I wrote Arduino sketch and it works. It waits for a command and answers text on response.

enter image description here

Simultaneously, I can't get any response with command line tools.

For example, I have the following code to get temperature:

exec 4<$tty 5>$tty
stty -F $tty cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts
#stty -F $tty 9600 -echo
#printf "temp\n" >&5
echo temp >&5
read reply <&4
echo "$reply"
#tail -n 1 - <&4

It returns empty or hang under different circumstances.

Also, if I run built-in Serial Monitor, I can see responses on command lines like:

echo temp > /dev/ttyUSB0

But I see nothing with commands like tail -f /dev/ttyUSB0

What I am doing wrong?

  • I really want to say using Linux is where you going wrong, but that would be childish. :) I'm not sure if I read it right, but are you trying to connect two apps to the same console port? I wouldn't expect that to work, but I only use Windows, does that work on Linux? Commented Oct 12, 2015 at 19:41

1 Answer 1


Add the flag -hupcl to your stty command. That will disable the assertion of DTR which is resetting the board.

 hupcl (-hupcl)
             Stop asserting modem control (do not stop asserting modem
             control) on last close.

The first time it is run there will be a reset, since setting that flag entails opening the port, which causes a reset. So you need to add a delay long enough to get past the bootloader - minimum 2 seconds, best make it 3.

You can do that with the sleep command: sleep 3

Note that you now won't be able to upload a new sketch since you have disabled the auto-reset feature that allows you to enter the bootloader, so before uploading a new sketch you need to turn the reset back on with

stty -F $tty hupcl

If you don't disable the reset then every operation in your script that opens and then closes the serial port will trigger a reset of the board. So in summary try this:

stty -F $tty cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts -hupcl
sleep 3
echo temp >$tty
read reply <$tty
echo "$reply"
stty -F $tty hupcl
  • I was wishing to use reset feature. Why doesn't it work with it?
    – Dims
    Commented Oct 12, 2015 at 19:44
  • In that case leave the stty as it is, but just add the three second delay so it can get past the bootloader before you send your request.
    – Majenko
    Commented Oct 12, 2015 at 19:45
  • I was waiting long enough with tail -f, also I was observing directly, that Serial Monitor does see the output, while tail -f does not.
    – Dims
    Commented Oct 12, 2015 at 19:45
  • You can't read the data with two things at once - only one thing will get it. Also you have to wait before sending "temp" otherwise it just won't ever get it.
    – Majenko
    Commented Oct 12, 2015 at 19:46
  • By the way, what are exact conditions for resetting? I have 3 commands in the script, touching the port: stty, echo and read. Will it reset 3 times or only one, how to know?
    – Dims
    Commented Oct 12, 2015 at 19:47

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