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Revision 31 as of 2018-02-22 12:43:59
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Comment: Corrected advice to test the serever as an ordinary user.
Revision 32 as of 2018-03-01 18:41:54
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Editor: Brian Potkin
Comment: Transferred "Scanning over WiFi with AirPrint / eSCL Scanners" from the Scanner wiki page to here. It is a more appropriate place for it.
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Sharing a USB or network scanner over a network with SANE.
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'''Sharing a USB or network scanner over a network with SANE.'''
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[[#server|sharing a network HP aio scanner]] is not possible due to bugs DebianBug:807427 and DebianBug:838212. Network scanners from other vendors might work in sharing mode though. [[#server|sharing a network HP aio scanner]] is not possible due to bugs DebianBug:807427 and DebianBug:838212. Network scanners from other vendors might work in sharing mode though.

<<Anchor(airprint)>>
= Scanning over WiFi with AirPrint / eSCL Scanners =

Except for the [[#aio3|aforementioned HP scanners]], most AirPrint / eSCL scanners are currently (as of 2017) not supported by Sane. But since the protocol is a simple XML and HTTP based protocol, the rudimentary (command line) python script https://github.com/kno10/python-scan-eSCL can be used to scan with such devices. As this may be the preferred way to support Mac OS X, it may become increasingly common.

Example devices that work with this include: Canon PIXMA TS5050 (and probably other Canon PIXMA TS models), and [[https://lists.alioth.debian.org/pipermail/sane-devel/2017-August/035588.html|according to sane-devel]] it can be modified to also support Kyocera and HP. But of course it would be best if someone added a eSCL/AirPrint driver to SANE, so you can use all GUIs.

Translation(s): English - Français - Italiano


Sharing a USB or network scanner over a network with SANE.

Introduction

       SCANNER                         SERVER                                       CLIENT
 +-------------------+       +------------------------+                +-----------------------------+
 |   Non-networked   |       | libsane + sane-utils   |                | libsane                     |
 |   stand-alone or  |  USB  |                        | cable/wireless |                             |
 |   multifunctional |<----->| saned.conf: permitted  |<-------------->| dll.conf: uncomment net     |
 |       device      |       |            connections |                | net.conf: server IP address |
 +-------------------+       +------------------------+                +-----------------------------+

This page is written principally in the context of a user with Debian 8 (jessie) or Debian 9 (stretch) installed. Both distributions have an init system (the first process started during booting of the computer and which governs its subsequent behaviour) based on systemd. On a machine with a scanner connected to a USB port (the server), SANE with systemd can be socket activated (check that the service is enabled). The saned daemon is started when a request is received on the server from a client and is stopped when the request is fulfilled. This forms the basis for a scanner shared by the server to serve up an image of a document to an application on a client.

Essentially, saned on the server and the net backend on the client are used to convert a non-networked or network-incapable scanner into a networked one.

      SCANNER                                 CLIENT
+-----------------+                +--------------------------+
| Network-capable |                |                          |
| stand-alone or  | cable/wireless | libsane                  |
| multifunctional |<-------------->| Vendor-specific packages |
|     device      |                |                          |       
+-----------------+                +--------------------------+

A scanner which is network enabled with a cabled or wireless connection (a network scanner) is accessed with the help of libsane and one of its collection of backends. Consult a backend's manual for information on whether the backend supports scanning over the network. For example, theepson2 and pixma backends do. libsane interworks with the non-SANE, HP-provided hpaio backend. Other vendors also provide a means to access a network-capable scanner but there is generally a non-free aspect to what they offer, so configuration of their devices is not treated on this page.

Sharing a USB Connected Scanner

Server Configuration

  • Install sane-utils to get saned.

  • Check that the contents of /etc/default/saned fit the system and that saned is in the scanner group. No changes need be made to this file for the vast majority of users. You should see this:

$ groups saned
saned : saned scanner
  • Add the hostnames, IP addresses or IP subnets that are permitted to use local SANE devices on the server in /etc/sane.d/saned.conf. For example, you could allow the local network using the following configuration, which will vary according to your network configuration:

192.168.0.1/24
  • If necessary (look at systemctl status saned.socket) and enable the systemd socket service:

$ sudo systemctl enable saned.socket
Created symlink from /etc/systemd/system/sockets.target.wants/saned.socket to /lib/systemd/system/saned.socket.
$ sudo systemctl start saned.socket
$ sudo systemctl status saned.socket
  • The server will now be sharing the USB connected scanner with other designated machines on the network.

A first installation of libsane has the socket service disabled, so it would be necessary to enable and start it as described above.

Client Configuration

  • It is essential to install libsane and, for testing the client's ability to see the networked scanner, it is recommended to install sane-utils. Success in detecting the shared scanner with scanimage indicates probable success with other frontends.

  • Uncomment the net backend entry in /etc/sane.d/dll.conf.

  • Add the IP address/hostname of the sane server to /etc/sane.d/net.conf.

  • If everything is working correctly you should get something like this:

% scanimage -L
device `net:192.168.0.100:plustek:libusb:002:006' is a Canon N670U/N676U/LiDE20 USB flatbed scanner

Note that the net backend is not for accessing arbitrary scanners over a network. It's intended use is for the server (which has a SANE-supported scanner) to be able to export that scanner to clients on the network via a single SANE-specific, manufacturer-agnostic protocol.

Troubleshooting

Make sure the saned user can access the scanner locally on the server. scanimage -L should detect the scanner if there is a backend on the system for it and the saned user has permission to access the USB bus; sane-find-scanner will indicate whether the saned user does have permission.

To run as the saned user either become root with su and do

su -s /bin/bash saned
sane-find-scanner
scanimage -L

or use sudo:

sudo-u saned sane-find-scanner
sudo-u saned scanimage -L

Also see how a USB scanner is set up for more information on the local configuration.

Having an ordinary user with or without permissions on the USB bus (libpam-systemd might not be installed) is of no consequence. It is the saned user which needs the permissions.

Bear in mind that sane-find-scanner does a generic USB scan; success indicates a user has sufficient privileges to access the USB devices. On the other hand, a negative response to scanimage -L means that none of the SANE or vendor-supplied backends have knowledge of this model of scanner, so will not talk to it.

If the scanner works on the server but not remotely, make sure the saned.socket service is running correctly on the server; systemctl should tell you this:

$ systemctl status saned.socket
● saned.socket - saned incoming socket
   Loaded: loaded (/lib/systemd/system/saned.socket; enabled)
   Active: active (listening) since Wed 2017-11-15 22:28:05 UTC; 1s ago
   Listen: [::]:6566 (Stream)
 Accepted: 0; Connected: 0

Nov 15 22:28:05 mafalda systemd[1]: Listening on saned incoming socket.

You should also be able to ping the host configured:

$ ping -c1 mafalda
PING mafalda.anarc.at (192.168.0.6) 56(84) bytes of data.
64 bytes from mafalda.anarc.at (192.168.0.6): icmp_seq=1 ttl=64 time=0.400 ms

--- mafalda.anarc.at ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.400/0.400/0.400/0.000 ms

You can also try to connect directly to the scanner with:

xsane net:192.168.0.6

If you have trouble connecting multiple computers to the server, systemctl status saned.socket might show:

saned.socket: Too many incoming connections (1), dropping connection.

This is a known bug in the systemd unit. For a workaround on jessie or stretch:

  • cp /lib/systemd/system/saned.socket /etc/systemd/system/saned.socket.

  • Edit and replace MaxConnections=1 with MaxConnections=64.

  • systemctl daemon-reload.

On stretch it is probably more convenient to do:

  • systemctl edit --full saned.socket.

Network Scanner Configurations

Scanning with a Network HP all-in-one (aio)-1

To scan over the network from a scanner on an HP aio (one which is not connected by USB to a computer) you need only to install libsane-hpaio (without its recommended packages) and pass the URI of the scanner to the frontend. A non-free plugin might be required for the scanning function.

The format of the URI is:

hpaio:/net/<aio_model_name>?ip=<IP_address_of_the_aio>

This URI can be given directly to the frontend. It can also be provided automatically to the frontend if either a print queue with the hp:/... backend is set up or mDNS broadcasts for the scanner are done by the aio. Automatic discovery will happen via the print queue if both it and mDNS are available as discovery methods.

The IP address could be known from the way the aio's networking was set up; or it could be got from the aio's front panel or deduced from the output of

/usr/bin/lpinfo -v

Each printer model supported by the installed verion of libsane-hpaio is listed in /usr/share/hplip/data/models/models.dat. Model names are enclosed in square brackets; like so, [envy_4500_series].

A frontend can be started with (for example):

simple-scan <URI>

Typing the URI each time can be avoided by exploring what your DE (Desktop Environment) or WM (Window Manager) offers for customising a command. For typing from a terminal you might find a simple alias sufficient.

An hplip installation pulls in libsane-hpaio as a dependency and hplip provides the utility hp-makeuri. It can be used instead of the previous technique for finding a URI. A needed plugin can also be installed with hp-plugin.

Scanning with a Network HP all-in-one (aio)-2

Many users will configure an HP aio machine by installing hplip or hplip-gui and setting up the printing side of the device with hp-setup. Scanning should now be automatically available, as explained by a user on sane-devel and by an hplipopensource troubleshooting page. Simply typing the name of a favourite frontend or clicking on a menu entry should be sufficient to run the application:

simple-scan
xsane
xscanimage

The URI to pass to the frontend is obtained from the printer URI by replacing hp:/... with hpaio:/....

Setting up a printer with other device URIs, socket://..., ipp://... etc, will not give this automatic discovery of a scanner URI.

Scanning with a Network HP all-in-one (aio)-3

      SCANNER                            ClIENT 
+------------------+                +---------------+
| Stand-alone or   |                | libsane       |
| multifunctional  | cable/wireless |               |
| AirPrint-enabled |<-------------->| libsane-hpaio |
|     device       | mDNS packets-->|    package    |
+---------------- -+                +---------------+

Recent HP aios (since 2010) will probably come with AirPrint. When activated on the aio the URI of the scanner is formed from the mDNS broadcasts of the aio in co-operation with /usr/share/hplip/data/models/models.dat. Without setting up the printing function of the aio the scanner should be detected by

scanimage -L

and the frontend should automatically run after doing

xsane
simple-scan
xscanimage

sharing a network HP aio scanner is not possible due to bugs 807427 and 838212. Network scanners from other vendors might work in sharing mode though.

Scanning over WiFi with AirPrint / eSCL Scanners

Except for the aforementioned HP scanners, most AirPrint / eSCL scanners are currently (as of 2017) not supported by Sane. But since the protocol is a simple XML and HTTP based protocol, the rudimentary (command line) python script https://github.com/kno10/python-scan-eSCL can be used to scan with such devices. As this may be the preferred way to support Mac OS X, it may become increasingly common.

Example devices that work with this include: Canon PIXMA TS5050 (and probably other Canon PIXMA TS models), and according to sane-devel it can be modified to also support Kyocera and HP. But of course it would be best if someone added a eSCL/AirPrint driver to SANE, so you can use all GUIs.

Inetd Configuration

An alternative to systemd socket activation is to use openbsd-inetd. Install it, take a look at /etc/default/saned and run

update-inetd --enable sane-port

See Also