My OS is RHEL4.
there is no information about "serial port" in X11 system "HardWare exploer". Restart, in BIOS, serial port's IRQ and I/O Address are OK.
then I try "dmidecode", it shows as follows:

serial services are supported (int 14h)
Handle 0x0800
DM type 8,9 bytes
Port Connector Information
Internal Reference Designator: Not Specified // here different
Internal Connector Type: None
External Reference Designator: SERIAL
External Connector Type: DB-9 male
Port Type: Serial Port 16550A Compatible

I check the right machine, it displays:
Handle 0x0010
DMI type 8, 9 bytes.
Port Connector Information
Internal Reference Designator: COM1 Internal Connector Type: 9 Pin Dual Inline (pin 10 cut)
External Reference Designator:
External Connector Type: DB-9 male
Port Type: Serial Port 16450 Compatible

I donnot know how to specify my serial port to COM1!
waiting for your good suggestion.

COMx ports are Windows devices. You need to look in your /dev/ directory, for something along the lines of /dev/ttysx (where x is some number), such as /dev/ttys0 or /dev/ttyS0. The ttys0 would be your first serial port (equivalent to COM1), ttys1 would be COM2, etc.

If you're using a USB to serial converter, look for the /dev/ttyUSBx device, and use it.

the file /dev/ttys0 does exist, with a small red fork on the right top of its icon.

Then that's your first serial port. Configure minicom to use it.

Turn off hardware flow control if Minicom is showing as OFFLINE but you know its working! :-)

Uhh...this thread is from 2007. Very old and closed.

Three years, meh... Turns out that last reply was actually useful for me, at least.

:-) Thats why I did it!

Not that anyone will ever see this, but even old posts have value. This one helped me out.