permissions denied on serial port /dev/ttyACM0

Serial port is very commonly used when developing embedded systems such as Arduino or Particle core.

But we might encounter the following problem when trying to open the serial monitor:

                   Permission denied, cannot open /dev/ttyACM0

Many suggest to do:

              sudo chmod 666 /dev/ttyACM0

I don't know them but it did NOT work for me. This DID:

sudo usermod -a -G dialout boris

in which boris is my username.
And call:

      groups boris

to check.

Maybe you gotta login again.


Ref:
http://askubuntu.com/questions/616517/dev-ttyacm0-permission-denied-error
http://askubuntu.com/questions/58119/changing-permissions-on-serial-port