To get full access to your Linux Server via a serial connection you need a few little tweaks. You have to tell grub to use the serial console and to display a simple chooser. You also have to tell the kernel to print its output to the serial port as well.
enable serial console
The tweaks are done in /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,9600n8" GRUB_TERMINAL=console GRUB_SERIAL_COMMAND="serial --speed=9600 --unit=0 --word=8 --parity=no --stop=1"
You will also need a login shell on the serial port.
Therefore you have to uncoment the following line in /etc/inittab
T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100
At the next reboot you will be able to connect your Linux Server via a serial connection using your favorite terminal application at 9600 8n1.