What is the proper way to listen on serial port using minicom?

Question

I have found tutorials about using minicom to communicate with modems, but none about just listening what data arrives to the serial port of my desktop computer.

I will ask for this case scenario:

• Utilite Pro computer (embedded device like RaspBerry that includes two serial ports).
• Ubuntu Linux v14.04 on desktop computer. Serial port on /dev/ttyS0.
• Minicom on desktop computer (Linux) already configured for 115.200 bps, 8 data bits, 1 stop bit, no flow control. This is the configuration of the Utilite device for its COM port.
• Serial cable, of course, connected between the Utilite computer and the desktop computer. This serial cable is included in the original box of the device (I don't know if it is null-modem, but I presume it should be the appropriate one).

It is supposed that the Utilite Pro starts outputing diagnose data to its COM port at the moment it starts running.

How can I read this data using minicom?

Both data on screen and to file methods if possible, please.

ADDITIONAL DATA:

• The Utilite operating system is not relevant here, as long as it is its bootloader (U-Boot) who sends the data to serial port. Even if the Utilite does not boot, the data will be sent to COM port.

Answer 1

By default minicom listens for serial data on /dev/modem, this is typically a symlink to the first serial TTY. Sometimes the first serial TTY is not the hardware DB9 port. So the first thing you need to know is which serial TTY your Utilite device is connected to. The easiest way to do that would be run:

for $dev in $(ls /dev/ttyS*); do
  temp=$(mktemp)
  echo $temp
  echo $dev >$temp
  cat $dev >>$temp &
done

Then boot your Utilite device. This will dump the stream from the TTY port to one of the temp files listed in that scripts output. Check each temp file to determine which port you need to configure minicom to use. You can then start minicom with the "-D" option followed by the device. Provided the speed and flow control settings are appropriate, as you say, you should then see the output from your device stream in minicom.