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.