auto permissions on udev'd device files?

Question

This is a dupe from SuperUser.com . Folks over there weren't smart enough or willing to help me out; maybe it's more a programmer question than an administrator one:

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I have an app that reads input from 4 (four) mice that are plugged in via USB in addition to the built-in touchpad. This is no problem for Ubuntu 9.10: hald notices the new devices and udev's them brand new entries called /dev/input/mouse4 ... mouse7.

My app runs as a normal user app. The files in /dev belong to root and aren't readable to anyone else.

I don't have a problem doing chmod a+r mouse? once, but the devices come and go with every reboot and every time the dang rodents are plugged in or out.

Can someone please tell me a script or something to manipulate so my chmod happens automagically?

Answer 1

This information is easily discoverable, I just had to look at /etc/udev/rules.d/91-permissions.rules on a Debian configuration. :-)

Some interesting examples pasted from there:

# default permissions for block devices
SUBSYSTEM=="block",                             GROUP="disk"

Looks like there's this "GROUP" thing to determine the group owner...

And, you can chmod stuff apparently:

KERNEL=="pty*",                 MODE="0666",    GROUP="tty"

Note the MODE part...

I'm sure RTFM-ing for the udev config file format will give you even more information. :-)