This article explains how to configure various operating system to use a serial console.
To get a login prompt on the serial port, you need to edit /etc/inittab. For example, if you have a vt100 connected to the first serial port at 128k baud, use a line such as the following:
T0:2:respawn:/sbin/getty -L ttyS0 115200 vt100
Note: we use Puppet to manage inittab. You must make this change in nodes.pp rather than editing inittab directly.
To make /dev/console the serial port, append "console=ttyS1,9600" to the kernel command line. You can replace 115200 by any valid baud rate. This will make calls to printk() display to the serial port.
You can have kernel messages displayed on both the serial port and the monitor by specifying two consoles, as in "console=ttyS0,115200 console=tty0".