Serial console problems with stable/8

John Baldwin jhb at
Mon Sep 13 16:25:36 UTC 2010

On Monday, September 13, 2010 11:55:27 am Oliver Fromme wrote:
> John Baldwin wrote:
>  > On Monday, September 13, 2010 8:49:48 am Oliver Fromme wrote:
>  > > Now I get your point ...  Yes, -P does probe the keyboard
>  > > first.  That's probably why I see the boot0/boot2 on the
>  > > VGA console, not on the serial port.  As far as I know,
>  > > /boot.config is read by the boot0/boot2 stage, not by
>  > > loader(8).
>  > 
>  > But loader inherits the settings from boot2, so if you set it in
>  > /boot.config you do not need to set anything in loader.conf.  Also,
>  > having boot2 use serial is good in that you can boot loader.old if
>  > you ever get a broken /boot/loader.  Using '-Dh' in /boot.config is
>  > what I do on all the boxes where I use a serial console.
> Makes sense.  I'll change -P to -Dh.
> But having console="comconsole" in loader.conf should also
> enable the serial console, except that it happens a little
> later (in loader instead of boot2), right?


> I think the boot.config stuff might be a red herring.
> The console breaks (i.e. freezes) as soon as I try to run
> a getty process on it -- That seems to indicate that getty
> does *something* to the console device which causes the
> problem.  The wchan "ttydcd" seems to indicate is has
> something to do with carrier detection or flow control.
> This points to the uart driver as the culprit which
> replaced sio.

Well, /dev/ttyXX have always waited for carrier detect, whereas /dev/cuaXX 
(the call-out devices) have not.  That was so that you could hook a modem up 
to a serial port and getty would not return from open(2) and print a login 
banner until someone dialed the modem and connected.  I think Jeremy has 
already given you some good things to try (such as 3wire.9600) to debug this 

>  > > Anyway, I don't care too much for boot0/boot2; I've never
>  > > had to interact with them on that machine.  The important
>  > > thing for me is that loader(8) and the kernel use the
>  > > serial port for the console, and that I can login on it
>  > > (i.e. there must be a getty running).  All of that seemed
>  > > to be accomplished with the console="comconsole" entry in
>  > > /boot/loader.conf ...  At least it worked when I first
>  > > installed that machine in September 2000 (yeah, exactly 10
>  > > years ago) with FreeBSD 4.1, then updated it roughly every
>  > > two years ...  And it stopped working in 8.x.
>  > 
>  > Did you update your hints to rename the 'sio' hints to 'uart'?
> Yes, mergemaster did that for me.  I double-checked it.
> hint.uart.0.port="0x3F8"
> hint.uart.0.flags="0x10"
> hint.uart.0.irq="4"

Ok.  I know that for machines I have at work that run 7, if I boot a 8.x
kernel have to explicitly unset the sio hints and set the uart hints for
the serial console to work in 8.

John Baldwin

More information about the freebsd-stable mailing list