Wifi scanner stopped working - Canon i-Sensys MF744Cdw

English Hardware
1

After one of the last few times I ran sudo zypper dup, sometime in the last week or two, my wifi scanner stopped working.

I noticed that the discovered name of the scanner changed from “eSCL Canon…” to “WSD Canon…”

I tried a few things, but so far to no success:

  1. turn off firewalld → oddly, the Document Scanner application seems to sometimes find it with the firewall on, but sometimes not. Nonetheless, if I then click on Scan, I get “Unable to connect to scanner”.
  2. roll back sane-airscan and avahi to their previous versions. No change. So I reran sudo zypper dup.
  3. sometimes scanimage says “[bjnp] add_scanner: Scanner MF742C/744C is not supported, model is unknown! Please report upstream”, but it also said “device ‘airscan:w0:Canon MF742C/744C (e1:…)’ is a WSD Canon MF742C/744C (e1:…) ip=192.168.x.x” or “device ‘airscan:w0:Canon MF742C/744C’ is a WSD Canon MF742C/744C ip=192.168.x.x”
  4. airscan-discover says “[devices] Canon MF742C/744C = http://192.168.x.x/active/msu/scan, WSD”
  5. sane-find-scanner yields no result

What could this be and what can I do?

2

It is possible that the device supports both driverless scanning protocols perhaps? If you have mdns allowed in the firewall, then discovery of scanners supporting eSCL will be possible.

What is returned by the following commands?

avahi-browse -rt _uscan._tcp

avahi-browse -rt _uscans._tcp

WSD uses a different protocol for discovery: WS-Discovery

Both scanimage -L and airscan-discover should report devices supporting either supported protocol.

Was /etc/sane.d/airscan.conf modified at all?

You can force or inhibit the discovery method if desired. Refer the config file or man sane-airscan for more info.

3

Thank you for your response!

It’s so frustrating. The scanner now works. All I did was put the computer in standby overnight, turn off the printer/scanner, and after turning everything back on again, I ran your first suggested command. Could the command have fixed this?

Here’s the result:

avahi-browse -rt _uscan._tcp
+ wlp6s0 IPv4 Canon MF742C/744C (e1:...) _uscan._tcp          local
= wlp6s0 IPv4 Canon MF742C/744C (e1:...) _uscan._tcp          local
   hostname = [Canond0799c.local]
   address = [192.168.x.x]
   port = [80]
   txt = ["usb_MFG=Canon" "mopria-certified-scan=1.2" "duplex=T" "is=platen,adf" "UUID=6d4..." "cs=color,grayscale" "pdl=application/octet-stream,application/pdf,image/jpeg" "representation=http://Canond0799c.local/en/media/dev_icon_128x128.png" "adminurl=http://Canond0799c.local:80/airprint.html" "rs=eSCL" "vers=2.63" "note=" "ty=Canon MF742C/744C" "txtvers=1"]

avahi-browse -rt _uscans._tcp yields no result.

I went into the web interface of the device and there’s indeed both Airprint (eSCL, right?) and WSD. Airprint is on, WSD Print is on, WSD Scan is off. How was it then discovered as WSD yesterday?

Would you recommend one protocol over the other?

I can see it was modified 3 days ago. Don’t know what changed though.

Well, my immediate problem is solved. But I don’t know why it appeared and how it solved itself. That’s a bit annoying and also cost me a fair bit of time yesterday. I would prefer for this not to happen again when I really need the device.

Any idea what could have happened here?

4

Sorry this was my mistake, I am the maintainer and forgot to actually tell that this file shouldn’t be replaced. Will do so, so this doesn’t happen again.

1 Like
5

So cool to hear from you!

Thanks for fixing it. Do you know what actually happened on my system?

6

an update overwrote the /etc/sane.d/airscan.conf file (where your scanner is being saved)

1 Like
7

Thanks for the explanation - I did wonder if airscan.conf had been modified.