sane-usb - USB configuration tips for SANE
This manual page contains information on how to access scanners with a USB interface.
This manual page describes the access of USB scanners over the sanei_usb interface. Most
SANE USB backends use the sanei_usb interface, only sm3600 accesses the USB directly by
libusb. Have a look at sane-sm3600 and section "LIBUSB ACCESS TIPS" of this manual page
for that backend.
Two methods for accessing USB devices are used by sanei_usb: direct access using the ker-
nel scanner driver and access over libusb. sanei_usb tries both methods, if they are
available. Currently USB access is tested for Linux (kernel, libusb), FreeBSD (kernel,
libsub), NetBSD (libusb), and OpenBSD (kernel, libusb). Libusb access should also work on
Mac OS X (Darwin) and any other operating system supported by libusb but hasn't been
tested yet. For installation issues, also check the /usr/share/doc/sane-back-
Most backends will detect USB scanners automatically using "usb" configuration file lines.
This method allows to identify scanners by the USB vendor and product numbers. The syntax
for specifying a scanner this way is:
usb VENDOR PRODUCT
where VENDOR is the USB vendor id, and PRODUCT is the USB product id of the scanner. Both
ids are non-negative integer numbers in decimal or hexadecimal format. The correct values
for these fields can be found by looking into the syslog (e.g., /var/log/messages) or
under Linux by issuing the command "cat /proc/bus/usb/devices/". This is an example of a
config file line:
usb 0x055f 0x0006
would have the effect that all USB devices in the system with a vendor id of 0x55f and a
product id of 0x0006 would be probed and recognized by the backend. The same config line
in decimal format looks like this:
usb 1375 6
If your scanner is not detected automatically, it may be necessary to edit the appropriate
backend configuration file before using SANE for the first time. For most systems, the
configuration file should list the name of the USB device file that the scanner is con-
nected to (e.g., under Linux, /dev/usb/scanner0 or /dev/usbscanner0 is such a USB device,
the device file for FreeBSD is e.g. /dev/uscanner0). If libusb is used, the device name
looks like the following example: libusb:001:002
Do not create a symlink from /dev/scanner to the USB device because this link is used by
the SCSI backends. The scanner may be confused if it receives SCSI commands.
For a detailed description of each backend's configuration file, please refer to the rele-
vant backend manual page (e.g. sane-mustek_usb for Mustek USB scanners).
WHEN TO USE WHICH ACCESS METHOD
Generally speaking, if your scanner works with one method, there is no need to switch to
the other one.
Libusb is the more general approach and will be able to access any scanner. Also, it sup-
ports more platforms. However, the library must be available and installed on the system
and setting permissions isn't easy at least on Linux.
Autodetecting scanners and using USB control messages with the kernel access method only
works with recent (>=v2.4.12) Linux kernels. If you need one of these two features on a
different platform, use libusb instead.
KERNEL SCANNER DRIVER TIPS
Ensure that the access permissions for the USB device are set appropriately. We recommend
to add a group "scanner" to /etc/group which contains all users that should have access to
the scanner. The permission of the device should then be set to allow group read and
write access. For example, if the scanner is at USB device /dev/usb/scanner0, then the
following two commands would set the permission correctly:
$ chgrp scanner /dev/usb/scanner0
$ chmod 660 /dev/usb/scanner0
If your scanner isn't detected automatically by your operating system's scanner driver,
you need to tell the kernel the vendor and product ids of your scanner. For Linux, this
can be done with modprobe parameters: First, remove the scanner module (rmmod scanner),
then load it again: modprobe scanner vendor=0x0001 product=0x0002. Use the appropriate
vendor and product ids (e.g. from syslog or cat /proc/bus/usb/devices). For OpenBSD the
kernel must be recompiled. For details look at /usr/share/doc/sane-back-
ends-1.0.9/README.openbsd. Similar approaches should be used for the other BSDs.
Linux kernel messages in syslog like "kernel: scanner.c: open_scanner(1): Unable to access
minor data" can be ignored. They are generated when SANE scans all available USB devices
LIBUSB ACCESS TIPS
Libusb can only access your scanner if it's not claimed by the kernel scanner driver. If
you want to use libusb, unload the kernel driver (e.g. rmmod scanner under Linux) or dis-
able the driver when compiling a new kernel. For Linux, your kernel needs support for the
USB filesystem (usbfs) and that filesystem must be mounted. That's done automatically, if
/etc/fstab contains a line like this:
none /proc/bus/usb usbfs defaults 0 0
The permissions for the device files used by libusb must be adjusted for user access. Oth-
erwise only root can use SANE devices. For Linux, the devices are located in
/proc/bus/usb/. There are directories named e.g. "001" (the bus name) containing files
"001", "002" etc. (the device files). The right device files can be found out by running
scanimage -L as root. Setting permissions with "chmod" is not permanent, however. They
will be resetted after reboot or replugging the scanner. It's also possible to mount the
usbfs with the option "devmode=0666", e.g. by using the following line in /etc/fstab:
none /proc/bus/usb usbfs defaults,devmode=0666 0 0
However, this way everyone has access to all USB devices. Another way to set permissions
is to use the hotplug utilities (http://linux-hotplug.sourceforge.net/), which support
dynamic setting of access permissions. Last, the frontends can be run as root. However,
that's not recommended for security reasons.
For the BSDs, the device files are named /dev/ugen*. Use chmod to apply appropriate per-
If the library was compiled with debug support enabled, this environment variable
controls the debug level for the USB I/O subsystem. E.g., a value of 128 requests
all debug output to be printed. Smaller levels reduce verbosity. Values greater
than 4 enable libusb debugging (if available).
sane(7), sane-find-scanner(1), sane-"backendname"(5), sane-scsi(5)
Henning Meier-Geinitz. Some parts were copied from the sane-scsi manual page.
15 Sep 2002 sane-scsi(5)