/dev/ttyS0 permission error

Jay Cliburn jacliburn at bellsouth.net
Sun Dec 3 03:23:12 UTC 2006


I've seen references to this scattered about on the web, but no solutions.

I installed FC6 on a Dell Inspiron 4000 laptop to use as a serial console for 
debugging kernel problems.  Whenever I start minicom on the laptop, however, I'm 
greeted with a permission denied error to /dev/ttyS0.  Sure enough, the perms on 
ttyS0 are 0660 and I'm not a member of the uucp group:

crw-rw---- 1 root uucp 4, 64 Dec  1 06:04 /dev/ttyS0
crw-rw---- 1 root uucp 4, 65 Dec  1 06:03 /dev/ttyS1
crw-rw---- 1 root uucp 4, 66 Dec  1 06:03 /dev/ttyS2
crw-rw---- 1 root uucp 4, 67 Dec  1 06:03 /dev/ttyS3

No problem, I thought -- I'll just gin up a udev rule and set the perms to 0666. 
  Sorry; doesn't work.  As a matter of fact, it gets worse: perms on ttyS0 go to 
0600 root:root as a result of my new local rule.

Okay, not an ideal solution, but let's modify 50-udev.rules and set the default 
rule for tty[A-Z]* to MODE="0666".  Nope.  Now they're *all* 0600 root:root.

Here's the rule:
KERNEL=="ttyS0", NAME="%k", GROUP="uucp", MODE="0666"

I had no problems with this under Debian Etch and Knoppix Live running on the 
same laptop.  Debian was running a 2.6.17 kernel, and for the life of me I can't 
remember the Knoppix kernel version (the web site says 2.6.x -- big help), and I 
don't have the CD here at home.

The current workaround is to add non-root users to the uucp group.  (Or maybe 
this is the solution?)  Any ideas why I can't get a udev rule to change the 
perms to 0666 on /dev/ttyS0?

Thanks,
Jay





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