Arch Linux

Session

Member

Registered: 2008-06-23

Posts: 37

Permission to /dev/ttyUSB0

Hi, I am trying to get permission to /dev/ttyUSB0

ls -l /dev/tty* gives me

crw-rw---- 1 root uucp 188,  0 2009-12-03 17:25 /dev/ttyUSB0

groups session (my username) gives me

wheel network video audio optical storage users uucp mpd

I can't find the problem.

Login as root and there is no problem at all?

Session

Member

Registered: 2008-06-23

Posts: 37

Re: Permission to /dev/ttyUSB0

bump

DC

Member

From: Australia

Registered: 2009-12-23

Posts: 1

Re: Permission to /dev/ttyUSB0

I just had to work this out so that I could connect with my 3G modem (which uses /dev/ttyUSB0) without having to login as root (or sudo or su). I needed a udev rule.
First, I copied /lib/udev/rules.d/50-udev-default.rules to /etc/udev/rules.d/50-udev-default.rules since I didn't have a copy there to start with. According to the udev man pages, the rules in /lib are the system defaults, while the ones in the /etc subfolder are customised ones.

Then after the rule for serial devices I added a specific rule just for ttyUSB0 with relaxed permissions:

# serial
# this is the general rule that covers ttyUSB0 among others
KERNEL=="tty[A-Z]*[0-9]|pppox[0-9]*|ircomm[0-9]*|noz[0-9]*|rfcomm[0-9]*", GROUP="uucp"

# relax the permissions just for ttyUSB0
KERNEL=="ttyUSB0",              MODE="0666"

After that I just needed to unplug the modem and reconnect it, so that udev could recreate the device with the new permissions.

Doing this means I didn't have to add my normal user to the uucp group since I have read that doing so creates security issues. But then giving everyone rw access to ttyUSB0 probably creates security issues as well.

Hope that helps.
DC