The missing link turns out to be assigning a device node with the proper owner, group, and permissions to let saned share the scanner over the network. IIRC, this worked right out of the box in previous versions of Xubuntu, but now requires manual tweakage.

That post gives the steps for my old SCSI scanner. It turns out that the udev rule is not optional for USB scanners… at least not in 12.04, anyway.

In order to build the udev rule, you start with lsusb:

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 008 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 002: ID 0424:2504 Standard Microsystems Corp. USB 2.0 Hub
Bus 002 Device 005: ID 0d8c:000c C-Media Electronics, Inc. Audio Adapter
Bus 002 Device 006: ID 046d:c52f Logitech, Inc. Wireless Mouse M305
Bus 008 Device 006: ID 04a9:220e Canon, Inc. CanoScan N1240U/LiDE 30
Bus 008 Device 003: ID 413c:1003 Dell Computer Corp. Keyboard Hub
Bus 008 Device 004: ID 413c:2010 Dell Computer Corp. Keyboard

That gives you the bus and device numbers, which means the corresponding device is, at least right now:

/dev/bus/usb/008/006

The udevinfo command I used a while ago has Gone Away, replaced by udevadm with even more syntactic sugar:

udevadm info --query=all --attribute-walk --name=/dev/bus/usb/008/006

Which produces a ton of information, starting with:

  looking at device '/devices/pci0000:00/0000:00:1d.2/usb8/8-1':
    KERNEL=="8-1"
    SUBSYSTEM=="usb"
    DRIVER=="usb"
    ATTR{configuration}==""
    ATTR{bNumInterfaces}==" 1"
    ATTR{bConfigurationValue}=="1"
    ATTR{bmAttributes}=="a0"
    ATTR{bMaxPower}=="500mA"
    ATTR{urbnum}=="18658"
    ATTR{idVendor}=="04a9"
    ATTR{idProduct}=="220e"
    ATTR{bcdDevice}=="0100"
    ATTR{bDeviceClass}=="ff"
    ATTR{bDeviceSubClass}=="00"
    ATTR{bDeviceProtocol}=="ff"
    ATTR{bNumConfigurations}=="1"
    ATTR{bMaxPacketSize0}=="8"
    ATTR{speed}=="12"
    ATTR{busnum}=="8"
    ATTR{devnum}=="6"
    ATTR{devpath}=="1"
    ATTR{version}==" 1.10"
    ATTR{maxchild}=="0"
    ATTR{quirks}=="0x0"
    ATTR{avoid_reset_quirk}=="0"
    ATTR{authorized}=="1"
    ATTR{manufacturer}=="Canon"
    ATTR{product}=="CanoScan"

Extracting the two highlighted values lets you create a udev rule. If your udev-fu is strong, you can pluck them directly from the lsusb output.

I created a new file:
/etc/udev/rules.d/60-scanner.rules

Which contains this rule:

# Canon LiDE 30 scanner
ATTRS{idVendor}=="04a9",ATTRS{idProduct}=="220e",SYMLINK+="scanner",MODE="0660",OWNER="root",GROUP="saned"

Based on the advice there, I added the port number to the /etc/xinetd.d/saned stanza, but I’m not sure it’s needed:

service sane-port
            {
              port = 6566
              socket_type = stream
              server = /usr/sbin/saned
              protocol = tcp
              user = saned
              group = scanner
              wait = no
              disable = no
            }

After doing all the rest of the saned and xinetd setup, unplug and replug the scanner, which should produce these devices:

ll /dev/bus/usb/008/006 /dev/scan*
crw-rw----+ 1 root saned 189, 901 Jan  5 21:30 /dev/bus/usb/008/006
lrwxrwxrwx  1 root root        15 Jan  5 21:14 /dev/scanner -> bus/usb/008/006

And then it should Just Work…