Binary package hint: apparmor
Context:
I'm trying to get cups to print to an old label printer connected to my laptop through an usb-to-RS232 cable. Ubuntu 10.10.
Bug:
AppArmor prevents cups to access /dev/ttyUSB0. CUPS returned a "permission denied error". I expect that CUPS sends the data to the printer.
dmesg show:
type=1400 audit(1290167643.039:240): apparmor="DENIED" operation="open" parent=4772 profile="/usr/sbin/cupsd" name="/dev/ttyUSB0" pid=4802 comm="serial" requested_mask="rw" denied_mask="rw" fsuid=0 ouid=0
After issuing sudo aa-complain /usr/sbin/cupsd printer receives data (light flashes). It doesn't work but it's likely an unrelated problem. CUPS stops complaining.
Likely cause:
I don't understand AppArmor, but in /etc/apparmor.d/usr.bin.cupsd I find this lines:
deny /dev/tty*
/dev/ttyS*
If I understood it correctly (if I do kudos to AppArmor developers), we need to add another exception for this kind of adapter, something like
/dev/ttyU*
ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: apparmor 2.5.1-0ubuntu0.10.10.2
ProcVersionSignature: Ubuntu 2.6.35-23.40-generic 2.6.35.7
Uname: Linux 2.6.35-23-generic i686
Architecture: i386
Date: Fri Nov 19 13:03:51 2010
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Beta i386 (20100901.1)
ProcEnviron:
LANG=gl_ES.utf8
SHELL=/bin/bash
ProcKernelCmdline: BOOT_IMAGE=/boot/vmlinuz-2.6.35-23-generic root=UUID=d8a4ecb5-65d3-4bc5-8867-4a88c10451c5 ro quiet splash
SourcePackage: apparmor
Note that in the end of attached KernLog and ApparmorStatus I had manually put AppArmor in audit mode.