Date: Fri, 22 May 2026 17:13:36 -0700 From: Steve Rikli <sr@genyosha.net> To: Polarian <polarian@polarian.dev> Cc: questions@freebsd.org Subject: Re: Terminal server with consumer hardware Message-ID: <ahDxMJvzBdwf26ts@dragon.home.genyosha.net> In-Reply-To: <20260522231322.3a0dbd36@Hydrogen> References: <20260521233422.001d364f@Hydrogen> <ca6a4d16-9918-4f8d-a198-4f09ff8bba46@dorfdsl.de> <20260522154731.4cad8798@Hydrogen> <ahCMovnPJ6qjU9Nx@dragon.home.genyosha.net> <20260522231322.3a0dbd36@Hydrogen>
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On Fri, May 22, 2026 at 11:13:22PM +0100, Polarian wrote:
>
> > It's been quite a while since I looked at this, but AFAIK FreeBSD
> > can't make use of USB serial devices for the system console.
>
> The man pages cause some confusion here then, as freebsd.efi(8)
> explicitly state that if you do not have support for it within your
> uefi bios, maybe this is just me getting confused.
I assume you mean loader.efi(8).
While it doesn't specifically say "COM ports only", IMO it essentially
implies that in this table:
Windows Name I/O Port Address Typical FreeBSD device
COM1 0x3f8 /dev/uart0
COM2 0x2f8 /dev/uart1
COM3 0x3e8 /dev/uart2
COM4 0x2e8 /dev/uart3
I dunno if that's the final word though, and it's quite possible things
have changed since I last looked. There might be some hope from settings
like comconsole_pcidev as described in loader_simp(8) but I haven't
tried anything with it.
> > I.e. there must be an actual serial port, recognized by the bios and
> > presented to the OS. Something like this, if found:
> >
> > $ dmesg | grep ^uart[0-9]:
> > uart0: <16550 or compatible> port 0x3f8-0x3ff irq 4 flags 0x10 on
> > acpi0 uart0: console (115200,n,8,1)
>
> Ah so it must be presented by acpi, in which case this requires
> firmware support within the motherboard full stop.
With modern hardware it's typically acpi, yes. But I don't think it
necessarily must be; e.g. in older releases and hardware, there were
other default settings in /boot/device.hints for the uarts, something
like:
hint.uart.0.at="isa"
I don't recall when the default changed to "acpi", I think it's been
a while. device.hints(5) talks about format and syntax.
Afaik for console purposes the serial device must have a uart(4),
regardless of origin.
> The man page still doesn't make sense on this though. I wonder who
> would be a good person to ask about it, because if it isn't possible
> then surely the man page needs improvements for being misleading or not
> clear enough for idiots like me :p
I'm no expert at all, a while ago I simply spent a lot time websearching,
reading man pages, and experimenting with an old NUC.
Ultimately I "solved" the situation here by primarily using systems
with a native (built-in) serial port. :-)
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