Serial port permissions -

Brian Mury brianmury at
Tue Oct 18 17:13:09 UTC 2011

>            [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

That looks good.

>        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.

Your test method is valid. You should see +12 volts or -12 volts (actually
anything between 3 and 15 meets the spec, but you'll usually see somewhere
around 12). Negative voltages are high, positive voltages are low, so if you
are seeing negative voltages, then those signals are asserted. The real
question is whether or not you see the signal *change* when toggling between
transmit and receive.

        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.

You shouldn't have to reboot, but it won't hurt anything.

Are you sure you are using the correct serial device (/dev/ttyS0, etc)? Do
you know it is otherwise working? Do you have some other serial peripheral
you can test it with - perhaps a TNC, or CAT control of your radio, for

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