Is it possible to do some echo on /dev/ttyS8 serial device in one terminal window, and in second to cat /dev/ttyS8 and display data from that file?


If you stick a serial loopback adapter in the specified serial port: Yes.

Serial Loopback Adapter
* Receive and transmit (2 & 3)
* Request to send and Clear to send (7 & 8)
* Data carrier detect, Data set ready and Data terminal ready (1, 6 & 4)

If you want to debug an application talking through a serial port, you could use this command:

socat /dev/ttyS0,raw,echo=0 SYSTEM:'tee input.txt | socat - "PTY,link=/tmp/ttyV0,raw,echo=0,waitslave" | tee output.txt'

(From https://unix.stackexchange.com/a/225904/127903)

  • So if I echo something to /dev/ttyS8 it goes out to UART port, and I cannot see it with cat, only with loopback adapter?
    – Junior
    Aug 27 '15 at 13:47
  • You need the loopback adapter. Serial transmit and receive pins are clearly defined. You can't get a response unless you receive your transmitted data via loopback adapter.
    – Jesse K
    Aug 27 '15 at 15:45

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