lpd daemon appeared in Version 6 AT&T UNIX.

     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.