View Full Version : [ubuntu] Possible problem with /dev/*lp* in new installations

March 24th, 2010, 12:24 AM
I recently installed Ubuntu 9.10 and have been trying to set up a USB printer.

I hit a problem which I eventually diagnosed as being the ownership of /dev/usb/lp0.

First, the symptom:

~$ cat Test > /dev/usb/lp0
bash: /dev/usb/lp0: Permission denied

The initial diagnosis:

~$ ls -l /dev/usb/lp0
crw-rw---- 1 root lp 180, 0 2010-03-23 21:39 /dev/usb/lp0

Notice the lp group? When I checked group properties, this group did not have any members - not even root!!!

The default for CUPS (from the CUPS doc) is lpadmin, in any case, so not sure what lp is all about. In fact, the 'lp' group has ID=0, the same as the 'root' group.

I fixed it by doing this:

~$ sudo chown root:lpadmin /dev/usb/lp0

Then I noticed that /dev/lp0 and /dev/parport0 also had group=lp, so I also did this:

~$ sudo chown root:lpadmin /dev/lp*
~$ sudo chown root:lpadmin /dev/parport*

Am I correct that this is an installation issue, or have I misdiagnosed?

March 24th, 2010, 11:57 AM
I can add some more info to this thread. This issue is totally irrelevant as far as CUPS is concerned - please ignore the references to CUPS. I can now print through CUPS despite not being able to do something like

echo Test > /dev/usblp0

(CUPS works when the URI is parallel:/dev/usblp0, rather than usb:/dev/usblp0)

However, I'm curious as to why this simple redirection to the device is disallowed until I change the permissions.