NAME
lpd —
line printer spooler
daemon
SYNOPSIS
lpd |
[-dlsrW]
[-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.
Available options:
-
-
- -b
- 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
- 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”
and “if” filters to be used if specified for a remote printer.
Traditionally, lpd would not use filters 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
- 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 120 seconds.
-
-
- -W
- The -W option will instruct lpd not to
verify a remote tcp connection comes from a reserved port (<1024).
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 three means. First,
/etc/hosts.allow and
/etc/hosts.deny are
consulted as described in
hosts_access(5) with
daemon name
lpd. Second, all requests must come from one of
the machines listed in the file
/etc/hosts.equiv or
/etc/hosts.lpd unless there is a line consisting of
‘+’, in which case any host will be accepted that passes the
hosts_access(5) test and
has reverse resolving set up. Lastly, 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. Requests must
pass all three tests.
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.
-
-
- d
- 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.
-
-
- o
- The file contains PostScript data.
-
-
- 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/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.allow
- explicit remote host access list.
- /etc/hosts.deny
- explicit remote host denial of service list.
- /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),
setsockopt(2),
syslog(3),
hosts.equiv(5),
hosts_access(5),
hosts_options(5),
printcap(5),
lpc(8),
pac(8)
4.3 BSD Line Printer Spooler
Manual.
HISTORY
An
lpd daemon appeared in Version 6 AT&T UNIX.