The problem of scanning using USB multi-function printers in Linux (success at last)

After my investigations described in a couple of earlier posts ([1], [2]), I finally got Gentoo Linux to scan reliably via the USB connection to my Canon MP560 MFP (multi-function peripheral), a single USB device with three interfaces: scanner (Interface 0); printer (Interface 1); mass storage (Interface 2). Well, ninety-nine per cent reliably, if that isn’t a contradiction in terms. The formula for success? I had to do all the following:

  1. Stop the kernel from binding the usb-storage driver to the device.

  2. Create a UDEV rule to modify the ACL (access control list) of the device to give both the ‘lp‘ and ‘scanner‘ groups Read-Write access to the device.

  3. Create a UDEV rule to: a) change the owner of the device from ‘root‘ to my user account (fitzcarraldo); b) change the device’s group to ‘scanner‘ instead of ‘lp‘; c) give all users Read-Write access to the device (see my note about this at the end of this post).

  4. Disable the SANE backend from accessing the MP560 via the network.

Let’s look in more detail at each of these …

Stop the kernel from binding the usb-storage driver to the device

Originally I had built the usb-storage driver into the kernel (CONFIG_USB_STORAGE=y). During the course of my investigations into this problem I rebuilt the kernel with CONFIG_USB_STORAGE=m, i.e. I rebuilt the driver as an external module, although it should not matter either way.

The vendor ID (04a9) and product ID (173e) of the MP560 can be found using the lsusb command:

# lsusb | grep -i canon
Bus 001 Device 007: ID 04a9:173e Canon, Inc. MP560

If the usb-storage driver is built as an external module, the kernel configuration file will include the following:

# grep CONFIG_USB_STORAGE= /usr/src/linux/.config
CONFIG_USB_STORAGE=m

In this case, it is possible to stop the driver binding to the USB storage interface in the MP560 by creating a ‘quirk’ in the file /etc/modprobe.d/usb-storage.conf as shown below:

# cat /etc/modprobe.d/usb-storage.conf
options usb-storage quirks=04a9:173e:i

If the usb-storage driver is built into the kernel, the kernel configuration file will include the following:

# grep CONFIG_USB_STORAGE= /usr/src/linux/.config
CONFIG_USB_STORAGE=y

In this case, it is possible to stop the driver binding to the USB storage interface in the MP560 by adding a ‘quirk’ (usb-storage.quirks=<idVendor>:<idProduct>:i) to the kernel boot line as shown below (ignore the rest of the parameters shown below, as yours are likely to be different):

# grep usb-storage /boot/grub/grub.cfg
linux /vmlinuz-3.18.11-gentoo root=/dev/sda5 ro drm_kms_helper.edid_firmware=edid/1920x1080_Clevo_W230SS.bin i915.modeset=1 rcutree.rcu_idle_gp_delay=1 usb-storage.quirks=04a9:173e:i

If you edit the file /boot/grub/grub.cfg directly, the change will be lost if you rebuild or upgrade in future. The ‘proper’ way to add the quirk would be to add it to the list of kernel boot parameters in GRUB_CMDLINE_LINUX_DEFAULT in the file /etc/default/grub and regenerate grub.cfg using the command ‘grub2-mkconfig -o /boot/grub/grub.cfg‘.

Create a UDEV rules file to modify the device’s ACL

I created a UDEV rules file /etc/udev/rules.d/99-canon-mp560.rules containing the following:

# ACL settings for Canon PIXMA MP560 printer MFP
ATTR{idVendor}=="04a9", ATTR{idProduct}=="173e", GOTO="canon"
GOTO="canon_end"
 
LABEL="canon"
RUN+="/bin/setfacl -m g:scanner:rw -m g:lp:rw $env{DEVNAME}"
TEST=="/var/run/ConsoleKit/database", \
        RUN+="udev-acl --action=$env{ACTION} --device=$env{DEVNAME}"
 
LABEL="canon_end"

Create a UDEV rules file to change the owner, group and permissions of the device

The file 41-libsane.rules in my installation is the only UDEV rules file in the directory /lib/udev/rules.d/ that explicitly mentions the MP560:

# grep 173e /lib/udev/rules.d/*
/lib/udev/rules.d/41-libsane.rules:ATTRS{idVendor}=="04a9", ATTRS{idProduct}=="173e", MODE="0664", GROUP="scanner", ENV{libsane_matched}="yes"

As the USB device was always in the ‘lp‘ group (see the output of the ‘ls -la‘ command [1]), the above UDEV rule was clearly being overridden by another rule, but which one in the long list of rules files created automatically when I installed the OS and various packages (see below)?

# ls -F1 /lib/udev/rules.d/
10-ft-rockey.rules
10-virtualbox.rules
40-gentoo.rules
40-usb-media-players.rules
41-libsane.rules
42-usb-hid-pm.rules
50-udev-default.rules
56-hpmud.rules
60-block.rules
60-cdrom_id.rules
60-drm.rules
60-evdev.rules
60-persistent-alsa.rules
60-persistent-input.rules
60-persistent-storage-tape.rules
60-persistent-storage.rules
60-persistent-v4l.rules
60-serial.rules
61-accelerometer.rules
64-btrfs.rules
69-cd-sensors.rules
70-libgphoto2.rules
70-mouse.rules
70-printers.rules
70-touchpad.rules
70-udev-acl.rules
75-net-description.rules
75-probe_mtd.rules
77-mm-cinterion-port-types.rules
77-mm-ericsson-mbm.rules
77-mm-huawei-net-port-types.rules
77-mm-longcheer-port-types.rules
77-mm-mtk-port-types.rules
77-mm-nokia-port-types.rules
77-mm-pcmcia-device-blacklist.rules
77-mm-platform-serial-whitelist.rules
77-mm-simtech-port-types.rules
77-mm-telit-port-types.rules
77-mm-usb-device-blacklist.rules
77-mm-usb-serial-adapters-greylist.rules
77-mm-x22x-port-types.rules
77-mm-zte-port-types.rules
77-nm-olpc-mesh.rules
78-sound-card.rules
80-drivers.rules
80-mm-candidate.rules
80-net-name-slot.rules
80-udisks2.rules
85-regulatory.rules
90-alsa-restore.rules
90-libgpod.rules
90-network.rules
90-pulseaudio.rules
95-cd-devices.rules
95-upower-battery-recall-dell.rules
95-upower-battery-recall-fujitsu.rules
95-upower-battery-recall-gateway.rules
95-upower-battery-recall-ibm.rules
95-upower-battery-recall-lenovo.rules
95-upower-battery-recall-toshiba.rules
95-upower-csr.rules
95-upower-hid.rules
95-upower-wup.rules
97-hid2hci.rules
99-fuse.rules
99-ntfs3g.rules
99-nvidia.rules

Anyway, I created a UDEV rules file /etc/udev/rules.d/95-libsane.rules to change the owner of the MP560 USB device from ‘root‘ to me (i.e. user name ‘fitzcarraldo‘), to put the device in the ‘scanner‘ group instead of the ‘lp‘ group, and to give all users Read-Write permission for the device:

ATTRS{idVendor}=="04a9", ATTRS{idProduct}=="173e", MODE="0666", OWNER="fitzcarraldo", GROUP="scanner", ENV{libsane_matched}="yes"

So I now have two user-created UDEV rules files:

# ls /etc/udev/rules.d/
95-libsane.rules 99-canon-mp560.rules

Note that user-created UDEV rules files should be put in the directory /etc/udev/rules.d/, not the directory /lib/udev/rules.d/ which is reserved for UDEV rules installed when you install the OS and by packages you install later. Unfortunately, there is no consistency in UDEV rules file names and their contents between Linux distributions, which makes debugging UDEV rules even more difficult. Higher numbered rules files override lower-numbered rules files.

I then switched off the MP560 and switched it on again. The two UDEV rules files I created had worked as intended. The ownership and group of the device had changed, and so had the permissions and ACL:

# ls -la /dev/bus/usb/001
total 0
drwxr-xr-x  2 root         root       200 Jul 29 10:10 .
drwxr-xr-x  4 root         root        80 Jul 29 09:56 ..
crw-rw-r--  1 root         usb     189, 0 Jul 29 11:25 001
crw-rw-r--  1 root         usb     189, 1 Jul 29 09:56 002
crw-rw-r--  1 root         usb     189, 2 Jul 29 11:25 003
crw-rw-r--  1 root         usb     189, 3 Jul 29 09:56 004
crw-rw-r--  1 root         usb     189, 4 Jul 29 11:25 005
crw-rw-r--  1 root         usb     189, 5 Jul 29 11:25 006
crw-rw-r--  1 root         usb     189, 7 Jul 29 11:25 008
crw-rw-rw-+ 1 fitzcarraldo scanner 189, 8 Jul 29 11:27 009

# getfacl /dev/bus/usb/001/009
getfacl: Removing leading '/' from absolute path names
# file: dev/bus/usb/001/009
# owner: fitzcarraldo
# group: scanner
user::rw-
user:fitzcarraldo:rw-
group::rw-
group:lp:rw-
group:scanner:rw-
mask::rw-
other::rw-

Disable the SANE backend from accessing the MP560 via the network

Although scanning via the USB connection sometimes still works if I have also specified a network connection in the file /etc/sane.d/pixma.conf, apparently the two interfaces should not normally be enabled simultaneously. See the post [sane-devel] Pixma 530 series – tested and not working by SANE developer Rolf Bensch:

Please disconnect the scanner from network and try again. The backend
has problems if both network and USB are connected at once.

Therefore, to try using SANE to access the MP560 via USB, I disabled network access to the MP560 by commenting out the URI in the relevant SANE backend configuration file, which in the case of the MP560 is the file /etc/sane.d/pixma.conf. I commented out the line ‘bjnp://192.168.1.78‘ which I had previously inserted to enable me to scan via my home network because the USB connection was unreliable.

Trying to scan

I then checked if the USB-connected scanner is detected by SANE when running as root user and when running under my user account:

# scanimage -L
device `pixma:04A9173E_1653C4' is a CANON Canon PIXMA MP560 multi-function peripheral
# sane-find-scanner -q
found USB scanner (vendor=0x04a9 [Canon], product=0x173e [MP560 series]) at libusb:001:010
# exit
exit
$ scanimage -L
device `pixma:04A9173E_1653C4' is a CANON Canon PIXMA MP560 multi-function peripheral
$ sane-find-scanner -q
found USB scanner (vendor=0x04a9 [Canon], product=0x173e [MP560 series]) at libusb:001:010

The test using the scanimage command worked:

$ scanimage -d pixma:04A9173E_1653C4 -T
scanimage: scanning image of size 638x877 pixels at 24 bits/pixel
scanimage: acquiring RGB frame, 8 bits/sample
scanimage: reading one scanline, 1914 bytes...  PASS
scanimage: reading one byte...          PASS
scanimage: stepped read, 2 bytes...     PASS
scanimage: stepped read, 4 bytes...     PASS
scanimage: stepped read, 8 bytes...     PASS
scanimage: stepped read, 16 bytes...    PASS
scanimage: stepped read, 32 bytes...    PASS
scanimage: stepped read, 64 bytes...    PASS
scanimage: stepped read, 128 bytes...   PASS
scanimage: stepped read, 256 bytes...   PASS
scanimage: stepped read, 512 bytes...   PASS
scanimage: stepped read, 1024 bytes...  PASS
scanimage: stepped read, 2048 bytes...  PASS
scanimage: stepped read, 2047 bytes...  PASS
scanimage: stepped read, 1023 bytes...  PASS
scanimage: stepped read, 511 bytes...   PASS
scanimage: stepped read, 255 bytes...   PASS
scanimage: stepped read, 127 bytes...   PASS
scanimage: stepped read, 63 bytes...    PASS
scanimage: stepped read, 31 bytes...    PASS
scanimage: stepped read, 15 bytes...    PASS
scanimage: stepped read, 7 bytes...     PASS
scanimage: stepped read, 3 bytes...     PASS

So I tried to scan an A4 page from the command line:

$ scanimage -d pixma:04A9173E_1653C4 -l 0 -t 0 -x 215 -y 297 --resolution 150 --mode Color | convert - scanned-page.png

That worked, so I launched XSane, one of the GUI scanner applications:

$ xsane

That also worked.

Sometimes either scanimage or a GUI scanner application (XSane, gscan2pdf, Simple Scan or whatever) hangs, but, more often than not, scanning now works via the USB connection. However, if either scanimage or a GUI scanner application hangs, I kill them, run them again and then they usually work.

Importantly, printing still works, even though I have changed the USB device group from ‘lp‘ to ‘scanner‘.

So I have satisfied my curiosity and managed to get the MP560 to scan when connected to my laptop via USB, even though it already worked fine when using a network connection instead.

A note on the version of SANE

For information, I currently have Version 1.0.25_pre20150725 (daily snapshot from 25 July 2015) of the package sane-backends installed:

$ eix -I sane-backends
[I] media-gfx/sane-backends
     Available versions:  1.0.24-r5 (~)1.0.25_pre20150628 (~)1.0.25_pre20150725[1] {avahi doc gphoto2 ipv6 snmp systemd threads usb v4l xinetd ABI_MIPS="n32 n64 o32" ABI_PPC="32 64" ABI_S390="32 64" ABI_X86="32 64 x32" SANE_BACKENDS="+abaton +agfafocus +apple +artec +artec_eplus48u +as6e +avision +bh +canon +canon630u +canon_dr -canon_pp +cardscan +coolscan +coolscan2 +coolscan3 +dc210 +dc240 +dc25 +dell1600n_net +dmc +epjitsu +epson +epson2 +fujitsu +genesys +gt68xx +hp +hp3500 +hp3900 +hp4200 +hp5400 +hp5590 +hpljm1005 -hpsj5s +hs2p +ibm +kodak +kodakaio +kvs1025 +kvs20xx kvs40xx +leo +lexmark +ma1509 +magicolor +matsushita +microtek +microtek2 +mustek -mustek_pp +mustek_usb mustek_usb2 +nec +net +niash +p5 +pie +pixma +plustek +plustek_pp -pnm +qcam +ricoh +rts8891 +s9036 +sceptre +sharp +sm3600 +sm3840 +snapscan +sp15c +st400 +stv680 +tamarack +teco1 +teco2 +teco3 +test +u12 +umax +umax1220u +umax_pp +xerox_mfp"}
     Installed versions:  1.0.25_pre20150725[1](01:39:24 25/07/15)(avahi gphoto2 ipv6 usb v4l -doc -snmp -systemd -threads -xinetd ABI_MIPS="-n32 -n64 -o32" ABI_PPC="-32 -64" ABI_S390="-32 -64" ABI_X86="32 64 -x32" SANE_BACKENDS="abaton agfafocus apple artec artec_eplus48u as6e avision bh canon canon630u canon_dr cardscan coolscan coolscan2 coolscan3 dc210 dc240 dc25 dell1600n_net dmc epjitsu epson epson2 fujitsu genesys gt68xx hp hp3500 hp3900 hp4200 hp5400 hp5590 hpljm1005 hs2p ibm kodak kodakaio kvs1025 kvs20xx leo lexmark ma1509 magicolor matsushita microtek microtek2 mustek mustek_usb nec net niash p5 pie pixma plustek plustek_pp qcam ricoh rts8891 s9036 sceptre sharp sm3600 sm3840 snapscan sp15c st400 stv680 tamarack teco1 teco2 teco3 test u12 umax umax1220u umax_pp xerox_mfp -canon_pp -hpsj5s -kvs40xx -mustek_pp -mustek_usb2 -pnm")
     Homepage:            http://www.sane-project.org/
     Description:         Scanner Access Now Easy - Backends

[1] "local_overlay" /usr/local/portage

However, the same symptoms occurred with versions 1.0.24-r5, 1.0.25_pre20150628 and 1.0.25_pre20150725 of the sane-backends package, so I believe the problem was not version-specific.

A note about scanning in Linux
An early developer’s Web site for the SANE pixma backend has the following warning:

If you grant a group a full permission to access the scanner (by using udev, hotplug, resmgr etc.), every members in the group will have full access rights not only for the scanner part but also for the other parts of the device i.e. printer, memory-card reader and fax. These users can bypass your system’s security policy and do everything with the device intentionally and unintentionally.

It is all very well to say that, but it is the only way I could get the backend to work reliably (almost). And, judging by the number of people who posted on the Web that they had to do the same with other Linux distributions, other manufacturers and models of MFPs, this is a common requirement in order to get Linux to work with MFP scanners. It’s not impressive when people have to resort to this to get something to work.

Note that the success of the approach described in this post is dependent on the contents and order of all the UDEV rules files. Just because the rules files I have posted above work in my case does not guarantee they will work in your case too. It depends what rules files your installation already has, what are their precise contents and in what order they are. In my opinion this is not a good concept.

I stand by my comments in the Conclusion of my first post regarding this problem. To have to jump through so many hoops to be able to scan using Linux on a computer connected to a MFP via USB is ridiculous in my opinion. The fact that it works reliably via a network connection does not alter that. I have been ‘scratching an itch’ as I enjoy tinkering, but I feel sorry for users who just need something that works without having to mess around for hours or days.

Background

  1. The problem of scanning using USB multi-function printers in Linux
  2. The problem of scanning using USB multi-function printers in Linux (continued)

The problem of scanning using USB multi-function printers in Linux (continued)

My previous post discussed the inability of the Linux installation on my main laptop to use the scanner of my Canon PIXMA MP560 MFP (multi-function peripheral) when they are connected via USB. Linux sees the MP560 as a single USB device with multiple interfaces: Interface 0 (scanner), Interface 1 (printer) and Interface 2 (USB mass storage). The basic problem seems to be that the usb-storage driver — whether built into the kernel or as an external module — claims the USB device and blocks access by userspace’s libusb, which is what the SANE backend (‘pixma‘, in the case of the MP560) uses to access the USB device. However, scanning works fine when using a network connection instead of the USB connection.

Attempts such as unbinding the usb-storage driver from the USB device — either manually or using a UDEV rule — in order to try and allow libusb/SANE to access the scanner, did not solve the problem. Although I can scan by connecting to the MP560 via my home network, the inability of the OS to scan via the USB interface piqued my interest, so I continued my investigations and below I discuss my latest findings.

Disabling kernel auto-binding

I learned from the interesting blog post Controlling USB device access on Linux how to stop the kernel automatically binding a driver to a USB device in the first place, as distinct from unbinding a driver after the kernel has bound it to a device. I thought this approach could be used to stop the usb-storage driver from binding to the MP560 and thus allow libusb/SANE to access Interface 0. The method using sysfs to stop the kernel binding the driver is to disable kernel USB auto-probing before launching a scanner application, by using the following command:

# echo 0 > /sys/bus/usb/drivers_autoprobe

This did indeed stop the kernel from automatically binding USB drivers to USB devices, but unfortunately libusb/SANE would still not access the MP560 scanner via USB. When drivers_autoprobe contains zero, applications such as XSane can use the network-connected MP560 as before, but still hang if the USB-connected MP560 is selected.

Unloading the usb-storage module

According to various blog and forum posts, some people have been able to use MFP scanners via USB after manually unloading the usb-storage module. I decided to try this. As I had built the kernel with the usb-storage driver internally rather than an external module, I first had to rebuild the kernel with CONFIG_USB_STORAGE=m instead of CONFIG_USB_STORAGE=y. Then I unloaded manually the usb_storage module using the command ‘rmmod usb_storage‘ and launched a scanner application, but the application still hung.

Disabling the usb-storage driver using a ‘quirk’

Then I had a thought: Perhaps there is a kernel ‘quirk’ to disable the usb-storage driver from binding to a specific USB device. Indeed there is (see Kernel Parameters or /usr/src/linux-<version>/Documentation/kernel-parameters.txt).

If the usb-storage driver is built into the kernel (CONFIG_USB_STORAGE=y), I would need to add the following kernel boot parameter to the kernel boot line:

usb-storage.quirks=04a9:173e:i

’04a9′ is the Vendor ID and ‘173e’ is the Product ID of the MP560. The ‘i‘ stands for ‘ignore’.

If the usb-storage driver is built as a kernel module (CONFIG_USB_STORAGE=m), I would need to create a file with a name such as /etc/modprobe.d/usb-storage.conf containing the following line:

options usb-storage quirks=04a9:173e:i

So I set up the quirk. Upon rebooting my laptop, the dmesg command reported the following:

usb 1-1.2.2: new high-speed USB device number 8 using ehci-pci
usb 1-1.2.2: New USB device found, idVendor=04a9, idProduct=173e
usb 1-1.2.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.2.2: Product: MP560 series
usb 1-1.2.2: Manufacturer: Canon
usb 1-1.2.2: SerialNumber: 1653C4
usb-storage 1-1.2.2:1.2: USB Mass Storage device detected
usb-storage 1-1.2.2:1.2: device ignored

Notice the final line. The quirk does indeed cause the usb-storage driver to ignore the MP560.

The lsusb command still shows the device, which is a good sign:

# lsusb
Bus 002 Device 005: ID 0bc2:3300 Seagate RSS LLC
Bus 002 Device 004: ID 0411:01d9 BUFFALO INC. (formerly MelCo., Inc.)
Bus 002 Device 003: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub
Bus 002 Device 002: ID 8087:8000 Intel Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 006: ID 5986:055c Acer, Inc
Bus 001 Device 004: ID 8087:07dc Intel Corp.
Bus 001 Device 007: ID 0603:00f2 Novatek Microelectronics Corp. Keyboard (Labtec Ultra Flat Keyboard)
Bus 001 Device 008: ID 04a9:173e Canon, Inc. MP560
Bus 001 Device 005: ID 045e:00d1 Microsoft Corp. Optical Mouse with Tilt Wheel
Bus 001 Device 003: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub
Bus 001 Device 002: ID 8087:8008 Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

# lsusb -t
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
        |__ Port 2: Dev 3, If 0, Class=Hub, Driver=hub/4p, 480M
            |__ Port 1: Dev 4, If 0, Class=Mass Storage, Driver=usb-storage, 480M
            |__ Port 3: Dev 5, If 0, Class=Mass Storage, Driver=usb-storage, 480M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M
        |__ Port 2: Dev 3, If 0, Class=Hub, Driver=hub/4p, 480M
            |__ Port 1: Dev 5, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
            |__ Port 2: Dev 8, If 0, Class=Vendor Specific Class, Driver=usbfs, 480M
            |__ Port 2: Dev 8, If 1, Class=Printer, Driver=, 480M
            |__ Port 2: Dev 8, If 2, Class=Mass Storage, Driver=, 480M
            |__ Port 4: Dev 7, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
            |__ Port 4: Dev 7, If 1, Class=Human Interface Device, Driver=usbhid, 1.5M
        |__ Port 3: Dev 4, If 0, Class=Wireless, Driver=btusb, 12M
        |__ Port 3: Dev 4, If 1, Class=Wireless, Driver=btusb, 12M
        |__ Port 4: Dev 6, If 0, Class=Video, Driver=uvcvideo, 480M
        |__ Port 4: Dev 6, If 1, Class=Video, Driver=uvcvideo, 480M

The output of the lsusb -v -d 04a9:173e command applicable to the MP560 is as follows:

Bus 001 Device 008: ID 04a9:173e Canon, Inc. MP560
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x04a9 Canon, Inc.
  idProduct          0x173e MP560
  bcdDevice            0.04
  iManufacturer           1 Canon
  iProduct                2 MP560 series
  iSerial                 3 1653C4
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           85
    bNumInterfaces          3
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xc0
      Self Powered
    MaxPower                2mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0 
      bInterfaceProtocol    255 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x07  EP 7 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x88  EP 8 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x89  EP 9 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval              11
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass         7 Printer
      bInterfaceSubClass      1 Printer
      bInterfaceProtocol      2 Bidirectional
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass         8 Mass Storage
      bInterfaceSubClass      6 SCSI
      bInterfaceProtocol     80 Bulk-Only
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x84  EP 4 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x05  EP 5 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
Device Qualifier (for other device speed):
  bLength                10
  bDescriptorType         6
  bcdUSB               2.00
  bDeviceClass            0 
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  bNumConfigurations      1
can't get debug descriptor: Resource temporarily unavailable
Device Status:     0x0001
  Self Powered

The USB device created at boot was as follows:

# ls -la /dev/bus/usb/001/008
crw-rw-r--+ 1 root lp 189, 7 Jul 24 11:01 /dev/bus/usb/001/008

Whether run by the root user or under my user account, the SANE tools detected the MP560 scanner network and USB connections:

$ scanimage -L
device `pixma:MP560_192.168.1.78' is a CANON Canon PIXMA MP560 multi-function peripheral
device `pixma:04A9173E' is a CANON Canon PIXMA MP560 multi-function peripheral

$ sane-find-scanner

  # sane-find-scanner will now attempt to detect your scanner. If the
  # result is different from what you expected, first make sure your
  # scanner is powered up and properly connected to your computer.

  # No SCSI scanners found. If you expected something different, make sure that
  # you have loaded a kernel SCSI driver for your SCSI adapter.

found USB scanner (vendor=0x04a9 [Canon], product=0x173e [MP560 series]) at libusb:001:008
  # Your USB scanner was (probably) detected. It may or may not be supported by
  # SANE. Try scanimage -L and read the backend's manpage.

  # Not checking for parallel port scanners.

  # Most Scanners connected to the parallel port or other proprietary ports
  # can't be detected by this program.

But scanner applications still hung! This time the message displayed by the dmesg command was:

usb 1-1.2.2: usbfs: interface 0 claimed by usbfs while 'scanimage' sets config #1

I unplugged the USB cable and plugged it in again. The output of the dmesg command was:

usb 1-1.2.2: USB disconnect, device number 8
usb 1-1.2.2: new high-speed USB device number 9 using ehci-pci
usb 1-1.2.2: New USB device found, idVendor=04a9, idProduct=173e
usb 1-1.2.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.2.2: Product: MP560 series
usb 1-1.2.2: Manufacturer: Canon
usb 1-1.2.2: SerialNumber: 1653C4
usb-storage 1-1.2.2:1.2: USB Mass Storage device detected
usb-storage 1-1.2.2:1.2: device ignored

I then launched XSane several times and each time I was able to select either the MP560 via my home network (pixma:MP560_192.168.1.78) or via the USB cable (pixma:04A9173E_1653C4) and scan successfully.

By the way, it is possible to scan via the command line instead of using a GUI scanner application. For example, tjhe following command will scan an A4 page via the MP560’s USB connection (see man scanimage for details of the options):

$ scanimage -d pixma:04A9173E_1653C4 -l 0 -t 0 -x 215 -y 297 --resolution 150 --mode Color | convert - scanned-page.png

So the problem is solved, right? Wrong! For whatever reason, scanning via the USB interface is not guaranteed to work every time I boot the laptop. Sometimes scanner applications (and the scanimage command) hang if I select the USB interface; at other times they don’t hang and scanning works fine. If scanning using the USB device is not working, if I unplug and re-insert the USB cable a few times it becomes possible to scan using the USB interface. And once scanning via the USB interface does work, from then onwards it works consistently during that session.

I had been using Version 1.0.24-r5 of the sane-backends package in Gentoo Linux, which is the latest stable version according to the Gentoo package manager. To check if that particular version of the SANE pixma backend might be the cause of the problem I installed the latest version available in the Gentoo package manager (currently 1.0.5_pre20150625). However it made no discernable difference.

To sum up, in my case the most successful approach so far has been to use a kernel ‘quirk’ to force the usb-storage driver to ignore the device and not bind to it. However, this approach does not result in libusb/SANE being able to access the scanner during every boot session, but, if access is successful, it remains successful during the current session. Even if access via the USB interface does not work initially, sometimes I can get it to work by unplugging and re-inserting the USB cable.

UPDATE (July 30, 2015): I have now managed to get scanning to work with almost 100% reliability when connected to the MP560 via USB — see my latest post for details.

The problem of scanning using USB multi-function printers in Linux

Whilst searching the Web I have found many other people experiencing this problem, which I believe happens as a consequence of the way Linux is designed. Basically, if you have a multi-function peripheral that you connect to your computer via USB, the chances are that either scanning or printing will not work. The Web is littered with blog posts, forum threads, mailing list posts and bug reports regarding this phenomenon. There are numerous suggested fixes, usually entailing the addition or modification of udev rules. Sometimes the suggested fixes work; often they don’t. Linux can be a major hassle where peripherals are concerned.

I have a Canon Pixma MP560 MFP (multi-function printer/peripheral), which is a printer, scanner and copier. It also has memory card slots and a USB pen drive socket, to be able to store images directly from the scanner without the need to connect a computer. The MP560 provides two alternative means of connection to a computer: USB and Wi-Fi. I normally connect it via USB to my Clevo W230SS laptop running Gentoo Linux (amd64), but I can also connect it to the laptop via my home Wi-Fi network. Either connection method allows me to print, but I can scan only via the wireless connection.

The dmesg command displays the following messages after I plug a USB cable from the MP560 into my laptop:

usb 1-1.2.2: new high-speed USB device number 8 using ehci-pci
usb 1-1.2.2: New USB device found, idVendor=04a9, idProduct=173e
usb 1-1.2.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.2.2: Product: MP560 series
usb 1-1.2.2: Manufacturer: Canon
usb 1-1.2.2: SerialNumber: 1653C4
usb-storage 1-1.2.2:1.2: USB Mass Storage device detected
scsi host6: usb-storage 1-1.2.2:1.2
scsi 6:0:0:0: Direct-Access     Canon    MP560 series     0104 PQ: 0 ANSI: 2
sd 6:0:0:0: Attached scsi generic sg1 type 0
sd 6:0:0:0: [sdb] Attached SCSI removable disk

Notice that the device also has some internal storage.

The lsusb command shows the device:

$ lsusb
Bus 002 Device 002: ID 8087:8000 Intel Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 006: ID 5986:055c Acer, Inc
Bus 001 Device 004: ID 8087:07dc Intel Corp.
Bus 001 Device 007: ID 0603:00f2 Novatek Microelectronics Corp. Keyboard (Labtec Ultra Flat Keyboard)
Bus 001 Device 009: ID 04a9:173e Canon, Inc. MP560
Bus 001 Device 005: ID 045e:00d1 Microsoft Corp. Optical Mouse with Tilt Wheel
Bus 001 Device 003: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub
Bus 001 Device 002: ID 8087:8008 Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

My Linux user account is in the lp and scanner groups:

$ groups
disk lp wheel floppy uucp cron audio cdrom video games cdrw usb users plugdev crontab wireshark vboxusers scanner fitzcarraldo

The device is in the lp group and I can print without any trouble:

$ ls -la /dev/bus/usb/001/009
crw-rw-r--+ 1 root lp 189, 8 Jun 19 02:55 /dev/bus/usb/001/009

The usblp driver, a common cause of problems with USB printers, does not exist because I purposely did not set CONFIG_USB_PRINTER when I built the kernel, specifically to avoid such problems:

$ grep CONFIG_USB_PRINTER /usr/src/linux/.config
# CONFIG_USB_PRINTER is not set

so, obviously, the usblp driver is neither built into the kernel nor compiled as a module:

$ lsmod | grep usb
btusb                  22292  0
bluetooth             281605  27 bnep,hidp,btusb,rfcomm

I have the latest stable versions of the udev-related packages installed (as you can see below, I use eudev instead of udev):

$ eix -I udev
[I] dev-python/pyudev
     Available versions:  0.16.1-r1 {pygobject pyqt4 pyside test PYTHON_TARGETS="python2_7 python3_3 python3_4"}
     Installed versions:  0.16.1-r1(03:32:17 18/04/15)(pyqt4 -pygobject -pyside -test PYTHON_TARGETS="python2_7 python3_3 -python3_4")
     Homepage:            http://pyudev.readthedocs.org https://github.com/pyudev/pyudev
     Description:         Python binding to libudev

[I] sys-fs/eudev
     Available versions:  *1.3 *1.5.3-r1 1.9-r2 1.10-r2 ~2.1.1 ~3.0 3.1.2 ~3.1.2-r10 **9999 {doc gudev (+)hwdb introspection (+)keymap (+)kmod +modutils +openrc +rule-generator selinux static-libs test ABI_MIPS="n32 n64 o32" ABI_PPC="32 64" ABI_S390="32 64" ABI_X86="32 64 x32"}
     Installed versions:  3.1.2(19:44:12 16/07/15)(gudev hwdb introspection kmod -doc -selinux -static-libs -test ABI_MIPS="-n32 -n64 -o32" ABI_PPC="-32 -64" ABI_S390="-32 -64" ABI_X86="32 64 -x32")
     Homepage:            https://github.com/gentoo/eudev
     Description:         Linux dynamic and persistent device naming support (aka userspace devfs)

[I] sys-fs/udev-init-scripts
     Available versions:  27^t [M]~29^t ~30^t **9999^t
     Installed versions:  27^t(05:29:06 09/04/15)
     Homepage:            http://www.gentoo.org
     Description:         udev startup scripts for openrc

[I] virtual/libgudev
     Available versions:  215-r1(0/0) 215-r2(0/0) 215-r3(0/0) ~230(0/0) {introspection static-libs systemd ABI_MIPS="n32 n64 o32" ABI_PPC="32 64" ABI_S390="32 64" ABI_X86="32 64 x32"}
     Installed versions:  215-r3(10:18:16 11/06/15)(introspection -static-libs -systemd ABI_MIPS="-n32 -n64 -o32" ABI_PPC="-32 -64" ABI_S390="-32 -64" ABI_X86="64 -32 -x32")
     Description:         Virtual for libgudev providers

[I] virtual/libudev
     Available versions:  215-r1(0/1) {static-libs systemd ABI_MIPS="n32 n64 o32" ABI_PPC="32 64" ABI_S390="32 64" ABI_X86="32 64 x32"}
     Installed versions:  215-r1(17:51:42 18/04/15)(-static-libs -systemd ABI_MIPS="-n32 -n64 -o32" ABI_PPC="-32 -64" ABI_S390="-32 -64" ABI_X86="32 64 -x32")
     Description:         Virtual for libudev providers

[I] virtual/udev
     Available versions:  215 ~217 {systemd}
     Installed versions:  215(05:28:55 09/04/15)(-systemd)
     Description:         Virtual to select between different udev daemon providers

Found 6 matches.

I have the latest stable SANE-related packages installed:

$ eix -I sane
[I] dev-perl/Sane
     Available versions:  (~)0.50.0-r1 {test}
     Installed versions:  0.50.0-r1(17:39:10 23/06/15)(-test)
     Homepage:            http://search.cpan.org/dist/Sane/
     Description:         The Sane module allows you to access SANE-compatible scanners in a Perl

[I] kde-apps/ksaneplugin
     Available versions:  (4) 4.14.3(4/4.14)
       {aqua debug}
     Installed versions:  4.14.3(4)(14:13:01 17/04/15)(-aqua -debug)
     Homepage:            http://www.kde.org/
     Description:         SANE Plugin for KDE

[I] kde-apps/libksane
     Available versions:  (4) 4.14.3(4/4.14)
       {aqua debug}
     Installed versions:  4.14.3(4)(13:55:44 17/04/15)(-aqua -debug)
     Homepage:            http://www.kde.org/
     Description:         SANE Library interface for KDE

[I] media-gfx/sane-backends
     Available versions:  1.0.24-r5 ~1.0.25_pre20150628 {avahi doc gphoto2 ipv6 snmp systemd threads usb v4l xinetd ABI_MIPS="n32 n64 o32" ABI_PPC="32 64" ABI_S390="32 64" ABI_X86="32 64 x32" SANE_BACKENDS="+abaton +agfafocus +apple +artec +artec_eplus48u +as6e +avision +bh +canon +canon630u +canon_dr -canon_pp +cardscan +coolscan +coolscan2 +coolscan3 +dc210 +dc240 +dc25 +dell1600n_net +dmc +epjitsu +epson +epson2 +fujitsu +genesys +gt68xx +hp +hp3500 +hp3900 +hp4200 +hp5400 +hp5590 +hpljm1005 -hpsj5s +hs2p +ibm +kodak +kodakaio +kvs1025 +kvs20xx kvs40xx +leo +lexmark +ma1509 +magicolor +matsushita +microtek +microtek2 +mustek -mustek_pp +mustek_usb mustek_usb2 +nec +net +niash +p5 +pie +pixma +plustek +plustek_pp -pnm +qcam +ricoh +rts8891 +s9036 +sceptre +sharp +sm3600 +sm3840 +snapscan +sp15c +st400 +stv680 +tamarack +teco1 +teco2 +teco3 +test +u12 +umax +umax1220u +umax_pp +xerox_mfp"}
     Installed versions:  1.0.24-r5(17:55:11 18/04/15)(avahi gphoto2 ipv6 usb v4l -doc -snmp -systemd -threads -xinetd ABI_MIPS="-n32 -n64 -o32" ABI_PPC="-32 -64" ABI_S390="-32 -64" ABI_X86="32 64 -x32" SANE_BACKENDS="abaton agfafocus apple artec artec_eplus48u as6e avision bh canon canon630u canon_dr cardscan coolscan coolscan2 coolscan3 dc210 dc240 dc25 dell1600n_net dmc epjitsu epson epson2 fujitsu genesys gt68xx hp hp3500 hp3900 hp4200 hp5400 hp5590 hpljm1005 hs2p ibm kodak kodakaio kvs1025 kvs20xx leo lexmark ma1509 magicolor matsushita microtek microtek2 mustek mustek_usb nec net niash p5 pie pixma plustek plustek_pp qcam ricoh rts8891 s9036 sceptre sharp sm3600 sm3840 snapscan sp15c st400 stv680 tamarack teco1 teco2 teco3 test u12 umax umax1220u umax_pp xerox_mfp -canon_pp -hpsj5s -kvs40xx -mustek_pp -mustek_usb2 -pnm")
     Homepage:            http://www.sane-project.org/
     Description:         Scanner Access Now Easy - Backends

[I] media-gfx/sane-frontends
     Available versions:  1.0.14 {gimp}
     Installed versions:  1.0.14(19:47:50 18/06/15)(gimp)
     Homepage:            http://www.sane-project.org
     Description:         Scanner Access Now Easy

[I] media-gfx/xsane
     Available versions:  0.999-r1 {gimp jpeg lcms nls ocr png tiff}
     Installed versions:  0.999-r1(12:03:12 19/04/15)(gimp jpeg lcms nls png tiff -ocr)
     Homepage:            http://www.xsane.org/
     Description:         graphical scanning frontend

Found 6 matches.

The following SANE backends were installed when I installed SANE:

$ ls -F1 /etc/sane.d/ | columns -c 3 -w 20
abaton.conf         agfafocus.conf      apple.conf
artec.conf          artec_eplus48u.conf avision.conf
bh.conf             canon.conf          canon630u.conf
canon_dr.conf       cardscan.conf       coolscan.conf
coolscan2.conf      coolscan3.conf      dc210.conf
dc240.conf          dc25.conf           dell1600n_net.conf
dll.conf            dll.d/              dmc.conf
epjitsu.conf        epson.conf          epson2.conf
fujitsu.conf        genesys.conf        gphoto2.conf
gt68xx.conf         hp.conf             hp3900.conf
hp4200.conf         hp5400.conf         hs2p.conf
ibm.conf            kodak.conf          kodakaio.conf
leo.conf            lexmark.conf        ma1509.conf
magicolor.conf      matsushita.conf     microtek.conf
microtek2.conf      mustek.conf         mustek_usb.conf
nec.conf            net.conf            p5.conf
pie.conf            pixma.conf          plustek.conf
plustek_pp.conf     qcam.conf           ricoh.conf
rts8891.conf        s9036.conf          saned.conf
sceptre.conf        sharp.conf          sm3840.conf
smfp.conf           snapscan.conf       sp15c.conf
st400.conf          stv680.conf         tamarack.conf
teco1.conf          teco2.conf          teco3.conf
test.conf           u12.conf            umax.conf
umax1220u.conf      umax_pp.conf        v4l.conf
xerox_mfp.conf

I checked all the SANE backend configuration files, and none of them mention the MP560 (I was not expecting them to mention it, as, according to man sane-pixma, the pixma backend detects Canon PIXMA USB devices automatically):

$ grep -rnwi /etc/sane.d/ -e "173e"
$

The SANE file dll.conf does list the pixma backend configuration file which is only for declaring networked Canon PIXMA devices, as the pixma backend detects Canon USB devices automatically):

$ grep pixma /etc/sane.d/dll.conf
pixma

$ cat /etc/sane.d/pixma.conf
# pixma.conf configuration for the sane pixma backend
#
# define URI's of scanners (one per line)
# This is only used for network scanners.
# normally scanners will be detected by sending a broadcast
# if this does not work under your OS, or if the scanners
# are on a different subnet, configure your scanners URI here
#
# method must be bjnp
# port number can normally be left out, port 8612 is used as default
# Example:
# bjnp://myscanner.my.domain:8612
# bjnp://printer-1.pheasant.org
#

I don’t think it is even used these days, but the file /etc/hotplug/usb/libsane.usermap already includes the device:

# Canon PIXMA MP560
libusbscanner 0x0003 0x04a9 0x173e 0x0000 0x0000 0x00 0x00 0x00 0x00 0x00 0x00 0x00000000

The file /lib64/udev/rules.d/41-libsane.rules already includes the device:

# Canon PIXMA MP560
ATTRS{idVendor}=="04a9", ATTRS{idProduct}=="173e", MODE="0664", GROUP="scanner", ENV{libsane_matched}="yes"

However, scanning from Linux via USB is a troubled affair. Very occasionally the scanner application (XSane, Simple Scan, gscan2pdf, or whatever) will launch and the scanner works, but usually the scanner application just hangs and the dmesg command shows one or more error messages such as the following:

usb 1-1.2.2: usbfs: interface 2 claimed by usb-storage while 'xsane' sets config #1

usb 1-1.2.2: usbfs: interface 2 claimed by usb-storage while 'gscan2pdf' sets config #1

I have USB mass storage support enabled in the kernel so that my laptop can access external USB mass storage devices:

$ grep CONFIG_USB_STORAGE= /usr/src/linux/.config
CONFIG_USB_STORAGE=y

As the three interfaces (printer, scanner and internal storage) are all accessed as a single USB device (/dev/bus/usb/001/009, or whatever), there appears to be a conflict between the kernel claiming the MFP’s internal mass storage and SANE trying to access the scanner. I do not want to disable the kernel’s USB mass storage support (not even by rebuilding the kernel with CONFIG_USB_STORAGE=m and temporarily unloading manually the usb-storage module, as some people suggest), as I would not be able to access my external USB mass storage devices.

The scanimage and sane-find-scanner utilities detect the scanner correctly via USB:

$ scanimage -L
device `v4l:/dev/video0' is a Noname BisonCam, NB Pro virtual device
device `pixma:04A9173E_1653C4' is a CANON Canon PIXMA MP560 multi-function peripheral

(The BisonCam is the Webcam built into my laptop.)

$ sane-find-scanner

  # sane-find-scanner will now attempt to detect your scanner. If the
  # result is different from what you expected, first make sure your
  # scanner is powered up and properly connected to your computer.

  # No SCSI scanners found. If you expected something different, make sure that
  # you have loaded a kernel SCSI driver for your SCSI adapter.

found USB scanner (vendor=0x04a9 [Canon], product=0x173e [MP560 series]) at libusb:001:009
  # Your USB scanner was (probably) detected. It may or may not be supported by
  # SANE. Try scanimage -L and read the backend's manpage.

  # Not checking for parallel port scanners.

  # Most Scanners connected to the parallel port or other proprietary ports
  # can't be detected by this program.

  # You may want to run this program as root to find all devices. Once you
  # found the scanner devices, be sure to adjust access permissions as
  # necessary.

The scanimage test commands do not indicate any problem:

$ scanimage -d test -T
scanimage: scanning image of size 157x196 pixels at 8 bits/pixel
scanimage: acquiring gray frame, 8 bits/sample
scanimage: reading one scanline, 157 bytes...   PASS
scanimage: reading one byte...          PASS
scanimage: stepped read, 2 bytes...     PASS
scanimage: stepped read, 4 bytes...     PASS
scanimage: stepped read, 8 bytes...     PASS
scanimage: stepped read, 16 bytes...    PASS
scanimage: stepped read, 32 bytes...    PASS
scanimage: stepped read, 64 bytes...    PASS
scanimage: stepped read, 128 bytes...   PASS
scanimage: stepped read, 256 bytes...   PASS
scanimage: stepped read, 255 bytes...   PASS
scanimage: stepped read, 127 bytes...   PASS
scanimage: stepped read, 63 bytes...    PASS
scanimage: stepped read, 31 bytes...    PASS
scanimage: stepped read, 15 bytes...    PASS
scanimage: stepped read, 7 bytes...     PASS
scanimage: stepped read, 3 bytes...     PASS

$ scanimage -d pixma -T
scanimage: scanning image of size 638x877 pixels at 24 bits/pixel
scanimage: acquiring RGB frame, 8 bits/sample
scanimage: reading one scanline, 1914 bytes...  PASS
scanimage: reading one byte...          PASS
scanimage: stepped read, 2 bytes...     PASS
scanimage: stepped read, 4 bytes...     PASS
scanimage: stepped read, 8 bytes...     PASS
scanimage: stepped read, 16 bytes...    PASS
scanimage: stepped read, 32 bytes...    PASS
scanimage: stepped read, 64 bytes...    PASS
scanimage: stepped read, 128 bytes...   PASS
scanimage: stepped read, 256 bytes...   PASS
scanimage: stepped read, 512 bytes...   PASS
scanimage: stepped read, 1024 bytes...  PASS
scanimage: stepped read, 2048 bytes...  PASS
scanimage: stepped read, 2047 bytes...  PASS
scanimage: stepped read, 1023 bytes...  PASS
scanimage: stepped read, 511 bytes...   PASS
scanimage: stepped read, 255 bytes...   PASS
scanimage: stepped read, 127 bytes...   PASS
scanimage: stepped read, 63 bytes...    PASS
scanimage: stepped read, 31 bytes...    PASS
scanimage: stepped read, 15 bytes...    PASS
scanimage: stepped read, 7 bytes...     PASS
scanimage: stepped read, 3 bytes...     PASS

As mentioned earlier, the udev/eudev rules file appears to contain a valid rule for the scanner:

# Canon PIXMA MP560
ATTRS{idVendor}=="04a9", ATTRS{idProduct}=="173e", MODE="0664", GROUP="scanner", ENV{libsane_matched}="yes"

Notice the rule assigns the device’s group to be ‘scanner‘, not ‘lp‘, although changing the group assignment to ‘lp‘ in the rule makes no discernable difference to the scanning problem in my case. As the device’s group is actually ‘lp‘, I assume another rule overrides this rule, but I have no idea which rule it is and in which rules file it occurs.

Occasionally I am lucky and scanning does work, but, more often than not, scanner applications cannot access the scanner and just hang.

A work-around if the peripheral also has a network interface

I configured my home network router always to use the IP address 192.168.1.78 for the MP560 and I added the following line to the file /etc/sane.d/pixma.conf in order to be able to scan via Wi-Fi instead of USB (I have the package cups-bjnp installed for printing purposes, but I am not sure if that package is also needed by SANE in this case):

bjnp://192.168.1.78

With the above line added to /etc/sane.d/pixma.conf the scanimage utility detects the scanner correctly via both the Wi-Fi connection and the USB interface:

$ scanimage -L
device `v4l:/dev/video0' is a Noname BisonCam, NB Pro virtual device
device `pixma:MP560_192.168.1.78' is a CANON Canon PIXMA MP560 multi-function peripheral
device `pixma:04A9173E_1653C4' is a CANON Canon PIXMA MP560 multi-function peripheral

So, as I usually cannot get scanning to work via USB, I can scan via Wi-Fi instead. It’s a work-around, not a solution, but at least by doing that I can scan reliably as well as print. Of course you can’t use such a work-around if you have a model of MFP that only provides a USB connection.

Failed experiments

Experiment 1

I also tried unbinding the usb-storage driver from the usb device:

# ls /sys/bus/usb/drivers
btusb hub usb usb-storage usbfs usbhid uvcvideo
# ls /sys/bus/usb/drivers/btusb/
1-1.3:1.0 1-1.3:1.1 bind module new_id remove_id uevent unbind
# ls /sys/bus/usb/drivers/hub
1-0:1.0 1-1.2:1.0 1-1:1.0 2-0:1.0 2-1:1.0 bind module new_id remove_id uevent unbind
# ls /sys/bus/usb/drivers/usb
1-1 1-1.2 1-1.2.1 1-1.2.2 1-1.2.4 1-1.3 1-1.4 2-1 bind uevent unbind usb1 usb2
# ls /sys/bus/usb/drivers/usb-storage/
1-1.2.2:1.2 bind module new_id remove_id uevent unbind
# ls /sys/bus/usb/drivers/usbfs
bind module new_id remove_id uevent unbind
# ls /sys/bus/usb/drivers/usbhid
1-1.2.1:1.0 1-1.2.4:1.0 1-1.2.4:1.1 bind module new_id remove_id uevent unbind
# ls /sys/bus/usb/drivers/uvcvideo
1-1.4:1.0 1-1.4:1.1 bind module new_id remove_id uevent unbind
# tree /sys/bus/usb/drivers/usb-storage/
/sys/bus/usb/drivers/usb-storage/
├── 1-1.2.2:1.2 -> ../../../../devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2.2/1-1.2.2:1.2
├── bind
├── module -> ../../../../module/usb_storage
├── new_id
├── remove_id
├── uevent
└── unbind

2 directories, 5 files
# echo -n "1-1.2.2:1.2" > /sys/bus/usb/drivers/usb-storage/unbind
# tree /sys/bus/usb/drivers/usb-storage/
/sys/bus/usb/drivers/usb-storage/
├── bind
├── module -> ../../../../module/usb_storage
├── new_id
├── remove_id
├── uevent
└── unbind

1 directory, 5 files
# tree /sys/bus/usb/devices/1-1.2.2:1.2
/sys/bus/usb/devices/1-1.2.2:1.2
├── bAlternateSetting
├── bInterfaceClass
├── bInterfaceNumber
├── bInterfaceProtocol
├── bInterfaceSubClass
├── bNumEndpoints
├── ep_05
│   ├── bEndpointAddress
│   ├── bInterval
│   ├── bLength
│   ├── bmAttributes
│   ├── direction
│   ├── interval
│   ├── power
│   ├── type
│   ├── uevent
│   └── wMaxPacketSize
├── ep_84
│   ├── bEndpointAddress
│   ├── bInterval
│   ├── bLength
│   ├── bmAttributes
│   ├── direction
│   ├── interval
│   ├── power
│   ├── type
│   ├── uevent
│   └── wMaxPacketSize
├── modalias
├── power
├── subsystem -> ../../../../../../../../bus/usb
├── supports_autosuspend
└── uevent

6 directories, 27 files

After unbinding the usb-storage driver from the USB device, no more messages such as ‘usbfs: interface 2 claimed by usb-storage while 'xsane' sets config #1‘ are added to /var/log/messages when I launch a scanner application and select the USB device, but the scanner application still hangs (e.g. the XSane windows do not appear until I switch off the MP560 or unplug the USB cable). This happens irrespective of whether the USB device permissions are:

# ls -la /dev/bus/usb/001/009
crw-rw-r--+ 1 root lp 189, 8 Jul 20 20:35 /dev/bus/usb/001/009

or:

# ls -la /dev/bus/usb/001/009
crw-rw-r--+ 1 fitzcarraldo lp 189, 8 Jul 20 20:35 /dev/bus/usb/001/009

or:

# ls -la /dev/bus/usb/001/009
crw-rw-r--+ 1 fitzcarraldo scanner 189, 8 Jul 20 20:51 /dev/bus/usb/001/009

To reiterate, neither unbinding the usb-storage driver from the USB device first nor changing the owner and group of the USB device solves the problem. So possibly the problem is not caused by udev or by a USB driver, but by the SANE software.

Experiment 2

I found a thread in the SANE developers’ mailing list about the same problem with a different model of MFP: Help needed diagnosing strange failure to scan with Samsung SCX-4500W. The same user posted the same query in the Arch Linux forums: [SOLVED] Samsung SCX4500W MFP can’t get scanner to work. Like my Canon PIXMA MP560, that MFP has more than one interface in a single USB device. Notice in the Arch Linux thread that the user never found a solution and finally adopted the same work-around I use, namely to scan via a network interface rather than via the USB interface.

Theodore Kilgore gives a good explanation in that SANE developers’ mailing list thread of why the problem occurs in Linux, and Thorsten Müller’s post suggests a udev rule that sets the permissions for the MFP so that SANE, CUPS and logged-in users can all access the USB device. All I had to do was replace references to Samsung (such as the vendor ID and product ID) with those for my Canon PIXMA MP560. I left everything else in my installation exactly the way it was (for example I did not touch /lib64/udev/rules.d/41-libsane.rules and /lib64/udev/rules.d/70-printers.rules). The only thing I did was to add a udev rules file /etc/udev/rules.d/99-canon-mp560.rules with the following contents:

# ACL settings for Canon PIXMA MP560 printer MFP
ATTR{idVendor}=="04a9", ATTR{idProduct}=="173e", GOTO="canon"
GOTO="canon_end"

LABEL="canon"
RUN+="/bin/setfacl -m g:scanner:rw -m g:lp:rw $env{DEVNAME}"
TEST=="/var/run/ConsoleKit/database", \
        RUN+="udev-acl --action=$env{ACTION} --device=$env{DEVNAME}"

LABEL="canon_end"

Both /bin/setfacl and /var/run/ConsoleKit/database exist in my installation, and, as shown earlier, my user account is a member of both the lp and scanner groups. After adding the above file, I rebooted and it appears the rule works as intended:

# getfacl /dev/bus/usb/001/009
getfacl: Removing leading '/' from absolute path names
# file: dev/bus/usb/001/009
# owner: root
# group: lp
user::rw-
user:fitzcarraldo:rw-
group::rw-
group:lp:rw-
group:scanner:rw-
mask::rw-
other::r--

However, although I was still able to print I still could not scan. Mind you, the line beginning ‘TEST==‘ in the file /etc/udev/rules.d/99-canon-mp560.rules is also in the file /lib64/udev/rules.d/70-udev-acl.rules, but I’m no expert in udev rules, which are frankly beyond the ability of most users.

Experiment 3

I found a blog post about the same problem but with a Canon MP210 MFP: Canon multifunction printer: getting the printer drivers and scanner to work in debian/ubuntu/mint. This post suggested creating a udev rule file /etc/udev/rules.d/40-scanner-permissions.rules containing the following:

# usb scanner
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", MODE:="0666"
SUBSYSTEM=="usb_device",MODE:="0666"

but, although the rule appears to work as intended, it is still not possible to scan in my case. I then changed the file name to /etc/udev/rules.d/95-scanner-permissions.rules, but that made no difference in my case.

Experiment 4

I also tried changing MODE="0664" to MODE="0666" in the following line in the file /lib64/udev/rules.d/50-udev-default.rules but that made no difference either:

SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", MODE="0664"

Experiment 5

I am able to change the group of the USB device to ‘scanner‘ instead of ‘lp‘ by adding a rules file /lib64/udev/rules.d/99-canon.rules (apparently 41-libsane.rules does not work as intended because it is overruled by a higher-numbered file, but I have no idea which one, as 41-libsane.rules is the only one explicitly mentioning the MP560) containing the following:

ATTRS{idVendor}=="04a9", ATTRS{idProduct}=="173e", MODE="0664", GROUP="scanner", ENV{libsane_matched}="yes"

But scanning still does not work, whether or not I unbind the usb-storage driver from the USB device first and whether or not I change the owner and group of the USB device to root:lp, root:scanner, fitzcarraldo:lp or fitzcarraldo:scanner.

Conclusion

Although my installation can print via USB, scanning via USB does not work, whether or not the usb-storage driver is bound to the USB device and whoever is the owner and group of the USB device. So it could be that the problem is not caused by udev or by the kernel (a USB driver), but by the SANE software itself. However, I think it is more likely to be some sort of contention between kernel and userspace, despite unbinding the usb-storage driver from the device. Although I’m not excluding the possibility of a bug in SANE, irrespective of that it seems to me that the way GNU/Linux handles multiple interfaces of a single USB device is flawed. The udev design results in a morass of confusing and potentially conflicting rules in umpteen files in different directories, and the apparently uncoordinated independent demands on the same USB interface by the kernel and userspace are another potential source of problems. There is no standardisation in the udev rules files and their contents between the different Linux distributions, making investigation and solution of such problems even more complicated. Having to resort to work-arounds such as scanning via a network interface or scanning to a USB pen drive or memory card is a poor way of circumventing the problem, and is of no help anyway if a multi-function peripheral does not have a network interface, pen drive socket or memory card slot.

UPDATE (July 24, 2015): I have tried some other approaches, and had more success using a ‘quirk’ for the usb-storage driver — see my next post for details.

Addendum: How to stop scanning applications detecting a Webcam

By the way, to stop XSane and other scanning applications detecting my Webcam via the Video for Linux SANE backend, I commented out all the device lines in the file /etc/sane.d/v4l.conf like so:

$ cat
# In order to use the v4linux backend you have to give the device
# You can enable multiple lines if
# you really have multible v4l devices.
#
#/dev/bttv0
#/dev/video0
#/dev/video1
#/dev/video2
#/dev/video3

Using a Samsung Xpress C460FW with Gentoo Linux and Android KitKat for printing and scanning

INTRODUCTION

A work colleague has just received a Samsung Xpress C460FW MFP (laser printer, scanner, copier and fax machine) for small print jobs. It is possible to connect to it via USB, Direct USB, wired network, wireless network, Wi-Fi Direct and NFC; that’s impressive for a MFP that can be purchased for GBP 270 in the UK.

I wanted to use the C460FW to print and scan from my laptop running Gentoo Linux, and also to print and scan from my Samsung Galaxy Note 4 running Android KiKat. It turned out that I was able to do all of those, and it was not difficult to set up.

A technician from the IT Support department had already entered a static IP address, subnet mask and default gateway IP address via the C460FW’s control panel to connect it to the office’s wired network. So my options to connect to this particular C460FW are: the wired network for Linux; Wi-Fi Direct for Linux and Android; NFC for Android.

I had never used Wi-Fi Direct before, but it turned out to be easy in Gentoo Linux on my laptop, and also easy in Android KitKat on my Samsung Galaxy Note 4. I had never used NFC before either, and that also turned out to be easy on my Samsung Galaxy Note 4.

Samsung has a series of videos on YouTube explaining how to use Wi-Fi Direct and NFC for printing, scanning and faxing with the C460FW from a Samsung smartphone; here are links to a few of them:

Samsung Smart Printing – 01 NFC Connect

Samsung Smart Printing – 02 Wi Fi Direct

Samsung Smart Printing – 03 Wi Fi

Samsung Smart Printing – 04 NFC Print

Samsung Smart Printing – 05 NFC Scan

Samsung Smart Printing – 06 NFC Fax

Samsung Smart Printing – 11 Samsung Mobile Print App(Printer Status)

PRINTING

Linux

Wired connection

I had installed the package net-print/samsung-unified-linux-driver Version 1.02 from a Portage local overlay back in March 2013 when I needed to print to a different model of Samsung MFP, so I thought I would see if that driver would work with the C460FW. I opened the CUPS Printer Manager in a browser window (http://localhost:631/) to configure my Gentoo installation to print to the device via the wired network. ‘Samsung C460 Series‘ was in the list of discovered network printers in the CUPS Printer Manager, and the driver ‘Samsung C460 Series PS‘ was displayed at the top of the list of models, so it was a piece of cake to set up the printer via CUPS, and I was able to print a test page in no time at all. My colleague uses a laptop running Windows 7, and he had to install the Windows driver from a Samsung CD that came with the C460FW.

Wireless connection

As the IT Support technician had configured the C460FW to print via the office wired network rather than the office wireless network, I decided to configure my laptop to print via Wi-Fi Direct, just to learn about Wi-Fi Direct, really. On the C460FW’s control panel I selected Network > Wireless > Wi-Fi Direct and enabled Wi-Fi Direct. Scrolling through the Wi-Fi Direct entries in the LCD I saw the following information:

Device Name: C460 Series
Network Key: <an 8-digit code>
IP address: 192.168.003.001

Two new networks were listed under ‘Available connections’ in plasma-nm (the KDE GUI front-end to NetworkManager) on my laptop: ‘DIRECT-HeC460 Series‘ and ‘DIRECT-SqC460 Series‘, both using WPA2-PSK encryption. I used the control panel of the C460FW to print a network configuration report in order to check which of the two SSIDs I should select, and it is ‘DIRECT-HeC460 Series‘ (I found out later that an adjacent room also has a C460FW and its Wi-Fi Direct SSID is ‘DIRECT-SqC460 Series‘). So I selected ‘DIRECT-HeC460 Series‘ and plasma-nm prompted me to enter a network password. I entered the 8-digit key I had found from the C460FW’s LCD panel (it’s also listed in the printed network configuration report), and NetworkManager connected to the printer.

In exactly the same way as I do when setting up any printer in Linux, I launched Firefox, opened the CUPS Printer Manager page, clicked on ‘Administration’ > ‘Add Printer’ and entered the user name ‘root’ and the password in the pop-up window. Again the ‘Add Printer’ page had ‘Samsung C460 Series‘ in the list of discovered network printers, so I just selected it and clicked on ‘Continue’. As I had already set up the printer in CUPS for the wired network connection and given it the name ‘Samsung_C460FW_office‘, I entered the name ‘Samsung_C460FW_office_WiFi_Direct‘ to distinguish it from the wired network entry, entered a Description and Location, and clicked on ‘Continue’. The next page had ‘Samsung C460 Series PS‘ first in the driver list so I selected that, clicked on ‘Add Printer’ and that was it. I was able to print a test page from the CUPS Printer Manager, and the printer is now included the list of printers in Linux applications’ print dialogues.

When I want to print using Wi-Fi Direct the only thing I need to remember to do first is select ‘DIRECT-HeC460 Series‘ in the network GUI on the KDE Panel, so that the connection is active when I click ‘Print’ in whichever application I want to print from.

Given the ease of printing via the wired network and Wi-Fi Direct, I have no doubts that printing would also work had the C460FW been configured for the office wireless network instead of the wired network.

Duplex printing

The only downside to the Samsung Xpress C460FW is that it only supports manual duplex printing. If you specify duplex printing when printing from Windows, Samsung’s Windows driver prints all the odd-numbered pages in reverse order and displays a message in Windows telling you what to do next (turn over the pile of paper and put it back in the paper tray!), but in Linux it’s not difficult to work out what you have to do: you simply have to print all the odd-numbered sides first, turn over the paper, then print all the even-numbered sides. The print dialogue in Linux applications gives you the option to print only odd-numbered pages or only even-numbered pages, so there is no problem. The print dialogue in some Linux applications allows you to print pages in reverse order as well but, if not, you have to reverse the order yourself before printing the even-numbered pages (i.e. put Page 1 face down at the top of the pile then Page 3 face down under it, and so on). It’s not a big deal unless the document has a large number of pages.

Android

As you would expect with devices from the same manufacturer, setting up my Samsung Galaxy Note 4 to print with the Samsung Xpress C460FW via WPS (Wi-Fi Protected Setup) was easy. When I selected ‘Print’ on the Galaxy Note 4, it gave me the option to print via wireless network or Wi-Fi Direct. I chose the latter and, as I had already enabled Wi-Fi Direct on the C460FW’s control panel, the printer name was displayed in the list of available devices. I selected it, a blue LED began flashing on the C460FW’s control panel and the LCD prompted me to press the WPS button (on the left of the control panel). As soon as I pressed that, the C460FW printed the document sent by my Galaxy Note 4. From then onwards, I just needed to select ‘Print’ on the Galaxy Note 4, select the printer from the list of available devices, and the document is printed. When I want to print using Wi-Fi Direct the only thing I need to remember to do first on the Galaxy Note 4 is select ‘DIRECT-HeC460 Series‘ as the Wi-Fi network.

NFC

I then decided to try to print using NFC. I placed the Galaxy Note 4, without Wi-Fi enabled and with the Home Screen displayed (not the Lock Screen), on the NFC label on top of the C460FW; Android launched Play Store and prompted me to install Samsung Mobile Print, which I did. Now when I place the Galaxy Note 4 on the NFC label, the Galaxy Note 4 automatically enables Wi-Fi, connects to the C460FW directly and displays the Mobile Print app showing the options Print, Scan and Fax, and a page of icons labelled: Gallery, Camera, Google Drive, E-mail, Web page, Document, Facebook, DropBox, Evernote, OneDrive and Box, as well as a Settings icon to configure the printer (paper size etc.). I am able to select a document, photograph, Web page, etc. on the Galaxy Note 4 and print it. It is also possible to launch the Mobile Print app first and then place the Galaxy Note 4 on the C460FW.

NFC is not entirely trouble-free, though. Sometimes the Galaxy Note 4 displays a ‘Device not found‘ message but I can still print. Sometimes the Galaxy Note 4 displays the message ‘Connecting printer. There was some error while connecting to this device. Check your printer and try again. If NFC Pin was changed then please enter new NFC Pin.‘ and the two devices will not connect. Powering off then on the C460FW solves that. Sometimes the Galaxy Note 4 connects to another wireless network instead of to the C460FW via Wi-Fi Direct and the Samsung Galaxy Note 4 then has to disconnect automatically from the other network. Sometimes the C460FW prompts me to press its WPS button and the Galaxy Note 4 then connects via Wi-Fi Direct but the Mobile Print app then displays the error message ‘Device not found. To troubleshoot please check – C460 Series is powered on. – Wi-Fi direct is enabled on C460 Series. – C460 Series and Mobile are connected to the same network.‘. Again, powering off then on the C460FW solves that. Despite these hiccups, printing via NFC is still handy.

SCANNING

Linux

I found out how to get the C460FW scanner working by consulting the third-party Web site The Samsung Unified Linux Driver Repository which someone created to provide .deb packages for the Samsung driver as well as tips on how to get Samsung printers and scanners working in Linux. It turned out to be relatively straightforward to scan, both via the office wired network and via Wi-Fi Direct. I edited the file /etc/sane.d/xerox_mfp.conf and replaced the following:

#Samsung C460 Series
usb 0x04e8 0x3468

with the following in order to use the C460FW to scan via the office wired network:

#Samsung C460 Series
#usb 0x04e8 0x3468
#Wired network static address of this C460FW:
tcp 10.90.21.125

or with the following in order to use the C460FW to scan via Wi-Fi Direct:

#Samsung C460 Series
#usb 0x04e8 0x3468
#Wi-Fi Direct address of this C460FW:
tcp 192.168.3.1

I found the IP addresses from the network configuration report I printed earlier.

I was able to use the two Linux scanning applications I normally use, XSane and gscan2pdf, to scan via the wired network and via Wi-Fi Direct. The resulting scans were very good. Given the ease of scanning via the wired network and Wi-Fi Direct, I have no doubts that scanning would work via a wireless network had the C460FW been configured for the office wireless network instead of the wired network.

Android

To use NFC to scan a document I place the Galaxy Note 4, without Wi-Fi enabled and with the Home Screen displayed (not the Lock Screen), on the NFC label on top of the C460FW. The Galaxy Note 4 enables Wi-Fi, connects automatically to the C460FW directly and launches the Mobile Print app showing the options Print, Scan and Fax. It is also possible to launch the Mobile Print app first and then place the Galaxy Note 4 on the C460FW. In other words, the procedure is exactly the same as when wanting to print via NFC. If I select Scan, the Galaxy Note 4 displays buttons for previewing and scanning. Amongst other things, the app’s Settings menu allows you to select whether you want to save the scanned image as a JPEG, PNG or PDF file. The hiccups mentioned above when printing via NFC also apply to scanning. Nevertheless, scanning from the C460FW to the Samsung Galaxy Note 4 via NFC is still handy.

CONCLUSION

As I am mainly interested in printing text documents I have only tried to print a few colour photographs on plain copier paper, and they look good. Text in documents looks crisp. Despite the lack of automatic duplex printing the C460FW is an excellent peripheral, especially for the price, although I don’t pay for the consumables so I have no idea of the operating costs. The ease with which I got it printing and scanning in Gentoo Linux (laptop) and Android KitKat (Samsung Galaxy Note 4) means that I would definitely consider purchasing this model for home use.

Installing and using ZBar in Linux to scan bar codes with your Webcam

ZBar is an application that can scan and decode several bar code symbologies (including QR Code) from sources such as a Webcam or an image file. I had been wanting to install it for some time and was finally spurred on to do it by a request for help to get it working in the Sabayon Linux forums. Here are the steps I used.

1. I installed the package media-gfx/zbar-0.10-r1.
Note for Gentoo users: I merged the package with the imagemagick and v4l USE flags set, so that both zbarimg and zbarcam would be installed. If you only want to use ZBar with a Webcam then turn off the imagemagick flag and zbarimg will not be installed.
Note for Sabayon Linux users: The Entropy package was built with both the above-mentioned USE flags set, so zbarimg and zbarcam will be installed.

2. Then I checked the status of the installed package by using the Portage eix command:

$ eix -I zbar
[I] media-gfx/zbar
Available versions: (~)0.10-r1 {{X gtk imagemagick jpeg python qt4 static-libs +threads v4l xv}}
Installed versions: 0.10-r1(03:56:14 05/10/12)(X gtk imagemagick jpeg qt4 threads v4l xv -python -static-libs)
Homepage: http://zbar.sourceforge.net/
Description: Library and tools for reading barcodes from images or video

Sabayon Linux users could instead use the following command:

$ equo search --verbose zbar

3. Then I checked which video device my laptop’s inbuilt Webcam is:

$ ls /dev/video*
/dev/video0

4. As it is /dev/video0, I launched zbarcam as follows:

$ zbarcam --raw /dev/video0
WARNING: no compatible input to output format
...trying again with output disabled
ERROR: zbar processor in zbar_processor_init():
unsupported request: no compatible image format

Clearly zbarcam was not recognising the Webcam.

5. As I had installed the package with the Video4Linux USE flag set, I then launched zbarcam with the following prefix:

$ LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so zbarcam --raw /dev/video0

The ZBar GUI window popped up and I could see myself in the window. So far, so good.

6. I held a QR Code 2D bar code in front of the Webcam, then held a 1D Interleaved 2 of 5 bar code in front of the Webcam. The following was displayed:

$ LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so zbarcam --raw /dev/video0
http://roho.it/mryt
0161223563

Both the QR Code and the I2of5 bar code were read correctly. If the --raw parameter is omitted then zbarcam displays the symbology of the bar code too:

$ LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so zbarcam /dev/video0
QR-Code:http://roho.it/mryt
I2/5:0161223563

7. Then I tried using ZBar to read a bar code which I had previously saved as a .jpg file:

$ zbarimg --raw ~/zebra04.jpg
01234565
scanned 1 barcode symbols from 1 images in 0.04 seconds

$ zbarimg ~/zebra04.jpg
EAN-8:01234565
scanned 1 barcode symbols from 1 images in 0.04 seconds

To find out the other parameters available, use the commands:

$ man zbarcam
$ zbarcam --help
$ man zbarimg
$ zbarimg --help

ZBar is a nice tool. 😎