How to find serial port

My dell dimension 8400 has a serial port on the back. I want to use minicom to interface the serial port on this computer with Ubuntu installed.

The output of dmesg | grep tty did not give me much useful information however. I could not find anything with the key word "Serial":

[    0.000000] console [tty0] enabled
[    0.778096] 00:05: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
[    0.867939] 0000:04:01.0: ttyS5 at I/O 0xcc08 (irq = 17, base_baud = 115200) is a 16450
[    0.868098] 0000:04:01.0: ttyS6 at I/O 0xcc10 (irq = 17, base_baud = 115200) is a 8250
[    0.868246] 0000:04:01.0: ttyS7 at I/O 0xcc18 (irq = 17, base_baud = 115200) is a 16450
[    0.868394] 0000:04:01.0: ttyS8 at I/O 0xcc20 (irq = 17, base_baud = 115200) is a 8250
[    0.868542] 0000:04:01.0: ttyS9 at I/O 0xcc28 (irq = 17, base_baud = 115200) is a 8250
[    1.134731] tty tty36: hash matches

How can I find the serial port, so I can interface my old Terminal Node Controller with minicom? I remember the serial port working just fine on CentOS with the same system.

The output from dmesg is not the result you want you still have to run the command:

setserial -g /dev/ttyS[0123456789]

The output would be like:

/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: 16550A, Port: 0x1020, IRQ: 18
/dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4
/dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3
....
/dev/ttyS7, UART: unknown, Port: 0x1020, IRQ: 18
/dev/ttyS8, UART: unknown, Port: 0x03e8, IRQ: 4
/dev/ttyS9, UART: unknown, Port: 0x02e8, IRQ: 3

So as shown above The unkwon UART is not taken so you can use ttyS0 ot ttyS1.

Try this for your system and check.

More if you still use some old Ubuntu version < 14.04 you can use gtkterm which is a simple GTK+ terminal used to communicate with the serial port.

sudo apt-get install gtkterm