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 thatlpd
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 theSO_DEBUG
socket(2) option. See setsockopt(2) for more details. -l
- The
-l
flag causeslpd
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 thatlpd
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 whichlpd
does not listen on a TCP socket but only takes commands from a UNIX domain socket. This is valuable when the machine on whichlpd
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.