Re: [Qemu-devel] How to get target system display with qemu -nographic option?

[David Barrett <dbarrett@quinthar.com>]

Atoosah wrote:
>     When -nographic is specified, no graphical window is created.  The only
>     way to see the graphics window is using the VNC option.
> 
> If I run the program with graphics enabled (i.e. no -nographic option) I 
> get the login prompt and then the password. From then on, the display is 
> in shell prompt mode. So, does -nographic mean that I won't be able to 
> access this display? If so, it seems very limiting without being able to 
> run experiments on our guest machine.

Ah, "graphics" means "display" -- it doesn't matter whether your guest 
VM is running X or using a simple terminal, it all looks like one big 
graphic to qemu.

Said another way, "-nographic" disables the display entirely, whether 
that display is used for graphics or text.


>     Furthermore, when -nographic is specified, I think "-monitor" defaults
>     to "serial", meaning the actual serial output is overridden by the qemu
>     monitor.  To change this, look at "-monitor" and direct it somewhere
>     else (such as to a TCP stream).
> 
> I'd appreciate if you'd explain a bit more what you mean by "serial 
> output is overridden by the qemu
> monitor"..

The "monitor" is the command-line interface to control qemu (start and 
stop the VM, snapshots, etc).  Normally, you can get to it with the 
Control-Alt key combination: the display window switches to a terminal 
showing the qemu monitor.

However, when "-nographic" is specified, there is no display window. 
So, it pretends you specified "-monitor serial", which enables access to 
the qemu monitor via the virtual serial cable.  Unfortunately, that 
means that you can no longer access the *real* virtual serial cable.

So, when you specify -nographic, I think if you just also specify 
"-monitor none" then it'll disable the qemu monitor entirely and leave 
the virtual serial port alone, letting you log on to your VM through the 
virtual serial cable as you expect.


I *think* this is accurate, but I honestly haven't logged on to a qemu 
vm via the serial port before (I just set up SSH), so there's some 
guesswork involved.  Take a look at the documentation for "-serial" and 
"-monitor" and that should shed some light.



>     Does this help?
> 
> 
> Thank you. I'm still looking at the vnc option. Just to make sure the 
> /etc/inittab that is modified (with 7:2345:respawn:/sbin/mgetty ttyS0 
> 9600 vt100-nav) should be the guests or the hosts? I'm a newbie in this 
> area, so any help would be appreciated.

I don't know what you're trying to do with /etc/inittab.  That doesn't 
mean it's wrong, it just means I've never found it necessary to go that 
route.  I'm guessing you should probably undo all your changes there and 
just stick with whatever was the default, and then use the "-nographic 
-monitor none" option I mention above.

-david