First, find the serial ports:
ferdy@TestServer:~$ dmesg | grep tty
[0.000000] console [tty0] enabled
... ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
... ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A
Use the screen command to connect to a serial port:
screen – screen manager with VT100/ANSI terminal emulation
Example, connecting using serial port ttyS0 and 9600 baud rate
$ sudo screen /dev/ttyS0 9600
Use CTRL-A to detach
Use screen -R to reattach or screen -r <session>