Re: Can't seem to get serial to work

i always thought you needed to be in the dialer group to open com ports.


On 7/13/2026 3:35 AM, Frank Leonhardt wrote:
> On 03/07/2026 14:28, Polarian wrote:
>> After inspecting the motherboard, I found a JCOM header, this allows me
>> to connect serial. So I connected a startech plate adapter to it [1]
>> and then plugged in a nullmodem to it [2] and then connected a through
>> cable to that.
>>
>> Server side I see the dmesg log for COM0 [3], and the interfaces. [4]
>>
>> However whenever I plug the DB9 to USB through cable into any device,
>> there is no interface which is created, and dmesg shows nothing. I am
>> honestly clueless of what more I can try.
>
> As this has been around for a while...
>
> I don't know exactly what you're doing here, but connecting a terminal 
> to a serial interface doesn't create a device. If the UART (real or 
> emulated) is detected, that's as good as you'll get.
>
> You might be hitting hardware flow control problem. However, I can't 
> figure for certain what the "DB9 to USB through cable" is about. I'm 
> guessing that on host A you have some kind of serial port breakout 
> which you believe is COM0. You have connected this to a DB9 IBM-PC 
> style connector using a Startech passive adapter. Into this you have a 
> null modem cable connected to a Serial USB adapter on another host.
>
> Does the other hose enumerate the USB->Serial adapter?
>
> Try looping back pins 2+3 on both hosts and see if you get your data 
> echoed back on each.
>
> Look in /dev for devices /dev/cua*
>
> Note that I think USB serial devices use a capital U; native UARTs 
> uses a lower case u.
>
> Let's say you find cuau0
>
> Force hardware flow control OFF:
>
> stty -f /dev/cuau0 -crtscts
>
> Connect to it using cu:
>
> cu -l /dev/cuau0 -s 9600
>
> Type something and see if it echos back. (Use ~. on a blank line to exit)
>
> If you don't have a cuau device in /dev/ that's your first problem. If 
> you don't have echo back then your UART is the problem. If you have 
> echo back on both then your cross-over cable is the problem. You may 
> need to loop back the hardware handshaking lines - disabling them in 
> software is obviously not the answer if they're enabled at power-on.
>
> If you're not getting your USB->Serial converter appearing as 
> /dev/cuaU[0-9] run usbconfig and see what it finds.
>
> Regards, Frank.
>
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