Most embedded Linux / BSD systems such as routers, servers and nas devices comes with console interface (serial port with RS-232). BIOS can uses this, and after boot BIOS screen I/O is redirected so that you can use the device. RS-232 is also used for communicating to headless server, where no monitor or keyboard is installed, during boot when operating system is not running yet and therefore no network connection is possible. You need to use a serial cable between your computer and embedded system or server. In this post I will cover five conman utilities used for serial communication under Linux / Unix / *BSD and Mac OS X.