Re: [Xen-users] VNC console access in paravirtualized domUs

["Ray Barnes" <tical.net@xxxxxxxxx>]

On Fri, Jun 6, 2008 at 5:33 AM, jim burns <jim_burn@xxxxxxxxxxxxx> wrote:

> Probably a 'chicken or the egg' problem - you probably don't get
> an /etc/X11/xorg.conf until you have a desktop you can run display device
> configuration from :-) This is usually handled by your domu installer.

I get one upon 'apt-get -y install xorg' but no mention of "fbdev" therein.

> Vnc itself requires some sort of frame buffer device, which is only supported
> in X. It's not a pv or hvm thing - it's a virtual device thing.

Got it.  How to go about that under Debian is another story.

>
> Now if you only want text output, all you need is 'xm create -c dom.cfg'. If
> you want the boot message output, you probably want to put back
> the 'console=xvc0' clause. Where you put this depends on your cfg's kernel=
> parm. If you have 'kernel='/usr/bin/pygrub', you want it in your
> domu's /boot/grub/grub.conf (or menu.lst for SuSE) at the end of the 'kernel'
> line. If you have kernel=path-to-kernel-in-dom0, you want it in the extra=
> parm of your domu's .cfg. (If you are trying to boot a 2.6.24 or higher
> kernel, this becomes hvc0 instead of xvc0. My Fedora 9 pv is pretty good
> about knowing the default, tho'.)

The tip about hvc0/xvc0 was helpful in getting Debian Lenny going; for
grins I decided to spin an image of Lenny to assist in
troubleshooting.  Regarding the framebuffer (using Lenny for
reference), I've got the xorg fbdev package installed.  I've added a
section to xorg.conf like:

Section "Device"
         Identifier "vnctest"
         Driver "fbdev"
EndSection

But as far as I can tell, the issue is that the domU does not expose
the framebuffer to the dom0:

XENBUS: Device with no driver: device/vkbd/0
XENBUS: Device with no driver: device/vfb/0
XENBUS: Device with no driver: device/console/0

I believe that's why I see "parallel0 console" in VNC.  There is no
/dev/fb0 on the domU (docs make reference to this; I've got to believe
udev would throw it up if it were configured properly).  Any ideas
there?

>
> Additionally, if you want to log in after the boot messages, you need a getty
> running on xvc0 (or hvc0). In the domu's /etc/inittab, near the end in the
> getty section, I have co:2345:respawn:/sbin/agetty xvc0 9600 vt100-nav, and
> the xvc0 device has to be listed in /etc/securetty. Personally, tho' I just
> use ssh to log in to the domu, since it adapts to my terminal size better.

Right; that's exactly what I've done under CentOS.  Understand that
this isn't in vain; I'm trying to provide console access to people who
senselessly lock themselves out of their domU, otherwise ssh would be
fine.

-Ray

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