[sane-devel] scanbd occasionally ignores scanner button presses

Milan Knížek knizek.confy at gmail.com
Fri May 16 07:38:16 UTC 2014

Hello devs!

I have setup scanbd to poll CanoScan 9000F button presses (Arch Linux,
x86_64, sane-git from 2013-07-08, scanbd 1.3.1), scanbd.service and
scanbm.socket are run through systemd unit files.

It usually works just fine, but randomly scanbd completely ignores the
button presses - usually, it does not even help to switch the scanner
off/on. The only reliable solution so far is to restart the

I increased the debug level to 3 and watched syslog for messages when
scanbd operates normally and when it ignores the presses. I could not
find anything unusual in the messages. Scanbd continues to send lot of
repeated messages (like in normal state), but pressing a button does not
log any messages anymore.

I have yet to confirm it by further testing, but it seems that I can
trigger the "stale" status of the scanbd by repeatedly pressing the
scanner button (e.g. the PDF merge button, which does not really scan
anything) in a quick sequence.

Is this a known behaviour? How can I debug it further?

Is there any SIGNAL I could send to scanbd process to refresh itself
without the need to restart scanbd.service?

At the moment, I implemented a workaround by killing (SIGKILL) the
scanbd process every time the button is pressed and restarting
scanbd.service (at the end of the action script).


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