Keywords: LPDP
Network Printing Working Group L. McLaughlin III, Editor
Request for Comments: 1179 The Wollongong Group
August 1990
Line Printer Daemon Protocol
Status of this Memo
This RFC describes an existing print server protocol widely used on
the Internet for communicating between line printer daemons (both
clients and servers). This memo is for informational purposes only,
and does not specify an Internet standard. Please refer to the
current edition of the "IAB Official Protocol Standards" for the
standardization state and status of this protocol. Distribution of
this memo is unlimited.
1. Introduction
The Berkeley versions of the Unix(tm) operating system provide line
printer spooling with a collection of programs: lpr (assign to
queue), lpq (display the queue), lprm (remove from queue), and lpc
(control the queue). These programs interact with an autonomous
process called the line printer daemon. This RFC describes the
protocols with which a line printer daemon client may control
printing.
This memo is based almost entirely on the work of Robert Knight at
Princeton University. I gratefully acknowledge his efforts in
deciphering the UNIX lpr protocol and producing earlier versions of
this document.
2. Model of Printing Environment
A group of hosts request services from a line printer daemon process
running on a host. The services provided by the process are related
to printing jobs. A printing job produces output from one file.
Each job will have a unique job number which is between 0 and 999,
inclusive. The jobs are requested by users which have names. These
user names may not start with a digit.
3. Specification of the Protocol
The specification includes file formats for the control and data
files as well as messages used by the protocol.
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3.1 Message formats
LPR is a a TCP-based protocol. The port on which a line printer
daemon listens is 515. The source port must be in the range 721 to
731, inclusive. A line printer daemon responds to commands send to
its port. All commands begin with a single octet code, which is a
binary number which represents the requested function. The code is
immediately followed by the ASCII name of the printer queue name on
which the function is to be performed. If there are other operands
to the command, they are separated from the printer queue name with
white space (ASCII space, horizontal tab, vertical tab, and form
feed). The end of the command is indicated with an ASCII line feed
character.
4. Diagram Conventions
The diagrams in the rest of this RFC use these conventions. These
diagrams show the format of an octet stream sent to the server. The
outermost box represents this stream. Each box within the outermost
one shows one portion of the stream. If the contents of the box is
two decimal digits, this indicates that the binary 8 bit value is to
be used. If the contents is two uppercase letters, this indicates
that the corresponding ASCII control character is to be used. An
exception to this is that the character SP can be interpreted as
white space. (See the preceding section for a definition.) If the
contents is a single letter, the ASCII code for this letter must be
sent. Otherwise, the contents are intended to be mnemonic of the
contents of the field which is a sequence of octets.
5. Daemon commands
The verbs in the command names should be interpreted as statements
made to the daemon. Thus, the command "Print any waiting jobs" is an
imperative to the line printer daemon to which it is sent. A new
connection must be made for each command to be given to the daemon.
5.1 01 - Print any waiting jobs
+----+-------+----+
| 01 | Queue | LF |
+----+-------+----+
Command code - 1
Operand - Printer queue name
This command starts the printing process if it not already running.
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5.2 02 - Receive a printer job
+----+-------+----+
| 02 | Queue | LF |
+----+-------+----+
Command code - 2
Operand - Printer queue name
Receiving a job is controlled by a second level of commands. The
daemon is given commands by sending them over the same connection.
The commands are described in the next section (6).
After this command is sent, the client must read an acknowledgement
octet from the daemon. A positive acknowledgement is an octet of
zero bits. A negative acknowledgement is an octet of any other
pattern.
5.3 03 - Send queue state (short)
+----+-------+----+------+----+
| 03 | Queue | SP | List | LF |
+----+-------+----+------+----+
Command code - 3
Operand 1 - Printer queue name
Other operands - User names or job numbers
If the user names or job numbers or both are supplied then only those
jobs for those users or with those numbers will be sent.
The response is an ASCII stream which describes the printer queue.
The stream continues until the connection closes. Ends of lines are
indicated with ASCII LF control characters. The lines may also
contain ASCII HT control characters.
5.4 04 - Send queue state (long)
+----+-------+----+------+----+
| 04 | Queue | SP | List | LF |
+----+-------+----+------+----+
Command code - 4
Operand 1 - Printer queue name
Other operands - User names or job numbers
If the user names or job numbers or both are supplied then only those
jobs for those users or with those numbers will be sent.
The response is an ASCII stream which describes the printer queue.
The stream continues until the connection closes. Ends of lines are
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indicated with ASCII LF control characters. The lines may also
contain ASCII HT control characters.
5.5 05 - Remove jobs
+----+-------+----+-------+----+------+----+
| 05 | Queue | SP | Agent | SP | List | LF |
+----+-------+----+-------+----+------+----+
Command code - 5
Operand 1 - Printer queue name
Operand 2 - User name making request (the agent)
Other operands - User names or job numbers
This command deletes the print jobs from the specified queue which
are listed as the other operands. If only the agent is given, the
command is to delete the currently active job. Unless the agent is
"root", it is not possible to delete a job which is not owned by the
user. This is also the case for specifying user names instead of
numbers. That is, agent "root" can delete jobs by user name but no
other agents can.
6. Receive job subcommands
These commands are processed when the line printer daemon has
been given the receive job command. The daemon will continue to
process commands until the connection is closed.
After a subcommand is sent, the client must wait for an
acknowledgement from the daemon. A positive acknowledgement is an
octet of zero bits. A negative acknowledgement is an octet of any
other pattern.
LPR clients SHOULD be able to sent the receive data file and receive
control file subcommands in either order. LPR servers MUST be able
to receive the control file subcommand first and SHOULD be able to
receive the data file subcommand first.
6.1 01 - Abort job
Command code - 1
+----+----+
| 01 | LF |
+----+----+
No operands should be supplied. This subcommand will remove any
files which have been created during this "Receive job" command.
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6.2 02 - Receive control file
+----+-------+----+------+----+
| 02 | Count | SP | Name | LF |
+----+-------+----+------+----+
Command code - 2
Operand 1 - Number of bytes in control file
Operand 2 - Name of control file
The control file must be an ASCII stream with the ends of lines
indicated by ASCII LF. The total number of bytes in the stream is
sent as the first operand. The name of the control file is sent as
the second. It should start with ASCII "cfA", followed by a three
digit job number, followed by the host name which has constructed the
control file. Acknowledgement processing must occur as usual after
the command is sent.
The next "Operand 1" octets over the same TCP connection are the
intended contents of the control file. Once all of the contents have
been delivered, an octet of zero bits is sent as an indication that
the file being sent is complete. A second level of acknowledgement
processing must occur at this point.
6.3 03 - Receive data file
+----+-------+----+------+----+
| 03 | Count | SP | Name | LF |
+----+-------+----+------+----+
Command code - 3
Operand 1 - Number of bytes in data file
Operand 2 - Name of data file
The data file may contain any 8 bit values at all. The total number
of bytes in the stream may be sent as the first operand, otherwise
the field should be cleared to 0. The name of the data file should
start with ASCII "dfA". This should be followed by a three digit job
number. The job number should be followed by the host name which has
constructed the data file. Interpretation of the contents of the
data file is determined by the contents of the corresponding control
file. If a data file length has been specified, the next "Operand 1"
octets over the same TCP connection are the intended contents of the
data file. In this case, once all of the contents have been
delivered, an octet of zero bits is sent as an indication that the
file being sent is complete. A second level of acknowledgement
processing must occur at this point.
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7. Control file lines
This section discusses the format of the lines in the control file
which is sent to the line printer daemon.
Each line of the control file consists of a single, printable ASCII
character which represents a function to be performed when the file
is printed. Interpretation of these command characters are case-
sensitive. The rest of the line after the command character is the
command's operand. No leading white space is permitted after the
command character. The line ends with an ASCII new line.
Those commands which have a lower case letter as a command code are
used to specify an actual printing request. The commands which use
upper case are used to describe parametric values or background
conditions.
Some commands must be included in every control file. These are 'H'
(responsible host) and 'P' (responsible user). Additionally, there
must be at least one lower case command to produce any output.
7.1 C - Class for banner page
+---+-------+----+
| C | Class | LF |
+---+-------+----+
Command code - 'C'
Operand - Name of class for banner pages
This command sets the class name to be printed on the banner page.
The name must be 31 or fewer octets. The name can be omitted. If it
is, the name of the host on which the file is printed will be used.
The class is conventionally used to display the host from which the
printing job originated. It will be ignored unless the print banner
command ('L') is also used.
7.2 H - Host name
+---+------+----+
| H | Host | LF |
+---+------+----+
Command code - 'H'
Operand - Name of host
This command specifies the name of the host which is to be treated as
the source of the print job. The command must be included in the
control file. The name of the host must be 31 or fewer octets.
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7.3 I - Indent Printing
+---+-------+----+
| I | count | LF |
+---+-------+----+
Command code - 'I'
Operand - Indenting count
This command specifies that, for files which are printed with the
'f', of columns given. (It is ignored for other output generating
commands.) The identing count operand must be all decimal digits.
7.4 J - Job name for banner page
+---+----------+----+
| J | Job name | LF |
+---+----------+----+
Command code - 'J'
Operand - Job name
This command sets the job name to be printed on the banner page. The
name of the job must be 99 or fewer octets. It can be omitted. The
job name is conventionally used to display the name of the file or
files which were "printed". It will be ignored unless the print
banner command ('L') is also used.
7.5 L - Print banner page
+---+------+----+
| L | User | LF |
+---+------+----+
Command code - 'L'
Operand - Name of user for burst pages
This command causes the banner page to be printed. The user name can
be omitted. The class name for banner page and job name for banner
page commands must precede this command in the control file to be
effective.
7.6 M - Mail When Printed
+---+------+----+
| M | user | LF |
+---+------+----+
Command code - 'M'
Operand - User name
This entry causes mail to be sent to the user given as the operand at
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the host specified by the 'H' entry when the printing operation ends
(successfully or unsuccessfully).
7.7 N - Name of source file
+---+------+----+
| N | Name | LF |
+---+------+----+
Command code - 'N'
Operand - File name
This command specifies the name of the file from which the data file
was constructed. It is returned on a query and used in printing with
the 'p' command when no title has been given. It must be 131 or
fewer octets.
7.8 P - User identification
+---+------+----+
| P | Name | LF |
+---+------+----+
Command code - 'P'
Operand - User id
This command specifies the user identification of the entity
requesting the printing job. This command must be included in the
control file. The user identification must be 31 or fewer octets.
7.9 S - Symbolic link data
+---+--------+----+-------+----+
| S | device | SP | inode | LF |
+---+--------+----+-------+----+
Command code - 'S'
Operand 1 - Device number
Operand 2 - Inode number
This command is used to record symbolic link data on a Unix system so
that changing a file's directory entry after a file is printed will
not print the new file. It is ignored if the data file is not
symbolically linked.
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7.10 T - Title for pr
+---+-------+----+
| T | title | LF |
+---+-------+----+
Command code - 'T'
Operand - Title text
This command provides a title for a file which is to be printed with
either the 'p' command. (It is ignored by all of the other printing
commands.) The title must be 79 or fewer octets.
7.11 U - Unlink data file
+---+------+----+
| U | file | LF |
+---+------+----+
Command code - 'U'
Operand - File to unlink
This command indicates that the specified file is no longer needed.
This should only be used for data files.
7.12 W - Width of output
+---+-------+----+
| W | width | LF |
+---+-------+----+
Command code - 'W'
Operand - Width count
This command limits the output to the specified number of columns for
the 'f', 'l', and 'p' commands. (It is ignored for other output
generating commands.) The width count operand must be all decimal
digits. It may be silently reduced to some lower value. The default
value for the width is 132.
7.13 1 - troff R font
+---+------+----+
| 1 | file | LF |
+---+------+----+
Command code - '1'
Operand - File name
This command specifies the file name for the troff R font. [1] This
is the font which is printed using Times Roman by default.
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7.14 2 - troff I font
+---+------+----+
| 2 | file | LF |
+---+------+----+
Command code - '2'
Operand - File name
This command specifies the file name for the troff I font. [1] This
is the font which is printed using Times Italic by default.
7.15 3 - troff B font
+---+------+----+
| 3 | file | LF |
+---+------+----+
Command code - '3'
Operand - File name
This command specifies the file name for the troff B font. [1] This
is the font which is printed using Times Bold by default.
7.16 4 - troff S font
+---+------+----+
| 4 | file | LF |
+---+------+----+
Command code - '4'
Operand - File name
This command specifies the file name for the troff S font. [1] This
is the font which is printed using Special Mathematical Font by
default.
7.17 c - Plot CIF file
+---+------+----+
| c | file | LF |
+---+------+----+
Command code - 'c'
Operand - File to plot
This command causes the data file to be plotted, treating the data as
CIF (CalTech Intermediate Form) graphics language. [2]
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7.18 d - Print DVI file
+---+------+----+
| d | file | LF |
+---+------+----+
Command code - 'd'
Operand - File to print
This command causes the data file to be printed, treating the data as
DVI (TeX output). [3]
7.19 f - Print formatted file
+---+------+----+
| f | file | LF |
+---+------+----+
Command code - 'f'
Operand - File to print
This command cause the data file to be printed as a plain text file,
providing page breaks as necessary. Any ASCII control characters
which are not in the following list are discarded: HT, CR, FF, LF,
and BS.
7.20 g - Plot file
+---+------+----+
| g | file | LF |
+---+------+----+
Command code - 'g'
Operand - File to plot
This command causes the data file to be plotted, treating the data as
output from the Berkeley Unix plot library. [1]
7.21 k - Reserved for use by Kerberized LPR clients and servers.
7.22 l - Print file leaving control characters
+---+------+----+
| l | file | LF |
+---+------+----+
Command code - 'l' (lower case L)
Operand - File to print
This command causes the specified data file to printed without
filtering the control characters (as is done with the 'f' command).
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7.23 n - Print ditroff output file
+---+------+----+
| n | file | LF |
+---+------+----+
Command code - 'n'
Operand - File to print
This command prints the data file to be printed, treating the data as
ditroff output. [4]
7.24 o - Print Postscript output file
+---+------+----+
| o | file | LF |
+---+------+----+
Command code - 'o'
Operand - File to print
This command prints the data file to be printed, treating the data as
standard Postscript input.
7.25 p - Print file with 'pr' format
+---+------+----+
| p | file | LF |
+---+------+----+
Command code - 'p'
Operand - File to print
This command causes the data file to be printed with a heading, page
numbers, and pagination. The heading should include the date and
time that printing was started, the title, and a page number
identifier followed by the page number. The title is the name of
file as specified by the 'N' command, unless the 'T' command (title)
has been given. After a page of text has been printed, a new page is
started with a new page number. (There is no way to specify the
length of the page.)
7.26 r - File to print with FORTRAN carriage control
+---+------+----+
| r | file | LF |
+---+------+----+
Command code - 'r'
Operand - File to print
This command causes the data file to be printed, interpreting the
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first column of each line as FORTRAN carriage control. The FORTRAN
standard limits this to blank, "1", "0", and "+" carriage controls.
Most FORTRAN programmers also expect "-" (triple space) to work as
well.
7.27 t - Print troff output file
+---+------+----+
| t | file | LF |
+---+------+----+
Command code - 't'
Operand - File to print
This command prints the data file as Graphic Systems C/A/T
phototypesetter input. [5] This is the standard output of the Unix
"troff" command.
7.28 v - Print raster file
+---+------+----+
| v | file | LF |
+---+------+----+
Command code - 'v'
Operand - File to print
This command prints a Sun raster format file. [6]
7.29 z - Reserved for future use with the Palladium print system.
REFERENCES and BIBLIOGRAPHY
[1] Computer Science Research Group, "UNIX Programmer's Reference
Manual", USENIX, 1986.
[2] Hon and Sequin, "A Guide to LSI Implementation", XEROX PARC,
1980.
[3] Knuth, D., "TeX The Program".
[4] Kernighan, B., "A Typesetter-independent TROFF".
[5] "Model C/A/T Phototypesetter", Graphic Systems, Inc. Hudson, N.H.
[6] Sun Microsystems, "Pixrect Reference Manual", Sun Microsystems,
Mountain View, CA, 1988.
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Security Considerations
Security issues are not discussed in this memo.
Author's Address
Leo J. McLaughlin III
The Wollongong Group
1129 San Antonio Road
Palo Alto, CA 94303
Phone: 415-962-7100
EMail: ljm@twg.com
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