LPD(8) | System Manager's Manual | LPD(8) |
lpd
— line printer
spooler daemon
lpd |
[-dlrs ] [-b
bind-address] [-n
maxchild] [-w
maxwait] [port] |
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-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
-d
option turns on the
SO_DEBUG
socket(2) option. See
setsockopt(2) for more details.-l
-l
flag causes lpd
to
log valid requests received from the network. This can be useful for
debugging purposes.-n
maxchild-n
flag sets maxchild as
the maximum number of child processes that lpd
will spawn. The default is 32.-r
-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
-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-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.
plot
.cifplot
.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).
lpd
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.
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.
April 15, 2008 | Debian |