7.4. Serial console is not /dev/modem
In many Linux distributions the file /dev/modem is a symbolic link to the
serial port containing a modem which is available for use.
Although the serial console is a serial port with a modem, we
certainly don't want it used to place an outgoing call.
Check that /dev/modem
does not point to the serial port being used for the console, say
/dev/ttyS0. If it does,
then remove the symbolic link.