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Re: [atomic-devel] EC2 PV/HVM AMIs

On Mon, Jul 21, 2014 at 09:38:43PM -0400, Andy Grimm wrote:
> On Mon, Jul 21, 2014 at 4:25 PM, Matthew Miller <mattdm mattdm org> wrote:
> > On Mon, Jul 21, 2014 at 02:33:55PM -0400, Andy Grimm wrote:
> >> Fedora isn't going to stay this way for long, though  They are
> >> intending to register HVM images.  Actually, I do not believe that
> >> hvc0 is the correct console device for HVM images (I will double-check
> >> this), and there is no issue specifying more than one console device.
> >> The most recent RHEL 6 HVM image I registered specified "console=tty0
> >> console=ttyS0 console=hvc0" just to cover all the bases.  I don't know
> >> which of them was right, but I got console output.  :)
> >
> > There is, or was -- I haven't rechecked -- a bug where specifying
> > non-existent console devices caused systemd to spawn a getty for them
> > anyway, and possibly out of control.
> ouch, that's not good.  I was not aware of that one.

Indeed. If it does exist it would be nice to fix so that we have a
better chance of being able to create a unified image. 

> > Also, when multiple consoles are listed, output goes to them all, but input
> > comes from the last one. And, only last one is "/dev/console", which means
> > that programs which open and write to /dev/console (cloud-init, I'm lookin'
> > at you) are sensitive to the ordering here.
> This is really interesting.  In the image I'm currently testing (which
> is EL6, but that shouldn't matter for this particular point), I listed
> "console=hvc0 console=ttyS0 console=tty0".  Everything I've found in
> random blog posts suggests that the correct console device for HVM
> images in EC2 is ttyS0, but tty0 is the one I have listed last, and
> I'm getting cloud-init output.  I am more certain that hvc0 is *not*
> the right device, since attempts to write to it under HVM return "No
> such device or address".

For Amazon EC2 I guess it doesn't matter which one is listed last
because AFAIK there is no way to interact with the console and send it
input. You can get/read the console output, but that is it. For EL6 I use 
hvc0 for PV and ttyS0 for HVM.

Also for EC2, tty0 most likely will never be needed. I don't think
there is a way to get VGA console redirection.

- Dusty 

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