[thirdparty/cups.git] / doc / help / man-backend.html

<!DOCTYPE html>
<html>
  <head>
    <meta name="creator" content="mantohtml v2.0.2">
    <title>backend(7)</title>
  </head>
  <body>
    <h1 id="backend-7">backend(7)</h1>
    <h2 id="backend-7.name">Name</h2>
<p>backend - cups backend transmission interfaces
</p>
    <h2 id="backend-7.synopsis">Synopsis</h2>
<p><strong>backend</strong>
<br>
<strong>backend</strong>
<em>job</em>
<em>user</em>
<em>title</em>
<em>num-copies</em>
<em>options</em>
[
<em>filename</em>
]
</p>
    <pre>
<strong>#include &lt;cups/cups.h></strong>

<strong>const char *cupsBackendDeviceURI</strong>(<strong>char **</strong><em>argv</em>);

<strong>void cupsBackendReport</strong>(<strong>const char *</strong><em>device_scheme</em>,
                       <strong>const char *</strong><em>device_uri</em>,
                       <strong>const char *</strong><em>device_make_and_model</em>,
                       <strong>const char *</strong><em>device_info</em>,
                       <strong>const char *</strong><em>device_id</em>,
                       <strong>const char *</strong><em>device_location</em>);

<strong>ssize_t cupsBackChannelWrite</strong>(<strong>const char *</strong><em>buffer</em>,
                             <strong>size_t </strong><em>bytes</em>, <strong>double </strong><em>timeout</em>);

<strong>int cupsSideChannelRead</strong>(<strong>cups_sc_command_t *</strong><em>command</em>,
                        <strong>cups_sc_status_t *</strong><em>status</em>, <strong>char *</strong><em>data</em>,
                        <strong>int *</strong><em>datalen</em>, <strong>double </strong><em>timeout</em>);

<strong>int cupsSideChannelWrite</strong>(<strong>cups_sc_command_t </strong><em>command</em>,
                         <strong>cups_sc_status_t </strong><em>status</em>, <strong>const char *</strong><em>data</em>,
                         <strong>int </strong><em>datalen</em>, <strong>double </strong><em>timeout</em>);
</pre>
    <h2 id="backend-7.description">Description</h2>
<p>Backends are a special type of
<a href="filter.html"><strong>filter</strong>(7)</a>

which is used to send print data to and discover different devices on the system.
</p>
    <p>Like filters, backends must be capable of reading from a filename on the command-line or from the standard input, copying the standard input to a temporary file as required by the physical interface.
</p>
    <p>The command name (<em>argv[0]</em>) is set to the device URI of the destination printer.
Authentication information in
<em>argv[0]</em>
is removed, so backend developers are urged to use the
<strong>DEVICE_URI</strong>
environment variable whenever authentication information is required. The
<strong>cupsBackendDeviceURI</strong>()

function may be used to retrieve the correct device URI.
</p>
    <p>Back-channel data from the device should be relayed to the job filters using the <em>cupsBackChannelWrite</em> function.
</p>
    <p>Backends are responsible for reading side-channel requests using the
<strong>cupsSideChannelRead</strong>()

function and responding with the
<strong>cupsSideChannelWrite</strong>()

function. The
<strong>CUPS_SC_FD</strong>
constant defines the file descriptor that should be monitored for incoming requests.
</p>
    <h3 id="backend-7.description.device-discovery">Device Discovery</h3>
<p>When run with no arguments, the backend should list the devices and schemes it supports or is advertising to the standard output.
The output consists of zero or more lines consisting of any of the following forms:
</p>
    <pre>
    device-class scheme &quot;Unknown&quot; &quot;device-info&quot;
    device-class device-uri &quot;device-make-and-model&quot; &quot;device-info&quot;
    device-class device-uri &quot;device-make-and-model&quot; &quot;device-info&quot; &quot;device-id&quot;
    device-class device-uri &quot;device-make-and-model&quot; &quot;device-info&quot; &quot;device-id&quot; &quot;device-location&quot;
</pre>
    <p>The
<strong>cupsBackendReport</strong>()

function can be used to generate these lines and handle any necessary escaping of characters in the various strings.
</p>
    <p>The
<em>device-class</em>
field is one of the following values:
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>direct</strong><br>
The device-uri refers to a specific direct-access device with no options, such as a parallel, USB, or SCSI device.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>file</strong><br>
The device-uri refers to a file on disk.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>network</strong><br>
The device-uri refers to a networked device and conforms to the general form for
network URIs.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>serial</strong><br>
The device-uri refers to a serial device with configurable baud rate and other options.
If the device-uri contains a baud value, it represents the maximum baud rate supported by the device.
</p>
    <p>The
<em>scheme</em>
field provides the URI scheme that is supported by the backend.
Backends should use this form only when the backend supports any URI using that scheme.
The
<em>device-uri</em>
field specifies the full URI to use when communicating with the device.
</p>
    <p>The
<em>device-make-and-model</em>
field specifies the make and model of the device, e.g. &quot;Example Foojet 2000&quot;.
If the make and model is not known, you must report &quot;Unknown&quot;.
</p>
    <p>The
<em>device-info</em>
field specifies additional information about the device.
Typically this includes the make and model along with the port number or network address, e.g. &quot;Example Foojet 2000 USB #1&quot;.
</p>
    <p>The optional
<em>device-id</em>
field specifies the IEEE-1284 device ID string for the device, which is used to select a matching driver.
</p>
    <p>The optional
<em>device-location</em>
field specifies the physical location of the device, which is often used to pre-populate the printer-location attribute when adding a printer.
</p>
    <h3 id="backend-7.description.permissions">Permissions</h3>
<p>Backends without world read and execute permissions are run as the root user.
Otherwise, the backend is run using an unprivileged user account, typically &quot;lp&quot;.
</p>
    <h2 id="backend-7.exit-status">Exit Status</h2>
<p>The following exit codes are defined for backends:
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_OK</strong><br>
The print file was successfully transmitted to the device or remote server.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_FAILED</strong><br>
<br>
The print file was not successfully transmitted to the device or remote server.
The scheduler will respond to this by canceling the job, retrying the job, or stopping the queue depending on the state of the
<em>printer-error-policy</em>
attribute.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_AUTH_REQUIRED</strong><br>
The print file was not successfully transmitted because valid authentication information is required.
The scheduler will respond to this by holding the job and adding the 'cups-held-for-authentication' keyword to the &quot;job-reasons&quot; Job Description attribute.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_HOLD</strong><br>
The print file was not successfully transmitted because it cannot be printed at this time.
The scheduler will respond to this by holding the job.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_STOP</strong><br>
The print file was not successfully transmitted because it cannot be printed at this time.
The scheduler will respond to this by stopping the queue.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_CANCEL</strong><br>
The print file was not successfully transmitted because one or more attributes are not supported or the job was canceled at the printer.
The scheduler will respond to this by canceling the job.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_RETRY</strong><br>
The print file was not successfully transmitted because of a temporary issue.
The scheduler will retry the job at a future time - other jobs may print before this one.
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_RETRY_CURRENT</strong><br>
The print file was not successfully transmitted because of a temporary issue.
The scheduler will retry the job immediately without allowing intervening jobs.
</p>
    <p>All other exit code values are reserved.
</p>
    <h2 id="backend-7.environment">Environment</h2>
<p>In addition to the environment variables listed in
<a href="cups.html"><strong>cups</strong>(1)</a>

and
<a href="filter.html"><strong>filter</strong>(7),</a>

CUPS backends can expect the following environment variable:
</p>
    <p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>DEVICE_URI</strong><br>
The device URI associated with the printer.
</p>
    <h2 id="backend-7.files">Files</h2>
<p><em>/etc/cups/cups-files.conf</em>
</p>
    <h2 id="backend-7.notes">Notes</h2>
<p>CUPS backends are not generally designed to be run directly by the user.
Aside from the device URI issue (
<em>argv[0]</em>
and
<strong>DEVICE_URI</strong>
environment variable contain the device URI), CUPS backends also expect specific environment variables and file descriptors, and typically run in a user session that (on macOS) has additional restrictions that affect how it runs.
Backends can also be installed with restricted permissions (0500 or 0700) that tell the scheduler to run them as the &quot;root&quot; user instead of an unprivileged user (typically &quot;lp&quot;) on the system.
</p>
    <p>Unless you are a developer and know what you are doing, please do not run backends directly.
Instead, use the
<a href="lp.html"><strong>lp</strong>(1)</a>

or
<a href="lpr.html"><strong>lpr</strong>(1)</a>

programs to send print jobs or
<a href="lpinfo.html"><strong>lpinfo</strong>(8)</a>

to query for available printers using the backend.
The one exception is the SNMP backend - see
<a href="cups-snmp.html"><strong>cups-snmp</strong>(8)</a>

for more information.
</p>
    <h2 id="backend-7.notes">Notes</h2>
<p>CUPS printer drivers and backends are deprecated and will no longer be supported in a future feature release of CUPS.
Printers that do not support IPP can be supported using applications such as
<a href="ippeveprinter.html"><strong>ippeveprinter</strong>(1).</a>

</p>
    <h2 id="backend-7.see-also">See Also</h2>
<p><em>cups</em>(1),

<em>cups-files.conf</em>(5),

<em>cups-snmp</em>(8),

<em>cupsd</em>(8),

<em>filter</em>(7),

<em>lp</em>(1),

<em>lpinfo</em>(8),

<em>lpr</em>(1),

<br>
CUPS Online Help (<a href="http://localhost:631/help">http://localhost:631/help</a>)
</p>
    <h2 id="backend-7.copyright">Copyright</h2>
<p>Copyright &copy; 2020-2024 by OpenPrinting.
  </body>
</html>
Commit	Line	Data
cc7359ae	1	<!DOCTYPE html>
94436c5a	2	<html>
cc7359ae	3	<head>
4e3aaa5e	4	<meta name="creator" content="mantohtml v2.0.2">
cc7359ae MS	5	<title>backend(7)</title>
	6	</head>
	7	<body>
	8	<h1 id="backend-7">backend(7)</h1>
	9	<h2 id="backend-7.name">Name</h2>
	10	<p>backend - cups backend transmission interfaces
	11	</p>
	12	<h2 id="backend-7.synopsis">Synopsis</h2>
	13	<p><strong>backend</strong>
c277f98c	14	<br>
cc7359ae MS	15	<strong>backend</strong>
	16	<em>job</em>
	17	<em>user</em>
	18	<em>title</em>
	19	<em>num-copies</em>
	20	<em>options</em>
bfbd0197	21	[
cc7359ae	22	<em>filename</em>
c277f98c	23	]
cc7359ae MS	24	</p>
	25	<pre>
	26	<strong>#include <cups/cups.h></strong>
bfbd0197	27
cc7359ae	28	<strong>const char cupsBackendDeviceURI</strong>(<strong>char *</strong><em>argv</em>);
bfbd0197	29
cc7359ae MS	30	<strong>void cupsBackendReport</strong>(<strong>const char *</strong><em>device_scheme</em>,
	31	<strong>const char *</strong><em>device_uri</em>,
	32	<strong>const char *</strong><em>device_make_and_model</em>,
	33	<strong>const char *</strong><em>device_info</em>,
	34	<strong>const char *</strong><em>device_id</em>,
	35	<strong>const char *</strong><em>device_location</em>);
bfbd0197	36
cc7359ae MS	37	<strong>ssize_t cupsBackChannelWrite</strong>(<strong>const char *</strong><em>buffer</em>,
cc7359ae MS	38	<strong>size_t </strong><em>bytes</em>, <strong>double </strong><em>timeout</em>);
94436c5a	39
cc7359ae MS	40	<strong>int cupsSideChannelRead</strong>(<strong>cups_sc_command_t *</strong><em>command</em>,
	41	<strong>cups_sc_status_t </strong><em>status</em>, <strong>char </strong><em>data</em>,
	42	<strong>int *</strong><em>datalen</em>, <strong>double </strong><em>timeout</em>);
bfbd0197	43
cc7359ae MS	44	<strong>int cupsSideChannelWrite</strong>(<strong>cups_sc_command_t </strong><em>command</em>,
	45	<strong>cups_sc_status_t </strong><em>status</em>, <strong>const char *</strong><em>data</em>,
	46	<strong>int </strong><em>datalen</em>, <strong>double </strong><em>timeout</em>);
bfbd0197	47	</pre>
cc7359ae MS	48	<h2 id="backend-7.description">Description</h2>
cc7359ae MS	49	<p>Backends are a special type of
4e3aaa5e	50	<a href="filter.html"><strong>filter</strong>(7)</a>
cc7359ae	51
bfbd0197	52	which is used to send print data to and discover different devices on the system.
cc7359ae MS	53	</p>
	54	<p>Like filters, backends must be capable of reading from a filename on the command-line or from the standard input, copying the standard input to a temporary file as required by the physical interface.
	55	</p>
	56	<p>The command name (<em>argv[0]</em>) is set to the device URI of the destination printer.
87030afb	57	Authentication information in
cc7359ae	58	<em>argv[0]</em>
bfbd0197	59	is removed, so backend developers are urged to use the
cc7359ae	60	<strong>DEVICE_URI</strong>
bfbd0197	61	environment variable whenever authentication information is required. The
cc7359ae MS	62	<strong>cupsBackendDeviceURI</strong>()
cc7359ae MS	63
bfbd0197	64	function may be used to retrieve the correct device URI.
cc7359ae MS	65	</p>
	66	<p>Back-channel data from the device should be relayed to the job filters using the <em>cupsBackChannelWrite</em> function.
	67	</p>
	68	<p>Backends are responsible for reading side-channel requests using the
	69	<strong>cupsSideChannelRead</strong>()
	70
bfbd0197	71	function and responding with the
cc7359ae MS	72	<strong>cupsSideChannelWrite</strong>()
cc7359ae MS	73
bfbd0197	74	function. The
cc7359ae	75	<strong>CUPS_SC_FD</strong>
bfbd0197	76	constant defines the file descriptor that should be monitored for incoming requests.
cc7359ae MS	77	</p>
	78	<h3 id="backend-7.description.device-discovery">Device Discovery</h3>
	79	<p>When run with no arguments, the backend should list the devices and schemes it supports or is advertising to the standard output.
87030afb	80	The output consists of zero or more lines consisting of any of the following forms:
cc7359ae MS	81	</p>
	82	<pre>
	83	device-class scheme "Unknown" "device-info"
	84	device-class device-uri "device-make-and-model" "device-info"
	85	device-class device-uri "device-make-and-model" "device-info" "device-id"
	86	device-class device-uri "device-make-and-model" "device-info" "device-id" "device-location"
94436c5a	87	</pre>
cc7359ae MS	88	<p>The
	89	<strong>cupsBackendReport</strong>()
	90
bfbd0197	91	function can be used to generate these lines and handle any necessary escaping of characters in the various strings.
cc7359ae MS	92	</p>
	93	<p>The
	94	<em>device-class</em>
bfbd0197	95	field is one of the following values:
cc7359ae MS	96	</p>
	97	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>direct</strong><br>
	98	The device-uri refers to a specific direct-access device with no options, such as a parallel, USB, or SCSI device.
	99	</p>
	100	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>file</strong><br>
	101	The device-uri refers to a file on disk.
	102	</p>
	103	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>network</strong><br>
	104	The device-uri refers to a networked device and conforms to the general form for
bfbd0197	105	network URIs.
cc7359ae MS	106	</p>
	107	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>serial</strong><br>
	108	The device-uri refers to a serial device with configurable baud rate and other options.
87030afb	109	If the device-uri contains a baud value, it represents the maximum baud rate supported by the device.
cc7359ae MS	110	</p>
	111	<p>The
	112	<em>scheme</em>
87030afb MS	113	field provides the URI scheme that is supported by the backend.
	114	Backends should use this form only when the backend supports any URI using that scheme.
	115	The
cc7359ae	116	<em>device-uri</em>
bfbd0197	117	field specifies the full URI to use when communicating with the device.
cc7359ae MS	118	</p>
	119	<p>The
	120	<em>device-make-and-model</em>
	121	field specifies the make and model of the device, e.g. "Example Foojet 2000".
	122	If the make and model is not known, you must report "Unknown".
	123	</p>
	124	<p>The
	125	<em>device-info</em>
87030afb	126	field specifies additional information about the device.
cc7359ae MS	127	Typically this includes the make and model along with the port number or network address, e.g. "Example Foojet 2000 USB #1".
	128	</p>
	129	<p>The optional
	130	<em>device-id</em>
bfbd0197	131	field specifies the IEEE-1284 device ID string for the device, which is used to select a matching driver.
cc7359ae MS	132	</p>
	133	<p>The optional
	134	<em>device-location</em>
bfbd0197	135	field specifies the physical location of the device, which is often used to pre-populate the printer-location attribute when adding a printer.
cc7359ae MS	136	</p>
	137	<h3 id="backend-7.description.permissions">Permissions</h3>
	138	<p>Backends without world read and execute permissions are run as the root user.
	139	Otherwise, the backend is run using an unprivileged user account, typically "lp".
	140	</p>
	141	<h2 id="backend-7.exit-status">Exit Status</h2>
	142	<p>The following exit codes are defined for backends:
	143	</p>
	144	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_OK</strong><br>
	145	The print file was successfully transmitted to the device or remote server.
	146	</p>
	147	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_FAILED</strong><br>
	148	<br>
87030afb MS	149	The print file was not successfully transmitted to the device or remote server.
87030afb MS	150	The scheduler will respond to this by canceling the job, retrying the job, or stopping the queue depending on the state of the
cc7359ae	151	<em>printer-error-policy</em>
94436c5a	152	attribute.
cc7359ae MS	153	</p>
	154	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_AUTH_REQUIRED</strong><br>
	155	The print file was not successfully transmitted because valid authentication information is required.
	156	The scheduler will respond to this by holding the job and adding the 'cups-held-for-authentication' keyword to the "job-reasons" Job Description attribute.
	157	</p>
	158	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_HOLD</strong><br>
	159	The print file was not successfully transmitted because it cannot be printed at this time.
87030afb	160	The scheduler will respond to this by holding the job.
cc7359ae MS	161	</p>
	162	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_STOP</strong><br>
	163	The print file was not successfully transmitted because it cannot be printed at this time.
87030afb	164	The scheduler will respond to this by stopping the queue.
cc7359ae MS	165	</p>
	166	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_CANCEL</strong><br>
	167	The print file was not successfully transmitted because one or more attributes are not supported or the job was canceled at the printer.
87030afb	168	The scheduler will respond to this by canceling the job.
cc7359ae MS	169	</p>
	170	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_RETRY</strong><br>
	171	The print file was not successfully transmitted because of a temporary issue.
87030afb	172	The scheduler will retry the job at a future time - other jobs may print before this one.
cc7359ae MS	173	</p>
	174	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>CUPS_BACKEND_RETRY_CURRENT</strong><br>
	175	The print file was not successfully transmitted because of a temporary issue.
87030afb	176	The scheduler will retry the job immediately without allowing intervening jobs.
cc7359ae MS	177	</p>
	178	<p>All other exit code values are reserved.
	179	</p>
	180	<h2 id="backend-7.environment">Environment</h2>
	181	<p>In addition to the environment variables listed in
4e3aaa5e	182	<a href="cups.html"><strong>cups</strong>(1)</a>
cc7359ae	183
bfbd0197	184	and
4e3aaa5e	185	<a href="filter.html"><strong>filter</strong>(7),</a>
cc7359ae	186
bfbd0197	187	CUPS backends can expect the following environment variable:
cc7359ae MS	188	</p>
	189	<p style="margin-left: 2.5em; text-indent: -2.5em;"><strong>DEVICE_URI</strong><br>
	190	The device URI associated with the printer.
	191	</p>
	192	<h2 id="backend-7.files">Files</h2>
	193	<p><em>/etc/cups/cups-files.conf</em>
	194	</p>
	195	<h2 id="backend-7.notes">Notes</h2>
	196	<p>CUPS backends are not generally designed to be run directly by the user.
87030afb	197	Aside from the device URI issue (
cc7359ae	198	<em>argv[0]</em>
bfbd0197	199	and
cc7359ae	200	<strong>DEVICE_URI</strong>
87030afb	201	environment variable contain the device URI), CUPS backends also expect specific environment variables and file descriptors, and typically run in a user session that (on macOS) has additional restrictions that affect how it runs.
cc7359ae MS	202	Backends can also be installed with restricted permissions (0500 or 0700) that tell the scheduler to run them as the "root" user instead of an unprivileged user (typically "lp") on the system.
	203	</p>
	204	<p>Unless you are a developer and know what you are doing, please do not run backends directly.
87030afb	205	Instead, use the
4e3aaa5e	206	<a href="lp.html"><strong>lp</strong>(1)</a>
cc7359ae	207
bfbd0197	208	or
4e3aaa5e	209	<a href="lpr.html"><strong>lpr</strong>(1)</a>
cc7359ae	210
bfbd0197	211	programs to send print jobs or
4e3aaa5e	212	<a href="lpinfo.html"><strong>lpinfo</strong>(8)</a>
cc7359ae	213
87030afb MS	214	to query for available printers using the backend.
87030afb MS	215	The one exception is the SNMP backend - see
4e3aaa5e	216	<a href="cups-snmp.html"><strong>cups-snmp</strong>(8)</a>
cc7359ae	217
bfbd0197	218	for more information.
cc7359ae MS	219	</p>
	220	<h2 id="backend-7.notes">Notes</h2>
	221	<p>CUPS printer drivers and backends are deprecated and will no longer be supported in a future feature release of CUPS.
87030afb	222	Printers that do not support IPP can be supported using applications such as
4e3aaa5e	223	<a href="ippeveprinter.html"><strong>ippeveprinter</strong>(1).</a>
cc7359ae MS	224
	225	</p>
	226	<h2 id="backend-7.see-also">See Also</h2>
	227	<p><em>cups</em>(1),
	228
	229	<em>cups-files.conf</em>(5),
	230
	231	<em>cups-snmp</em>(8),
	232
	233	<em>cupsd</em>(8),
	234
	235	<em>filter</em>(7),
	236
	237	<em>lp</em>(1),
	238
	239	<em>lpinfo</em>(8),
	240
	241	<em>lpr</em>(1),
	242
bfbd0197 MS	243	<br>
bfbd0197 MS	244	CUPS Online Help (<a href="http://localhost:631/help">http://localhost:631/help</a>)
cc7359ae MS	245	</p>
cc7359ae MS	246	<h2 id="backend-7.copyright">Copyright</h2>
76b6aade	247	<p>Copyright © 2020-2024 by OpenPrinting.
cc7359ae	248	</body>
94436c5a	249	</html>