Re: [Qemu-devel] Getting VM state from outside QEMU?

[John Snow <jsnow@redhat.com>]

On 04/07/2015 09:31 AM, Erik Rull wrote:
> Hi all,
>
> I need a pretty simple way to get the current state of the VM running in QEMU -
> I only need the VM state (e.g. running, paused,...). Since my environment does
> not have any perl, python or other high level scripting capabilities, a simple
> way e.g. via a shell script would be nice. QEMU is running daemonized, so
> interacting with the qemu console is not possible.
> Are there any usable entries in /proc, /dev or /sys that could be used?
>
> Thanks.
>
> Best regards,
>
> Erik
>

Assuming this is some sort of embedded system under which python is not 
an option:

You'll need to use the monitor interface (-monitor), and set it to a 
pipe. you can echo commands into the pipe ("info status") and read lines 
out of it.

try:

mkfifo monitor.out
mkfifo monitor.in
./qemu-system-blah -monitor pipe:monitor &
echo "info status" > monitor.in
read $line < monitor.out # 'info status'
read $line < monitor.out # 'VM status: running'

And now you've got e.g. "VM status: running" in $line. Use whichever 
shell tricks to distill this down as needed.

Warning: this is using the human monitor protocol, which as the name 
implies, is not meant for you to be scraping it with tools. It could 
change arbitrarily in the future and shouldn't be used in production.

Really recommend the QMP interface and something capable of 
sending/reading JSON for programmatic scripting of QEMU. Check out 
scripts/qmp.py for a nice library for sending/receiving these sorts of 
things.

Alternatively you can use a similar fifo trick for -qmp and try to parse 
the answers you get with sed/awk/bash regex etc.