[KLUG Members] Brother printer inconsistency

[Daniel Hedlund]

Peter Bart wrote:
>     I think I have a similar problem with a Brother DCP7020. I use a
> laptop with a port replicator into which my printers usb cord is plugged
> in. So I disconnect and reconnect the usb cord every day, sometimes
> several times in a day. I went into cups and there I have two printers,
> with the default destination being "Device URI: usb:/dev/usb/lp0". I
> think I'm missing something about the part where you attach the printer
> settings directly to '/dev/usb/lp0'. Both in cups and yast the correct
> one is listed as the default. I don't think that's what you're talking
> about though. Could you please expand on your statements for a newbie?
> Peter

Your printer port settings seem fine to me, so your problem must be 
related to something else.  With issues were related to using a 
Fedora-based system which uses a HAL (hardware abstraction layer) to 
uniquely identify each printer.  The idea with the HAL layer is that if 
I was to have two printers plugged in at the same time, Linux would be 
smart enough to know which of the two printers I was referring to when I 
chose the "Brother HL-1440" printer to print to, instead of for example 
sending it to a HP InkJet.  If you were to have two printer connected to 
two different USB devices, using /dev/usb/lp0 and /dev/usb/lp1, it just 
wouldn't work properly; the first printer that was plugged in at any 
given time would be allocated lp0, regardless of whether the drivers 
matched up or not.

Your cups settings seem okay in that if you have only one printer 
attached, /dev/usb/lp0 is always chosen and your problem shouldn't be 
with port naming.  My problem was a printer attached to a print server 
running on a dodgy laptop with a broken screen and a dodgy network card. 
  I would often have to restart the computer to get networking support 
again and sometimes didn't have the time so I would disconnect the 
printer from the USB and attach it directly to the computer I wanted to 
print from.  When I'd reattach the printer or restart the computer, 
there was sometimes a chance that it would attach with a different HAL 
device name and cause me headaches.

Your problem with your printer is probably related to the printer going 
offline according to cups and not reinitializing its status to cups as 
being online again.  If you were to go into the cups interface 
(http://localhost:631/), you might find that your printer says its 
status is "offline" for example.  Normally you would have to click on 
"Start Printer" and everything would continue where it left off?  If 
that's the case then it's just a problem with your USB printer updating 
the cups status.  My USB printer(s) used to not update their CUPS status 
when plugged in, but after upgrading my distro a version or two, it has 
since started updating automatically.  I think the updates are working 
because of the D-BUS and/or possibly HAL related interfaces in my 
distribution (maybe CUPS is now HAL aware).  Either CUPS is polling the 
USB port occasionally now or there is some hook somewhere that finally 
telling CUPS to change its status.  I haven't looked into this in any 
detail.  Each Linux distro is different at the moment in how it's 
handling system events and/or messages.  Some distros are still using 
udev, some hotplug, some HAL.  It's a big mess at the moment and will 
eventually become standardized and consistent across distros.  Until 
that point, it's very difficult for applications to properly hook things 
together at the system level.

Cheers,

Daniel Hedlund
daniel at digitree.org