I would try to change the speed to 9600 from 115200 (also in putty).
If it does not work and you want to keep troubleshooting, I would reinstall IPFire using the normal procedure, then install minicom using packfire, finally using minicom, connect to putty and see if you can exchange text from both ends of the link. I can help if you want to try.
The point is to asses the correct functioning of the driver and the hardware in IPFire before doing anything else.
The thing is, after console=ttyUSB0 is applied, IPFire becomes unusable. It does not work, it does not navigate, as if it is not installed. The black message I posted, it is displayed via VGA/HDMI. Then everything freezes.
For the other things, I can try.
I think I always installed IPFire in the normal procedure. That is: I download the ISO, burn it and install the firewall without doing anything else. Correct?
Your profile indicates that you are plugging your Prolific pl2303âs USB plug to the mini-PC that is running IPFire. That is not the usual way to deploy such device. Typically, the RX & TX wires from the pl2303 device would go the the serial port on the IPFire mini-PC and the USB plug would go the desktop/laptop computer, from which you are controlling IPFire. The desktop/laptop would then find pl2303 as /dev/ttyUSB0. You will need to edit Putty (or other comms utility) to set the appropriate device.
IPFire uses a baud rate of 115200 with ARM devices. Itâs not documented what it uses with x86_64, but probably the same.
serial active by default states that serial is always active, on installed IPFire. You should not need to edit anything in IPFire, to set serial parameters.
Yes in fact I agree. The problem is that my mini-PC (IPFire) seems to lack a ânaturalâ serial port. Therefore, I cannot connect the RX and TX wires of the pl2303 device to the serial port of the mini-PC, because this port is nonexistent on my machine where IPFire is running. I believe this is the problem and conclude that it is probably impossible to use the serial console on an IPFire machine lacking a ânaturalâ serial port.
The other doubt I have is whether there is a priority between serial/vga-hdmi or the âconsole works simultaneously on serial and vga-hdmi.â
pl2303 devices are for low voltage serial interfaces, such as on Single Board Computers. Serial interfaces on x86_64 mainboards tend to use higher voltages and require a different cable/adaptor.
On ARM boards, âconsole works simultaneously on serial and vga-hdmi.â I donât have experience of serial on x86_64.
Serial interfaces can be troublesome and you donât need one when you have VGA.
You can set x86_64 systems up to have both vga/hdmi and serial interface control, I have done it in the past.
How can I do this? Assuming it is possible in my particular case.
You have to first have the standard rs232 type serial connector on your mini pc and it looks like you donât.
It would look like this
Trying to use a usb port as the equivalent of a normal com serial port is likely to be very complicated to do with a lot of hacking of the required code and I am not even sure if it is feasible or not. I certainly wouldnât be trying it if I had a vga/hdmi port on the system.
Why do you want to try running it with a serial port when you have the vga/hdmi connection?
If you really need to run it with a serial console connection then you need to look at purchasing a new system that has a serial com port.
After installing using the vga/hdmi, you can always remove the keyboard and display and do all your administration via an ssh terminal. Just make sure that the bios is not set to stop with an error during boot if there is a missing display or keyboard.
It would have been more practical. Since I only have one monitor, using serial would have saved me from connecting/disconnecting monitor+keyboard between the PC and the firewall. But nothing important. In the end, when IPFire works, it needs neither VGA nor serial, and I can still access it from Putty via IP address.
I agree with what you said. I have seen for myself that trying to use a usb port as the equivalent of a regular serial port is complex and probably not feasible.
@casabenedetti:
BTW, what kind of serial cable do you use?
There are 1:1 cables to connect an end device to a modem, and null-modem cables to connect two end devices. You need the null-modem type.
In short the two kinds of end to end connections are:
Yes, I tried both cables. That is: my USB serial is straight.
Straight doesnât go. I tried an adapter/cross cable grafted between the PC serial and the USB serial connected to the firewall. It still does not go.
I really think what @bonnietwin stated is correct 
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With machines that do not have VGA/hdmi and natural serial many times I was able to get it working. Outside of IPFire.
USB serial devices are for low voltage serial signals. You might have destroyed the serial side by connecting it to a conventional serial interface, that typically put out 12 V signals.
Your other alternative is a keyboard-video-monitor switch. I use a 4-way such on my IPFire box plus desktop PC.
You are right. I think the best thing is to resort to a data switch for monitor and keyboard. That way I solve all the problems in a simple way 
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