[sane-devel] No scanners detected on LTSP fat client when net.conf uses hostname

[John Hupp]

I'm running Linux Terminal Server (LTSP), serving up the Lubuntu 14.04.2 
i386 desktop to fat clients.

I have an HP Scanjet 5200C scanner connected to the LTSP server and want 
the fat clients to be able to scan with that.

On the fat clients, the served image is actually running on the client 
hardware, making those systems similar in many ways to a group of 
standalone machines on the LAN.  So to get this running I have been 
following the simple tutorial at 
https://help.ubuntu.com/community/SaneDaemonTutorial

The last step is configuring /etc/sane.d/net.conf for sane clients, 
identifying saned hosts either by hostname or IP address.  I find that 
using the hostname works on another actual standalone machine on the 
LAN, but it fails with the fat clients.  So far I can only make fat 
client scanning work by entering an IP address.

But the server gets its IP address by DHCP, a feature I want to preserve 
so that I don't have to get into the router configuration when I set one 
of these up.  Needless to say, I really want to get this running stably 
for the fat clients using the hostname.

----------------------------

Troubleshooting: Trying to dig into this question, I find that the fat 
client can successfully ping the server hostname, so it's not a name 
resolution issue.

One interesting fact: Even on the server (where scanning always works), 
sane-find-scanner (even if run as root) reports "could not open USB 
device <id info>: Access denied (insufficient permissions)."  And on the 
fat client, sane-find-scanner reports the same even when net.conf 
identifies the saned host by IP address and Simple Scan successfully scans.

Is sane-find-scanner broken?

Some exercises with 'scanimage -L" (which I understand should be run as 
root):

On the server 'sudo scanimage -L' reports:
device hp:libusb:004:002 is a Hewlett Packard Scanjet 5200C flatbed scanner
device net:192.168.1.8:hp:libusb:004:002 is a Hewlett Packard Scanjet 
5200C flatbed scanner

If get to a root prompt on the fat client, then run 'scanimage -L' when 
net.conf is using an IP address, it reports:
device net:192.168.1.8:hp:libusb:004:002 is a Hewlett Packard Scanjet 
5200C flatbed scanner

Those devices presumably refer to /dev/bus/usb/004/002, which exists on 
the server.

If I run 'scanimage -L' on the fat client when net.conf is using a 
hostname, it reports no devices found.

While of some interest, I don't see that any of the above tells me much.

Any ideas?