printer spooler daemon
is the line printer daemon (spool area handler)
and is normally invoked at boot time from the
file. It makes a
single pass through the
to find out about the existing printers and prints any files left after a
crash. It then uses the system calls
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
The options are as follows:
- 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.
- The -d option turns on the
for more details.
- The -l flag causes
lpd to log valid requests received from the
network. This can be useful for debugging purposes.
- The -n flag sets
maxchild as the maximum number of child
processes that lpd will spawn. The default is
- 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.
- 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.
- 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,
listens on this port instead of the usual
“printer/tcp” port from
Access control is provided by two means. First, all requests must come from one
of the machines listed in the file
, one hostname per line. A plus
"+" may be used as a wildcard to grant access to all hosts. Second,
if the “rs” capability is specified in the
for the printer being accessed, lpr
only be honored for those users with accounts on the machine with the printer.
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
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.
- Job Name. String to be used for the job name on the burst
- Classification. String to be used for the classification
line on the burst page.
- Literal. The line contains identification info from the
password file and causes the banner page to be printed.
- Title. String to be used as the title for
- Host Name. Name of the machine where
- Person. Login name of the person who invoked
lpr(1). This is
used to verify ownership by
- Send mail to the specified user when the current print job
- Formatted File. Name of a file to print which is already
- Like “f” but passes control characters and
does not make page breaks.
- Name of a file to print using
pr(1) as a
- Troff File. The file contains troff output (cat
- Ditroff File. The file contains device independent troff
- DVI File. The file contains Tex l output DVI format from
- Graph File. The file contains data produced by
- Cifplot File. The file contains data produced by
- The file contains a raster image.
- The file contains text data with FORTRAN carriage control
- Troff Font R. Name of the font file to use instead of the
- Troff Font I. Name of the font file to use instead of the
- Troff Font B. Name of the font file to use instead of the
- Troff Font S. Name of the font file to use instead of the
- Width. Changes the page width (in characters) used by
pr(1) and the text
- Indent. The number of characters to indent the output by
- Unlink. Name of file to remove upon completion of
- 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
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.
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
for the programs
- printer description file
- spool directories
- minimum free space to leave
- line printer devices
- socket for local requests
- lists machine names allowed printer access
4.3BSD Line Printer Spooler
daemon appeared in
Version 6 AT&T UNIX
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.