If you were to boot into the floppies that you just made, FreeBSD would boot into its normal install mode. We want FreeBSD to boot into a serial console for our install. To do this, you have to mount the boot.flp floppy onto your FreeBSD system using the mount(8) command.

# mount /dev/fd0 /mnt

Now that you have the floppy mounted, you must change into the /mnt directory:

# cd /mnt

Here is where you must set the floppy to boot into a serial console. You have to make a file called boot.config containing /boot/loader -h. All this does is pass a flag to the bootloader to boot into a serial console.

# echo "/boot/loader -h" > boot.config

Now that you have your floppy configured correctly, you must unmount the floppy using the umount(8) command:

# cd /
# umount /mnt

Now you can remove the floppy from the floppy drive.

You now need to connect a null-modem cable between the two machines. Just connect the cable to the serial ports of the 2 machines. A normal serial cable will not work here, you need a null-modem cable because it has some of the wires inside crossed over.

It is now time to go ahead and start the install. Put the boot.flp floppy in the floppy drive of the machine you are doing the headless install on, and power on the machine.

Now you have to connect to that machine with cu(1):

# cu -l /dev/cuad0