LPD(8) BSD System Manager's Manual LPD(8)NAMElpd - line printer spooler daemon
SYNOPSISlpd [-dlsrW] [-b bind-address] [-n maxchild] [-w maxwait] [port]
DESCRIPTIONlpd is the line printer daemon (spool area handler) and is normally in-
voked 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 Normally, if the -s option is not specified, lpd will listen on
all network interfaces for incoming TCP connections. The -b op-
tion, 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" 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 sock-
et. This is valuable when the machine on which lpd runs is sub-
ject 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 con-
nected server within this period, the connection is closed and a
message logged. The default is 300 seconds.
-W The -W option will instruct lpd not to verify a remote tcp con-
nection 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 two means. First, all requests must come
from one of the machines listed in the file /etc/hosts.equiv or
/etc/hosts.lpd. 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 direc-
tory 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 com-
pletes.
f Formatted File. Name of a file to print which is already format-
ted.
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 photo-
typesetter commands).
n Ditroff File. The file contains device independent troff output.
r DVI File. The file contains Tex l output DVI format from Stan-
ford.
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 charac-
ters.
1 Troff Font R. Name of the font file to use instead of the de-
fault.
2 Troff Font I. Name of the font file to use instead of the de-
fault.
3 Troff Font B. Name of the font file to use instead of the de-
fault.
4 Troff Font S. Name of the font file to use instead of the de-
fault.
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 pipe-
line).
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 ex-
pects 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 dae-
mon should be killed or die unexpectedly, the lock file need not be re-
moved. 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 ALSOlpq(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.
MirOS BSD #10-current May 18, 2002 2
