cups fails with 'permissions' problem on serial printer

English Hardware
#1

I am trying to test GAINSCHA receipt printers on opensuse 11.4

They have supplied drivers and filter. I have added filter to /usr/lib/cups/filter and drivers(ppd files) to /usr/share/cups/model/gainscha/. I can add the printer model and driver from Yast.

The printer is a serial printer and I connect to it using ‘usb-to-serial’ converter. I can raw-print direct to printer by, ’ echo hello > /dev/ttyUSB0 '. It works.

Serial port parameters used while setting up Cups queue are correct. ( Tested via cutecom, opening port with the same parameters and writing to the port. It is also printing).

Now when I print from any application, the job is held up in Cups queue for reasons, ’ no permissions to port’. I tried becoming root and printing from kwrite. Again the same problem.

Any ideas? Thanks in advance.

#2

cups doesn’t run as root, it runs as user lp. Therefore your serial port must have rw permissions for user lp.

#3

I added user lp to dialout group, which has RW permissions on /dev/ttyUSB0, but to no avail. Then for testing, I added lp to group root, again to no avail.Then I ‘chmod’ ded permissions on /dev/ttyUSB0 to everybody. Then did cups work.

SuSEConfig should really have setup proper permission-scheme for serial printing when it setup the queue for me. But obviously it did not. I am not sure if this qualifies to be a bug, or it is an intentional design.

#4

It’s not something that users often do, connecting a serial port to cups. So sysadmin skills are still useful here. The best way to do it is with a udev rule. You can do something similar to what I did for a camera:

adding a new PTP camera to udev - Blogs - openSUSE Forums

Put it in a new rules file. You can also change permission and ownership as explained here: Writing udev rules