cu -l /dev/nmdm not setting rows and columns

John-Mark Gurney jmg at
Wed Nov 26 23:44:33 UTC 2014

Craig Rodrigues wrote this message on Wed, Nov 26, 2014 at 15:34 -0800:
> On Sun, Nov 23, 2014 at 6:04 PM, Peter Grehan <grehan at> wrote:
> > Hi Craig,
> >
> >  # stty -a
> >> speed 9600 baud; 0 rows; 0 columns;
> >> # echo $TERM
> >> dialup
> >>
> >> Any idea how I can fix this?  The console inside the VM
> >> is quite unusable when it does not have the correct
> >> rows/colums set.
> >>
> >
> >  Not sure how you're getting 'dialup' as the terminal type: the default
> > ttys file for 10.1 shouldn't need to be edited, and has
> >
> > ttyu0   "/usr/libexec/getty std.9600"   vt100   onifconsole secure
> >
> >  The rows/columns is always 0 for uart-style serial lines since it's not
> > possible to know what's on the other end. That's why $TERM has to be set
> > correctly for these.
> >
> >  Having an xterm attached to the other end of an nmdm device isn't too
> > different from swapping say a vt100 with a vt420 or some other terminal
> > with a different resolution on a real serial line. There's no way for the
> > serial driver to know this has happened.
> >
> >  The only way to fix the changing-size problem is to have a
> > paravirtualized tty device that has a way of reading the terminal window
> > size and being informed of changes. The virtio-serial specification has
> > this ability, however, the FreeBSD driver for this can't operate in polled
> > mode so can't be the main console port, and in any event there's no bhyve
> > backend for it currently.
> >
> >  Or, you can network-login to the guest in which case xterm works fine :)
> I need to log into the serial console for two reasons:
>    -> networking has not been set up yet, and I need to log in to see what
> is going on
>    -> networking has failed or been misconfigured, so I cannot ssh into the
> VM, but I still need to log in to see what is going on
> cu and tip are in the base system, so they are handy to use, but they are
> quite primitive.
> Do programs like minicom work better for this type of thing, in terms of
> presenting
> a usable terminal?  I haven't used these types
> of programs for serial port communication since the 1990's, so it's been a
> while for me.

So, what exactly is the problem again?

If you're complaining about terminal not being set correctly, or
rows/columns not being set correctly, welcom to the world of dumb
serial devices, and they have to be set manually and correctly...
termcap does contain default rows/columns for when they aren't
provided (i.e. dumb terminals)...

Is there another issue that you're having issues with?

  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."

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