Serial port permissions -

Bob Goodwin bobgoodwin at wildblue.net
Tue Oct 18 16:42:59 UTC 2011


On 18/10/11 12:21, Bob Goodwin wrote:
> On 18/10/11 12:00, Brian Mury wrote:
>> On Tue, 2011-10-18 at 11:36 -0400, Bob Goodwin wrote:
>>>              How do I determine if I have the right serial port
>>>              permissions, where do I look?
>> The serial port device should be owned by root, and belong to the
>> dialout group, with both the owner and the group having read and write
>> permissions. You can verify this like this:
>>
>>> ll /dev/ttyS*
>> crw-rw---- 1 root dialout 4, 64 Oct 18 01:21 /dev/ttyS0
>> crw-rw---- 1 root dialout 4, 65 Oct 18 00:28 /dev/ttyS1
>> crw-rw---- 1 root dialout 4, 66 Oct 18 00:28 /dev/ttyS2
>> crw-rw---- 1 root dialout 4, 67 Oct 18 00:28 /dev/ttyS3
>> crw-rw---- 1 root dialout 4, 68 Oct 18 01:14 /dev/ttyS4
>> crw-rw---- 1 root dialout 4, 69 Oct 18 00:29 /dev/ttyS5
>> crw-rw---- 1 root dialout 4, 70 Oct 18 01:28 /dev/ttyS6
>> crw-rw---- 1 root dialout 4, 71 Oct 18 01:10 /dev/ttyS7
>>
>> Yeah, I've got a lot of serial ports! :-)
>> The column that says "root" is the owner.
>> The column that says "dialout" is the group.
>> The second and third characters are the owner read/write permissions (r
>> or w indicates permission, - indicates no permission).
>> The fifth and sixth characters are the group read/write permissions.
>>
>> You can run "system-config-users" as root, and add your user account to
>> the dialout group. You'll need to log that user out and back in after
>> making that change.
>>
>> Brian
>>
>>
>
>        This is what I see there and it looks ok to me:
>
>            [bobg at box9 ~]$ ll -al /dev/ttyS*
>            crw-rw----. 1 root dialout 4, 64 Oct 18 03:14 /dev/ttyS0
>            crw-rw----. 1 root dialout 4, 65 Oct 18 03:14 /dev/ttyS1
>            crw-rw----. 1 root dialout 4, 66 Oct 18 03:14 /dev/ttyS2
>            crw-rw----. 1 root dialout 4, 67 Oct 18 03:14 /dev/ttyS3
>
>        I haven't changed anything in "system-config-users" I've set up
>        on a second F-15 computer and still can't see anything toggle on
>        DTR or RTS. Perhaps my test method is invalid? I am simply
>        looking at the voltage between signal ground and those two
>        points at the end of a cable with no termination, it is always a
>        high negative value, above 12 volts.
>
>        Bob
>
>

        Ok I've added "dialout" but still don't see a change in voltage,
        on the second computer it sits at -11+? I logged out/in, perhaps
        a reboot is required?  I'll try that.

        Bob





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