LPD(8) | System Manager's Manual | LPD(8) |
lpd
—
lpd |
[-dlsrW ] [-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.
Available options:
-b
-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
-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” and
“if” filters to be used if specified for a remote printer.
Traditionally, lpd
would not use filters 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
-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
-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.
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).
4.3 BSD Line Printer Spooler Manual.
lpd
daemon appeared in Version 6 AT&T UNIX.
January 20, 2006 | NetBSD 9.4 |