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15	<H2><A NAME="rfc1179ref"></A> <A NAME="s18">18. RFC 1179 - Line Printer Daemon Protocol</A></H2>
16
17	<P>RFC1179 can be obtained from the LPRng distribution, in the LPRng_DOC/rfc1179 directory,
18	or from one of many sites which mirror the RFCs.
19	<P>This RFC is an <EM>informational</EM> RFC,
20	which means that the information in it is meant as a guide to users,
21	and not as a fixed standard.
22	In addition,
23	the RFC tried to document the behavior of the BSD LPD print server,
24	and left out many details dealing with error recover,
25	error messages,
26	extensions to the protocol,
27	etc.
28	<P>In this section,
29	I will try to explain what RFC1179 specifies as a protocol,
30	and many of the problems encountered in trying to use it.
31	<H2><A NAME="socketlinger"></A> <A NAME="retrynolink"></A> <A NAME="retryeconnrefused"></A> <A NAME="reuseaddr"></A> <A NAME="originateport"></A> <A NAME="lpdport"></A> <A NAME="ss18.1">18.1 Ports and Connections</A>
32	</H2>
33
34	<P>Options used:
35	<UL>
36	<LI> <CODE>lpd_port=</CODE><EM>Port for LPD to accept connection</EM></LI>
37	<LI> <CODE>originate_port=</CODE><EM>Ports to originate connections on</EM></LI>
38	<LI> <CODE>reuse_addr</CODE><EM>  Set SO_REUSEADDR flag on connection</EM></LI>
39	<LI> <CODE>retry_econnrefused</CODE><EM>  Retry on connect ECONNREFUSED error</EM></LI>
40	<LI> <CODE>retry_nolink</CODE><EM>  Retry on device open or connection ffailure</EM></LI>
41	<LI> <CODE>socket_linger#</CODE><EM>  Linger time for sockets</EM></LI>
42	</UL>
43	<P>RFC1179 requires that the <CODE>lpd</CODE> server listen for TCP/IP connections
44	on port 515.
45	This port is registered with the Internet Naming Authority,
46	and the <CODE>/etc/services</CODE> file or TCP/IP services database usually has an entry:
47	<BLOCKQUOTE><CODE>
48	<PRE>
49	printer 515/tcp spooler # line printer spooler
50	</PRE>
51	</CODE></BLOCKQUOTE>
52	<P>RFC1179 explicitly states that all connections to port 515 must originate from
53	ports 721-731.
54	The reason for this restriction is due to the UNIX concept of <EM>reserved</EM>
55	and <EM>privileged</EM> ports.
56	By convention,
57	ports in the range 1-1023 can only <B>bound</B> by processes whose Effective User ID (EUID)
58	is 0 (root).
59	This,
60	ordinary users could not originate a connection from the reserved or privileged port range.
61	<P>In a UNIX environment, this means that the user programs
62	<CODE>lpr</CODE>,
63	<CODE>lprm</CODE>,
64	<CODE>lpq</CODE>,
65	and
66	<CODE>lpc</CODE>
67	would have to be SETUID root.
68	<P>As experience has shown, for security purposes,
69	the fewer programs that need to have privileged status,
70	the better.
71	LPRng uses the
72	<CODE>lpd_port=printer</CODE> configuration option to set the actual port to be use.
73	By default, this is port 515, but can be set to other values.
74	<P>The restriction of originating ports to 721-731 causes another set of problems.
75	Part of the TCP/IP protocol is concerned with avoiding communications problems
76	resulting from the arrival of old or <EM>stale</EM> packets.
77	When a connection between
78	<CODE>sourcehost, sourceport</CODE> and <CODE>desthost, destport</CODE>
79	is made,
80	a set of sequence numbers is established and used for sending and acknowledgement of data.
81	When the connection terminates,
82	the TCP/IP protocol restricts the establishment of a new connection between
83	<CODE>sourcehost, sourceport</CODE> and <CODE>desthost, destport</CODE> for a period long
84	enough for all <EM>stale</EM> packets to be removed from the system.
85	This is approximately 10 minutes long.
86	<P>In order to simplify assignments of ports,
87	timing out connections, and other matters,
88	many TCP/IP packages do keep track of explicit connections
89	<EM>originating</EM> from a port,
90	but simply prevent the port from being reused for either origination
91	or reception of a connection.
92	They do,
93	however,
94	keep track of the active connections <B>to</B> a port,
95	and perform timeouts on these.
96	This is usually much simpler to implement,
97	as it can be done with a list attached to the port.
98	<P>This implementation method creates some problems when
99	a large number of connections must be originated from a
100	relatively small number of port numbers.
101	Observe what happens when host 1 tries to send a large number of jobs to a server 2.
102	The following connections are established and terminated:<BR>
103	<CODE>host 1, port 721</CODE> and <CODE>host 2, port 515</CODE><BR>
104	<CODE>host 1, port 722</CODE> and <CODE>host 2, port 515</CODE><BR>
105	<CODE>host 1, port 723</CODE> and <CODE>host 2, port 515</CODE><BR>
106	<CODE>host 1, port 724</CODE> and <CODE>host 2, port 515</CODE><BR>
107	<CODE>host 1, port 725</CODE> and <CODE>host 2, port 515</CODE><BR>
108	<CODE>host 1, port 726</CODE> and <CODE>host 2, port 515</CODE><BR>
109	<CODE>host 1, port 727</CODE> and <CODE>host 2, port 515</CODE><BR>
110	<CODE>host 1, port 728</CODE> and <CODE>host 2, port 515</CODE><BR>
111	<CODE>host 1, port 729</CODE> and <CODE>host 2, port 515</CODE><BR>
112	<CODE>host 1, port 730</CODE> and <CODE>host 2, port 515</CODE><BR>
113	<CODE>host 1, port 731</CODE> and <CODE>host 2, port 515</CODE>
114	<P>Now according to the RFC1179 rules and the TCP/IP protocol,
115	we will have to wait until one of these connections terminates before we
116	can make another.
117	On the originating system,
118	if the TCP/IP implementation does timeouts on the originating port,
119	we will have to wait for the timeout to elapse before we can make a new
120	connection.
121	Unfortunately, there is no way to find out what the status of the port
122	is, so we will have to try them each in turn until we get
123	a successful connection.
124	<P>The LPRng code has tried to provide several methods to deal with
125	these problems.
126	Firstly,
127	the
128	<CODE>originate_port=512 1023</CODE>
129	option specifies the range
130	of ports used to originate connections
131	when the software is running either as ROOT or SETUID root.
132	By strict RFC1179 rules,
133	this should be
134	<CODE>originate_port=721 731</CODE>,
135	but it turns out that most BSD LPD based implementations only
136	check for a <EM>reserved</EM> originating port.
137	By using 512 ports we get a greatly reduced rate of errors due
138	to lack of ports due to pending timeouts.
139	<P>However,
140	on some systems which are acting as servers for a large number of
141	printers even increasing this port range is insufficient,
142	and steps need to be taken use the originating port numbers
143	more efficiently.
144	The Berkeley TCP/IP implementation
145	<CODE>getsockopt()</CODE>
146	and
147	<CODE>setsockopt()</CODE>
148	allows the user to manipulate some of the underlying timeouts and options
149	of the TCP/IP network.
150	When a TCP/IP connection is established,
151	the
152	<CODE>setsockopt()</CODE>
153	facility can be used to set the
154	<CODE>SO_REUSEADDR</CODE>
155	flag on the connection.
156	This flag effectively sets the timeout value on the ports
157	and connections to 0,
158	allowing immediate reuse of the ports.
159	When done on an originating end of a connection,
160	this will allow the originating port number to be reused immediately.
161	<P>It would appear that by setting
162	<CODE>SO_REUSEADDR</CODE>
163	on the originating end that we have solved our problems.
164	However,
165	unless the destination end of the connection sets its
166	<CODE>SO_REUSEADDR</CODE>
167	flag on the connection,
168	it will still do a timeout.
169	Thus when we try to make a connection from a port
170	that was active within a short period of time to the
171	same host,
172	then it will reject the connection until the
173	timeout is over.
174	<P>The
175	<CODE>reuse_addr</CODE>
176	flag (default off) forces
177	the LPRng software to set the
178	<CODE>SO_REUSEADDR</CODE>
179	flag on originating connections.
180	As indicated,
181	this will allow ports to be reused immediately for outgoing connections,
182	rather than waiting for a timeout.
183	<P>While the
184	<CODE>reuse_addr</CODE>
185	flag usually allows us to reuse ports,
186	there is still the problem of dealing with connections failing due to the
187	remote site rejecting the connection due to a pending timeout
188	from a previous connection.
189	A careful study of the original BSD TCP/IP network code and of some
190	others indicates that when a connection fails due to a pending timeout,
191	an ECONNREFUSED error code is returned to a
192	<CODE>connect()</CODE> system call.
193	If this happens and we suspect that the remote site is rejecting
194	the connection due to a timeout problem,
195	then we should retry making the connection but from a new port,
196	and continue retrying until all possible ports are used.
197	<P>The <CODE>retry_econnrefused</CODE> (default on) flag is used to
198	specify that we retry connections in this manner.
199	When this is set,
200	a <CODE>connection refused</CODE>
201	error causes the connection to be retried using a new port.
202	This will be repeated until all available ports have been tried.
203	<P>When
204	printing a job and the <CODE>lpd</CODE> server connection to a remote
205	site or device open fails,
206	the <CODE>retry_nolink</CODE> (default on)
207	will cause the attempt to be retried indefinitely.
208	The combination of <CODE>retry_econnrefused</CODE> and <CODE>retry_nolink</CODE>
209	will provide robust connection attempts to remote systems.
210	<P>While the above problems cause difficulties when making connections,
211	there are also problems when terminating connections.
212	After closing a socket,
213	the TCP/IP software will try to flush any pending data to the destination.
214	Unfortunately,
215	on some systems it will only do this while the process is active.
216	This has caused problems on systems which terminate
217	a process it has received an abnormal (signal caused) termination.
218	<P>The <CODE>setsockopt()</CODE> SO_LINGER option allows the user to specify
219	that when a socket is closed normally,
220	that the process should block until pending data is flushed or
221	for the <CODE>socket_linger</CODE> period.
222	If <CODE>socket_linger</CODE> is 0,
223	then no SO_LINGER operation is done.
224	<P>In summary, if you experience problems with connection failures due
225	to port exhaustion,
226	first try setting the
227	<CODE>reuse_port</CODE> flag,
228	and you should see a reduction.
229	Check to ensure that the <CODE>retry_econnrefused</CODE>
230	and <CODE>retry_nolink</CODE> flags are set,
231	and the error code in the log and status files.
232	If the failures continue, then the problem is caused by the
233	remote end having timeout limitations and there is little you
234	can do except to set a very long <CODE>connect_retry</CODE>
235	interval, say <CODE>connect_retry=120</CODE> (2 minutes).
236	<H2><A NAME="remotesupport"></A> <A NAME="ss18.2">18.2 Protocol Requests and Replies</A>
237	</H2>
238
239	<P>Options used:
240	<UL>
241	<LI> <CODE>remote_support=</CODE><EM>Remote operations supported</EM></LI>
242	</UL>
243	<P>After a connection has been established,
244	a request can be sent to the <CODE>lpd</CODE>
245	server.
246	The request consists of a single octet indicating the request type,
247	followed by the printer (or print queue) name, followed by
248	a set of options for the request,
249	followed by a LF (line feed) character.
250	<BLOCKQUOTE><CODE>
251	<PRE>
252	\NNNprinter[ options]\n
253	NNN Operation
254	</PRE>
255	</CODE></BLOCKQUOTE>
256	<P>
257	<CENTER><TABLE BORDER><TR><TD>
258	<BR>
259	NNN</TD><TD>RFC1179</TD><TD>Operation</TD><TD>program</TD></TR><TR><TD>
260	1</TD><TD>yes</TD><TD>start print</TD><TD><CODE>lpc</CODE></TD></TR><TR><TD>
261	2</TD><TD>yes</TD><TD>transfer a printer job</TD><TD><CODE>lpr</CODE></TD></TR><TR><TD>
262	3</TD><TD>yes</TD><TD>print short form of queue status</TD><TD><CODE>lpq</CODE></TD></TR><TR><TD>
263	4</TD><TD>yes</TD><TD>print long form of queue status</TD><TD><CODE>lpq</CODE></TD></TR><TR><TD>
264	5</TD><TD>yes</TD><TD>remove jobs</TD><TD><CODE>lprm</CODE></TD></TR><TR><TD>
265	6</TD><TD>LPRng</TD><TD>do control operation</TD><TD><CODE>lpc</CODE></TD></TR><TR><TD>
266	7</TD><TD>LPRng</TD><TD>transfer a block format print job</TD><TD><CODE>lpr</CODE></TD></TR><TR><TD>
267	8</TD><TD>LPRng</TD><TD>secure command transfer</TD><TD><CODE>lpc</CODE></TD></TR><TR><TD>
268	9</TD><TD>LPRng</TD><TD>verbose status information</TD><TD><CODE>lpq</CODE></TD></TR><TR><TD>
269
270	</TD></TR></TABLE></CENTER>
271	<P>After the request has been sent,
272	then a reply will be returned.
273	In general the reply has the following form:
274	<BLOCKQUOTE><CODE>
275	<PRE>
276	\000\n Success
277	\NNN\n Failure (NNN is error code)
278	text\n Text or status information
279	</PRE>
280	</CODE></BLOCKQUOTE>
281	<P>As can be seen,
282	this protocol is extremely simple,
283	but there are a set of problems due to the loosely written language of RFC1179.
284	<OL>
285	<LI>Firstly,
286	while RFC1179 sets limits on the lengths of commands,
287	it does not strictly set limits on the characters set used in the commands.
288	This can result in problems when trying to print status information,
289	headers on banners,
290	and other details.</LI>
291	<LI>The original RFC1179 protocol did not provide any way to do remote control
292	of queues or LPD servers.
293	This has been added to the protocol.
294	As a side effect,
295	if you try to use
296	<CODE>lpc</CODE> to control a non-LPRng printer,
297	it will not work.</LI>
298	<LI>You can specify that a network printer is non-LPRng by using the
299	<CODE>remote_support=RQVMC</CODE> option and specify the operations
300	supported by the printer.
301	The letters R, Q, V, M, and C stand for
302	<CODE>lpr</CODE>,
303	<CODE>lpq</CODE>,
304	<CODE>lpq -v</CODE> (verbose),
305	verbose <CODE>lpq</CODE>,
306	<CODE>lprm</CODE>,
307	and <CODE>lpc</CODE> operations respectively,
308	and indicate that these are supported.
309	If <CODE>remote_support</CODE> does not allow a particular operation,
310	then the LPRng software will not send a corresponding request to the printer.
311	For example,
312	<CODE>remote_support=R</CODE>
313	would restrict operations to spooling jobs only,
314	and the LPRng software would not query the printer for status.</LI>
315	</OL>
316	<H2><A NAME="useshorthost"></A> <A NAME="longnumber"></A> <A NAME="senddatafirst"></A> <A NAME="ss18.3">18.3 Job Transfer</A>
317	</H2>
318
319	<P>Options used:
320	<UL>
321	<LI> <CODE>longnumber</CODE><EM>  Long job number (6 digits)</EM></LI>
322	<LI> <CODE>send_data_first</CODE><EM>  Send data files first</EM></LI>
323	<LI> <CODE>use_shorthost</CODE><EM>  Use short hostname</EM></LI>
324	</UL>
325	<P>A job transfer operation starts with a job transfer request,
326	followed by several file transfer operations.
327	At the end of the file transfers,
328	the connection should be closed.
329	<P>A file transfer request has the form:
330	<CENTER><TABLE BORDER><TR><TD>
331	<BR>
332	Command</TD><TD>Purpose</TD></TR><TR><TD>
333	\001\n</TD><TD>abort</TD></TR><TR><TD>
334	\002nnnn cfname</TD><TD>control file transfer</TD></TR><TR><TD>
335	\003nnnn dfname</TD><TD>data file transfer</TD></TR><TR><TD>
336
337	</TD></TR></TABLE></CENTER>
338	<P>The abort operation is used to terminate job transfer and indicate that
339	the job should not be processed for printing.
340	The connection will be closed and the partly transferred job
341	will be discarded.
342	<P>The control file and data file transfer commands have a length (in bytes)
343	of the file and the name of the file to be transferred.
344	When the command is received,
345	the server will reply with a status line:
346	<CENTER><TABLE BORDER><TR><TD>
347	<BR>
348	Status</TD><TD>Purpose</TD></TR><TR><TD>
349	\000</TD><TD>Accepted, proceed</TD></TR><TR><TD>
350	\nnn</TD><TD>Rejected with error code</TD></TR><TR><TD>
351
352	</TD></TR></TABLE></CENTER>
353	<P>The reply is only a single octet.
354	Some defective implementations of RFC1179 send a LF after the octet,
355	which makes life very difficult.
356	LPRng makes an effort to detect these non-conforming RFC1179 systems
357	and will accept jobs from them.
358	However, it will not send jobs to them.
359	<P>If LPRng sends a reject code, as an extension to RFC1179 it also
360	sends an error message. Note that the values for error codes
361	are not defined,
362	nor are their causes.
363	LPRng uses the following values for error codes,
364	which appear to be compatible with many,
365	but not all, of the BSD LPD based systems:
366	<CENTER><TABLE BORDER><TR><TD>
367	<BR>
368	Code</TD><TD>Error</TD></TR><TR><TD>
369	\000</TD><TD>Accepted, proceed</TD></TR><TR><TD>
370	\001</TD><TD>Queue not accepting jobs</TD></TR><TR><TD>
371	\002</TD><TD>Queue temporarily full, retry later</TD></TR><TR><TD>
372	\003</TD><TD>Bad job format, do not retry</TD></TR><TR><TD>
373
374	</TD></TR></TABLE></CENTER>
375	<P>When the sender gets the reply indicating success,
376	it sends the <CODE>nnnn</CODE> bytes of the control or data file,
377	followed by a <CODE>\000</CODE> octet.
378	The receiver will then reply as above;
379	a single <CODE>\000</CODE> octet indicating success.
380	<P>The above procedure is carried out until all data files and the control
381	file of a job are transferred.
382	<P>RFC1179 is silent on the following issues:
383	<OL>
384	<LI>When sending a job,
385	do you send the control file first, followed by the data file(s),
386	or the data files first?</LI>
387	<LI>When sending multiple jobs,
388	can you send them on a single connection,
389	or do you have to establish a new connection for each job?</LI>
390	</OL>
391	<P>LPRng will <EM>accept</EM> jobs whether they are sent control or data files
392	first.
393	By default,
394	it sends the control file first,
395	followed by the data file.
396	If the destination system requires that the data files
397	be sent first,
398	the <CODE>send_data_first</CODE> printcap option can be used to force
399	data files to be sent first.
400	<P>RFC1179 states that:
401	<BLOCKQUOTE>
402	The name of the control file ... should start with ASCII "cfA", followed by a three
403	digit job number, followed by the host name which has constructed the
404	control file.
405	</BLOCKQUOTE>
406	<P>The <EM>should</EM> in this wording indicates that this is simply a guideline,
407	and that other formats are possible.
408	Some of the major problems with this format are as follows:
409	<OL>
410	<LI> The restriction to 3 digits means that at most 1000 jobs
411	can be in a queue.
412	Strangely, some systems generate far more than 1000 jobs a day,
413	and need to archive them on a regular basis.
414	The <CODE>longnumber</CODE> option will allow LPRng to use a 6 digit
415	job number for files in the print queue.</LI>
416	<LI>The host name format is not specified.
417	Some implementations consider that this is the short host name,
418	while others think it is the fully qualified domain name (FQDN).
419	LPRng,
420	by default,
421	will use the FQDN host name.
422	However, the <CODE>use_shorthost</CODE> option will force it to
423	use short host names in control and data files.</LI>
424	<LI>The <CODE>cfA</CODE> control file name was modified to allow the
425	job priority to be used as the A letter of the control file.
426	By default,
427	this is A (lowest, i.e. <CODE>cfA</CODE>) and
428	but can range to Z (highest, i.e. <CODE>cfZ</CODE>).
429	All known spoolers except LPRng seem to ignore the actual value of
430	the letter.</LI>
431	</OL>
432	<H2><A NAME="ss18.4">18.4 Data File Transfer</A>
433	</H2>
434
435	<P>As discussed,
436	a data file is transferred using the command below.
437	<CENTER><TABLE BORDER><TR><TD>
438	<BR>
439	Command</TD><TD>Purpose</TD></TR><TR><TD>
440	\003nnnn dfname</TD><TD>data file transfer</TD></TR><TR><TD>
441
442	</TD></TR></TABLE></CENTER>
443	<P>From RFC1179:
444	<BLOCKQUOTE>
445	The data file may contain any 8 bit values at all. The total number
446	of bytes in the stream may be sent as the first operand, otherwise
447	the field should be cleared to 0. The name of the data file should
448	start with ASCII "dfA". This should be followed by a three digit job
449	number. The job number should be followed by the host name which has
450	constructed the data file. Interpretation of the contents of the
451	data file is determined by the contents of the corresponding control
452	file.
453	</BLOCKQUOTE>
454	<P>There are several surprises in RFC1179.
455	<OL>
456	<LI>Apparently a job should only consist of a single data file.
457	This is a severe limitation, and in fact the BSD LPR and other
458	print spoolers process jobs with multiple data files.
459	By convention, these data files have names of the form
460	<CODE>dfA</CODE>,
461	<CODE>dfB</CODE>,
462	...
463	<CODE>dfZ</CODE>,
464	<CODE>dfa</CODE>,
465	<CODE>dfz</CODE>.</LI>
466	<LI>The RFC does not specify that the control file and data file job numbers
467	must be identical.
468	Most implementations follow this convention, which simplifies life
469	tremendously.</LI>
470	<LI>The RFC does not specify that the control file and data file job host names
471	must be identical.
472	Most implementations follow this convention, which simplifies life
473	tremendously.</LI>
474	<LI>A zero length data file does not cause a data transfer to take place.
475	LPRng modifies this action to be slightly different.
476	When a zero length data file transfer is indicated,
477	all of the input until the connection is closed is used as the
478	contents of the data file.
479	<P>When 'piping' into the <CODE>lpr</CODE> program,
480	this can be very useful as it eliminates the need to create temporary
481	files on the senders host.
482	The <CODE>lpr -k</CODE> option for details.
483	Note that some print spoolers do not use this interpretation,
484	and this option should be used carefully.
485	</LI>
486	</OL>
487	<H2><A NAME="ss18.5">18.5 Control File Contents</A>
488	</H2>
489
490	<P>The control file consists of a set of lines which either provide
491	printing information or specify data files to be printed.
492	The information lines start with upper case letters or digits,
493	while the data files lines start with lower case letters.
494	Here is a sample control file:
495	<BLOCKQUOTE><CODE>
496	<PRE>
497	Hastart4.astart.com
498	J(stdin)
499	CA
500	Lpapowell
501	Apapowell@astart4+955
502	Ppapowell
503	fdfA955astart4.astart.com
504	N(stdin)
505	UdfA955astart4.astart.com
506	</PRE>
507	</CODE></BLOCKQUOTE>
508	<P>The following are the letters and their meanings in the control file.
509	<CENTER><TABLE BORDER><TR><TD>
510	<BR>
511	X</TD><TD>RFC1179</TD><TD>Meaning</TD></TR><TR><TD>
512	A</TD><TD>LPRng</TD><TD>Identifier for job</TD></TR><TR><TD>
513	C</TD><TD>RFC1179</TD><TD>Class for banner page</TD></TR><TR><TD>
514	H</TD><TD>RFC1179</TD><TD>Host name</TD></TR><TR><TD>
515	I</TD><TD>RFC1179</TD><TD>Indent Printing</TD></TR><TR><TD>
516	J</TD><TD>RFC1179</TD><TD>Job name for banner page</TD></TR><TR><TD>
517	L</TD><TD>RFC1179</TD><TD>Print banner page</TD></TR><TR><TD>
518	M</TD><TD>RFC1179</TD><TD>Mail When Printed</TD></TR><TR><TD>
519	N</TD><TD>RFC1179</TD><TD>Name of source file</TD></TR><TR><TD>
520	P</TD><TD>RFC1179</TD><TD>User identification</TD></TR><TR><TD>
521	Q</TD><TD>LPRng</TD><TD>Queue name</TD></TR><TR><TD>
522	R</TD><TD>LPRng</TD><TD>Accounting info</TD></TR><TR><TD>
523	S</TD><TD>RFC1179</TD><TD>Symbolic link data</TD></TR><TR><TD>
524	T</TD><TD>RFC1179</TD><TD>Title for pr</TD></TR><TR><TD>
525	U</TD><TD>RFC1179</TD><TD>Unlink data file</TD></TR><TR><TD>
526	W</TD><TD>RFC1179</TD><TD>Width of output</TD></TR><TR><TD>
527	Z</TD><TD>LPRng</TD><TD>Filter options</TD></TR><TR><TD>
528	1</TD><TD>RFC1179</TD><TD>troff R font</TD></TR><TR><TD>
529	2</TD><TD>RFC1179</TD><TD>troff I font</TD></TR><TR><TD>
530	3</TD><TD>RFC1179</TD><TD>troff B font</TD></TR><TR><TD>
531	4</TD><TD>RFC1179</TD><TD>troff S font</TD></TR><TR><TD>
532	c</TD><TD>RFC1179</TD><TD>Plot CIF file</TD></TR><TR><TD>
533	d</TD><TD>RFC1179</TD><TD>Print DVI file</TD></TR><TR><TD>
534	f</TD><TD>RFC1179</TD><TD>Print formatted file</TD></TR><TR><TD>
535	g</TD><TD>RFC1179</TD><TD>Plot file</TD></TR><TR><TD>
536	k</TD><TD>RFC1179</TD><TD>Reserved for use by Kerberized LPR clients and servers.</TD></TR><TR><TD>
537	l</TD><TD>RFC1179</TD><TD>Print file leaving control characters</TD></TR><TR><TD>
538	n</TD><TD>RFC1179</TD><TD>Print ditroff output file</TD></TR><TR><TD>
539	o</TD><TD>RFC1179</TD><TD>Print Postscript output file</TD></TR><TR><TD>
540	p</TD><TD>RFC1179</TD><TD>Print file with 'pr' format</TD></TR><TR><TD>
541	t</TD><TD>RFC1179</TD><TD>Print troff output file</TD></TR><TR><TD>
542	v</TD><TD>RFC1179</TD><TD>Print raster file</TD></TR><TR><TD>
543	z</TD><TD>RFC1179</TD><TD>Reserved for future use with the Palladium print system.</TD></TR><TR><TD>
544
545	</TD></TR></TABLE></CENTER>
546	<P>The
547	<CODE>A</CODE> (Identifier)
548	line was introduced to record a unique
549	system wide job identifier for LPRng submitted jobs.
550	This is basically formed from the user name,
551	job number, and host at the time of submission.
552	For example: <CODE>papowell@astart4+955</CODE>
553	is job number 995 submitted by papowell from host astart4.
554	<P>The
555	<CODE>C</CODE> (Class)
556	line is set by the <CODE>lpr -C class</CODE> option,
557	and the value can be used to control printing.
558	For example,
559	the <CODE>lpc class zone </CODE> command would restrict job printing to
560	only jobs with class <CODE>zone</CODE>.
561	<P>The
562	<CODE>H</CODE> (hostname),
563	<CODE>P</CODE> (username),
564	and
565	<CODE>J</CODE> (jobname)
566	fields are used to identify the host and user which sent the job,
567	and to provide information to be displayed by <CODE>lpq</CODE>
568	when reporting job status.
569	<P>The
570	<CODE>L</CODE> (print banner page) field is one that has caused many
571	problems for users.
572	RFC1179 indicates that its presence causes the banner page to be printed,
573	and its absence suppresses banner pages.
574	The <CODE>lpr -h</CODE> option suppresses putting this line into the
575	control file.
576	Usually the <CODE>L</CODE> field is a duplicate of the <CODE>P</CODE>
577	field.
578	<P>The <CODE>M</CODE> (mail information)
579	field supplies a mail address for LPRng to send mail to when
580	a job is completed.
581	See
582	<A HREF="LPRng-HOWTO-17.html#mail">LPR -m and user logging</A>
583	for more details.
584	<P>The <CODE>N</CODE> (file name) field is usually provided to identify
585	the file name corresponding to the data file.
586	This can be used to print names on page separators, etc.
587	LPRng largely ignores this line.
588	<P>The
589	<CODE>I</CODE> (indent)
590	and
591	<CODE>W</CODE> (width)
592	fields are supposed to specify a page indent and width for printing.
593	These fields are passed to filters if they are present.
594	<P>The <CODE>Q</CODE> (queue name)
595	field is an LPRng extension,
596	and contains the name of the print queue the job was originally sent to.
597	See
598	<A HREF="LPRng-HOWTO-11.html#qq">qq printcap option</A> for details.
599	<P>The <CODE>R</CODE> (accounting info) field was added by LPRng to allow
600	a specified account to be billed for job printing.
601	The <CODE>lpr -Rname</CODE> option can be used to specify the accounting name.
602	<P>The
603	<CODE>S</CODE> (symbolic link)
604	and
605	<CODE>U</CODE> (unlink after printing)
606	lines were used by the original BSD LPD print system to control
607	how it passed files to the print server.
608	LPRng ignores these lines.
609	In fact, it will remove <CODE>S</CODE> lines and force the <CODE>U</CODE>
610	lines to refer only to job data files.
611	This closes a nasty security loophole on non-LPRng print spoolers.
612	<P>The <CODE>T</CODE> (pr job title) is used with the <CODE>lpr -p</CODE>
613	operation to supply a banner to the <CODE>pr</CODE> program.
614	<P>The <CODE>Z</CODE> (filter options) value is specified with
615	<CODE>lpr -Zoption</CODE> and is passed to the data file filters
616	during the printing operation.
617	See
618	<A HREF="LPRng-HOWTO-13.html#secfilter">Filters</A> for details on how the
619	this is used during the printing process.
620	<P>All of the lower case letters are reserved for format specifications for
621	data files.
622	In the control file, these are followed by the name of the data file
623	to which they correspond.
624	While in principle different data files in the control file can have
625	different formats,
626	this has not been implemented in any known spooling system.
627	See
628	<A HREF="LPRng-HOWTO-13.html#secfilter">Filters</A> for details on how the
629	data file formats are used during the printing process.
630	<H2><A NAME="ss18.6">18.6 LPQ Requests</A>
631	</H2>
632
633	<P>The RFC1179 protocol specifies that <CODE>lpq</CODE> print status
634	requests can be sent to the <CODE>lpd</CODE> server.
635	The lpq requests have the format:
636	<BLOCKQUOTE><CODE>
637	<PRE>
638	\003printer [id]* \n short
639	\004printer [id]* \n long
640	\009printer [id]* \n LPRng extension- verbose
641	</PRE>
642	</CODE></BLOCKQUOTE>
643	<P>The <CODE>lpd</CODE> print server will then return queue status
644	and close the data connection.
645	<P>RFC1179 does not state in any manner what the format of the queue status
646	should be.
647	Thus, implementors have been free to augment or change the status as
648	they like.
649	Even the BSD LPR status format has been changed from different versions.
650	<P>See
651	<A HREF="LPRng-HOWTO-17.html#statusref">Status Monitoring and Logging</A>
652	for information on the formats returned.
653	<P>The <CODE>id</CODE> values are used to select the jobs to be displayed.
654	LPRng displays any job whose ID, hostname, or user name information
655	from the control file
656	<CODE>A</CODE>,
657	<CODE>H</CODE>,
658	or
659	<CODE>P</CODE> fields match any of the id values.
660	<P>Note that since there is no identification of the information requestor,
661	then restriction of information is almost impossible.
662	<P>
663	<H2><A NAME="ss18.7">18.7 LPRM Requests</A>
664	</H2>
665
666	<P>The RFC1179 protocol specifies that <CODE>lprm</CODE> job removal
667	requests can be sent to the <CODE>lpd</CODE> server.
668	The lpq requests have the format:
669	<BLOCKQUOTE><CODE>
670	<PRE>
671	\005printer user [id]* \n
672	</PRE>
673	</CODE></BLOCKQUOTE>
674	<P>The <CODE>lpd</CODE> print server will search the specified print queue
675	and remove any job whose ID, hostname, or user name information
676	from the control file
677	<CODE>A</CODE>,
678	<CODE>H</CODE>,
679	or
680	<CODE>P</CODE> fields match any of the id values
681	and for which the user has permission to perform a removal operation.
682	See the
683	<A HREF="LPRng-HOWTO-14.html#lpdpermsref">/etc/lpd.perms</A> file for details on
684	permissions.
685	<P>Most RFC1179 compatible spoolers use the user information in the
686	request as the name of the user which spooled the job.
687	However,
688	in a network environment this is extremely easy to fabricate,
689	and is at best a weak type of authentication.
690	<H2><A NAME="lpcreread"></A> <A NAME="ss18.8">18.8 LPC Requests</A>
691	</H2>
692
693	<P>LPRng has extended the RFC1179 protocol to allow queue and printer control
694	commands to be sent to the LPD server.
695	The format of these commands are:
696	<P>
697	<BLOCKQUOTE><CODE>
698	<PRE>
699	\006printer user key [options]
700	</PRE>
701	</CODE></BLOCKQUOTE>
702	<P>The following commands are supported.
703	<CENTER><TABLE BORDER><TR><TD>
704	<BR>
705	Command</TD><TD>Operation</TD></TR><TR><TD>
706	<CODE> active [printer[@host]]</CODE></TD><TD>check to see if server accepting connections</TD></TR><TR><TD>
707	<CODE> abort (printer[@host] \| all) </CODE></TD><TD>terminate server process printing job</TD></TR><TR><TD>
708	<CODE> disable (printer[@host] \| all) </CODE></TD><TD>disable queueing</TD></TR><TR><TD>
709	<CODE> debug (printer[@host] \| all) debugparms </CODE></TD><TD>set debug level for printer</TD></TR><TR><TD>
710	<CODE> enable (printer[@host] \| all) </CODE></TD><TD>enable queueing</TD></TR><TR><TD>
711	<CODE> hold (printer[@host] \| all) (name[@host] \| job \| all)* </CODE></TD><TD>hold job</TD></TR><TR><TD>
712	<CODE> holdall (printer[@host] \| all) </CODE></TD><TD>hold all jobs on</TD></TR><TR><TD>
713	<CODE> kill (printer[@host] \| all) </CODE></TD><TD>stop and restart server</TD></TR><TR><TD>
714	<CODE> lpd [printer[@host]] </CODE></TD><TD>get LPD PID for server</TD></TR><TR><TD>
715	<CODE> lpq (printer[@host] \| all) (name[@host] \| job \| all)* </CODE></TD><TD>invoke LPQ</TD></TR><TR><TD>
716	<CODE> lprm (printer[@host] \| all) (name[@host]\|host\|job\| all)* </CODE></TD><TD>invoke LPRM</TD></TR><TR><TD>
717	<CODE> move printer (user\|jobid)* target </CODE></TD><TD>move jobs to new queue</TD></TR><TR><TD>
718	<CODE> noholdall (printer[@host] \| all) </CODE></TD><TD>hold all jobs off</TD></TR><TR><TD>
719	<CODE> printcap (printer[@host] \| all) </CODE></TD><TD>report printcap values</TD></TR><TR><TD>
720	<CODE> quit </CODE></TD><TD>exit LPC</TD></TR><TR><TD>
721	<CODE> redirect (printer[@host] \| all) (printer@host \| off )* </CODE></TD><TD>redirect jobs</TD></TR><TR><TD>
722	<CODE> release (printer[@host] \| all) (name[@host] \| job \| all)* </CODE></TD><TD>release job</TD></TR><TR><TD>
723	<CODE> reread [printer[@host]]</CODE></TD><TD>LPD reread database information</TD></TR><TR><TD>
724	<CODE> start (printer[@host] \| all) </CODE></TD><TD>start printing</TD></TR><TR><TD>
725	<CODE> status (printer[@host] \| all) </CODE></TD><TD>status of printers</TD></TR><TR><TD>
726	<CODE> stop (printer[@host] \| all) </CODE></TD><TD>stop printing</TD></TR><TR><TD>
727	<CODE> topq (printer[@host] \| all) (name[@host] \| job \| all)* </CODE></TD><TD>reorder job</TD></TR><TR><TD>
728	<CODE> defaultq </CODE></TD><TD>default queue for LPD server</TD></TR><TR><TD>
729	<CODE> local (printer \| all) </CODE></TD><TD>client printcap and configuration information</TD></TR><TR><TD>
730	<CODE> server (printer \| all) </CODE></TD><TD>server printcap and configuration information</TD></TR><TR><TD>
731
732	</TD></TR></TABLE></CENTER>
733	<P>Many of these commands support extremely specialized operations for
734	print queue management,
735	However, the following are the most commonly used and are supported by
736	the BSD LPD print spooling system as well:
737	<UL>
738	<LI><CODE> start, stop, enable, disable </CODE><BR>
739	Start and stop will start and stop printing for a specified queue.
740	Enable and disable enable and disable sending and/or accepting jobs
741	for the queue.</LI>
742	<LI><CODE> abort, kill </CODE><BR>
743	Abort will cause the process doing the actual job printing to be terminated.
744	Kill does an abort, and then restarts the printing process.
745	These commands are used to restart a queue printing after some disaster.</LI>
746	<LI><CODE> topq </CODE>
747	Places selected jobs at the top of the print queue.</LI>
748	<LI><CODE> status </CODE><BR>
749	Shows a status display of the print spools on the server.</LI>
750	</UL>
751	<P>The following commands are extensions to the basic set provided by the
752	BSD LPD system.
753	<UL>
754	<LI><CODE> lpq, lprm </CODE><BR>
755	Invokes the lpq or lprm program from lpc.
756	Useful when in the interactive mode.</LI>
757	<LI><CODE> hold, holdall, release </CODE><BR>
758	The hold command will cause the selected jobs to be held until
759	released.
760	The holdall jobs sets all jobs submitted to the queue to be held until
761	released.
762	The release command releases jobs for printing.
763	If a job has had an error and is in the error state,
764	the release command will cause it to be reprinted.</LI>
765	<LI><CODE> move, redirect </CODE><BR>
766	The move command will move selected jobs to the specified spool queue.
767	The redirect command sends all jobs submitted to the queue to be
768	sent to the specified queue.</LI>
769	<LI><CODE> active, lpd, reread </CODE><BR>
770	The active command will connect to the server for the printer.
771	This is used to check to see if non-LPRng print servers are active.
772	The lpd command will connect to the server and
773	get the process id (PID) of the <CODE>lpd</CODE> server.
774	The reread command causes a SIGHUP signal to be sent to the lpd process,
775	causing it to reread the
776	<CODE>/etc/lpd.conf</CODE>,
777	<CODE>/etc/printcap</CODE>,
778	or
779	<CODE>/etc/lpd.perms</CODE> files.
780	This is usually done when some important configuration information has
781	been modified and the administrator wants to have the server use the
782	new information.</LI>
783	<LI><CODE> debug </CODE><BR>
784	This is a desperation facility for developers that allows dynamic enabling
785	of debug information generation.
786	Not normally used in general operation.</LI>
787	<LI><CODE> local, server </CODE><BR>
788	These commands will print out the configuration information in the
789	local
790	<CODE>/etc/lpd.conf</CODE> file,
791	as well as the printcap information for the specified printers;
792	<CODE>local</CODE>
793	prints what the LPRng clients (<CODE>lpr, lpq, ...</CODE>) would use
794	while
795	<CODE>server</CODE>
796	prints what the LPRng server (<CODE>lpd</CODE>) would use if running on this host.
797	This is an extremely useful diagnostic tool for administrators.
798	Not normally used in general operation.</LI>
799	</UL>
800	<H2><A NAME="blocktransfer"></A> <A NAME="sendblockformat"></A> <A NAME="ss18.9">18.9 Block Job Transfer</A>
801	</H2>
802
803	<P>Options used:
804	<UL>
805	<LI> <CODE>send_block_format</CODE><EM>  Transfer job as a block</EM></LI>
806	</UL>
807	<P>In normal job transfer operations,
808	the sender and receiver have a handshake interaction in order to transfer
809	a print job.
810	Each file is sent individually.
811	The <CODE>send_block_format</CODE> option forces
812	a Block Job Transfer operation.
813	This causes the sender to transfer a single file containing all the
814	job printing information,
815	including control file and data files.
816	<P>The transfer command line has the form:
817	<BLOCKQUOTE><CODE>
818	<PRE>
819	\007printer size\n
820	</PRE>
821	</CODE></BLOCKQUOTE>
822	<P>The receiver will return any acknowledgement of a single 0 octet,
823	and then the size bytes of the job will be transferred by the sender.
824	At the end of the transfer a single 0 octet is added,
825	and the receiver will indicate success by returning a single 0 octet.
826	Any other value returned by the receiver indicates an error condition.
827	<P>The file transferred by the sender is simply the command lines that it
828	would have normally sent for job transfer,
829	followed by the control or data file values.
830	<H2><A NAME="ss18.10">18.10 Authenticated Transfer</A>
831	</H2>
832
833	<P>RFC1179 does not provide any authentication or encryption mechanism
834	for the transfer of jobs or commands to the <CODE>lpd</CODE>
835	print server.
836	The Authenticated Transfer operation was added to allow an encrypted
837	or authenticated transfer of print jobs or commands.
838	<P>Since there are various restrictions on the incorporation of authentication
839	facilities into programs,
840	LPRng supports authentication by providing a simple interface to
841	encryption programs.
842	<P>The idea is that when authentication is required when sending a job,
843	LPRng will generate a block transfer job as described for the
844	<A HREF="#blocktransfer">Block Transfer operation,</A>
845	and then invoke a set of programs to encryt and transfer the file,
846	and encrypt and transfer the returned status.
847	<P>Similarly,
848	when sending a command,
849	the command information will be placed in a file
850	and the encrypted file will be transferred.
851	<P>This technique means that the programs and support to do encryption
852	are external to LPRng,
853	and can use any type of method that they choose to implement the
854	secure and/or authenticated transfer.
855	<P>See
856	<A HREF="LPRng-HOWTO-16.html#authref">Authentication and Encryption</A>
857	for details on the authentication interface.
858	<HR>
859	<A HREF="LPRng-HOWTO-19.html">Next</A>
860	<A HREF="LPRng-HOWTO-17.html">Previous</A>
861	<A HREF="LPRng-HOWTO.html#toc18">Contents</A>
862	</BODY>
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