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NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | ENVIRONMENT | FILES | NOTES | NOTES | SEE ALSO | COPYRIGHT | COLOPHON |
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backend(7) Apple Inc. backend(7)
backend - cups backend transmission interfaces
backend
backend job user title num-copies options [ filename ]
#include <cups/cups.h>
const char *cupsBackendDeviceURI(char **argv);
void cupsBackendReport(const char *device_scheme,
const char *device_uri,
const char *device_make_and_model,
const char *device_info,
const char *device_id,
const char *device_location);
ssize_t cupsBackChannelWrite(const char *buffer,
size_t bytes, double timeout);
int cupsSideChannelRead(cups_sc_command_t *command,
cups_sc_status_t *status, char *data,
int *datalen, double timeout);
int cupsSideChannelWrite(cups_sc_command_t command,
cups_sc_status_t status, const char *data,
int datalen, double timeout);
Backends are a special type of filter(7) which is used to send
print data to and discover different devices on the system.
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.
The command name (argv[0]) is set to the device URI of the
destination printer. Authentication information in argv[0] is
removed, so backend developers are urged to use the DEVICE_URI
environment variable whenever authentication information is
required. The cupsBackendDeviceURI() function may be used to
retrieve the correct device URI.
Back-channel data from the device should be relayed to the job
filters using the cupsBackChannelWrite function.
Backends are responsible for reading side-channel requests using
the cupsSideChannelRead() function and responding with the
cupsSideChannelWrite() function. The CUPS_SC_FD constant defines
the file descriptor that should be monitored for incoming
requests.
DEVICE DISCOVERY
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:
device-class scheme "Unknown" "device-info"
device-class device-uri "device-make-and-model" "device-info"
device-class device-uri "device-make-and-model" "device-info" "device-id"
device-class device-uri "device-make-and-model" "device-info" "device-id" "device-location"
The cupsBackendReport() function can be used to generate these
lines and handle any necessary escaping of characters in the
various strings.
The device-class field is one of the following values:
direct
The device-uri refers to a specific direct-access device
with no options, such as a parallel, USB, or SCSI device.
file The device-uri refers to a file on disk.
network
The device-uri refers to a networked device and conforms to
the general form for network URIs.
serial
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.
The scheme 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 device-uri field
specifies the full URI to use when communicating with the device.
The device-make-and-model field specifies the make and model of
the device, e.g. "Example Foojet 2000". If the make and model is
not known, you must report "Unknown".
The device-info field specifies additional information about the
device. Typically this includes the make and model along with
the port number or network address, e.g. "Example Foojet 2000 USB
#1".
The optional device-id field specifies the IEEE-1284 device ID
string for the device, which is used to select a matching driver.
The optional device-location field specifies the physical
location of the device, which is often used to pre-populate the
printer-location attribute when adding a printer.
PERMISSIONS
Backends without world read and execute permissions are run as
the root user. Otherwise, the backend is run using an
unprivileged user account, typically "lp".
The following exit codes are defined for backends:
CUPS_BACKEND_OK
The print file was successfully transmitted to the device or
remote server.
CUPS_BACKEND_FAILED
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 printer-error-policy
attribute.
CUPS_BACKEND_AUTH_REQUIRED
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 "job-reasons"
Job Description attribute.
CUPS_BACKEND_HOLD
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.
CUPS_BACKEND_STOP
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.
CUPS_BACKEND_CANCEL
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.
CUPS_BACKEND_RETRY
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.
CUPS_BACKEND_RETRY_CURRENT
The print file was not successfully transmitted because of a
temporary issue. The scheduler will retry the job
immediately without allowing intervening jobs.
All other exit code values are reserved.
In addition to the environment variables listed in cups(1) and
filter(7), CUPS backends can expect the following environment
variable:
DEVICE_URI
The device URI associated with the printer.
/etc/cups/cups-files.conf
CUPS backends are not generally designed to be run directly by
the user. Aside from the device URI issue ( argv[0] and
DEVICE_URI 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 "root" user instead of
an unprivileged user (typically "lp") on the system.
Unless you are a developer and know what you are doing, please do
not run backends directly. Instead, use the lp(1) or lpr(1)
programs to send print jobs or lpinfo(8) to query for available
printers using the backend. The one exception is the SNMP
backend - see cups-snmp(8) for more information.
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 ippeveprinter(1).
cups(1), cups-files.conf(5), cups-snmp(8), cupsd(8), filter(7),
lp(1), lpinfo(8), lpr(1),
CUPS Online Help (http://localhost:631/help)
Copyright © 2007-2019 by Apple Inc.
This page is part of the CUPS (a standards-based, open source
printing system) project. Information about the project can be
found at ⟨http://www.cups.org/⟩. If you have a bug report for
this manual page, see ⟨http://www.cups.org/⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/apple/cups⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2023-10-27.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
26 April 2019 CUPS backend(7)
Pages that refer to this page: filter(7), cupsd(8), cupsd-helper(8), cups-snmp(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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