qemu/docs/qmp

QEMU Machine Protocol
=====================

Introduction
------------

The QEMU Machine Protocol (QMP) allows applications to operate a
QEMU instance.

QMP is JSON[1] based and features the following:

- Lightweight, text-based, easy to parse data format
- Asynchronous messages support (ie. events)
- Capabilities Negotiation

For detailed information on QMP's usage, please, refer to the following files:

o qmp-spec.txt QEMU Machine Protocol current specification
o qmp-commands.txt QMP supported commands (auto-generated at build-time)
o qmp-events.txt List of available asynchronous events

[1] http://www.json.org

Usage
-----

You can use the -qmp option to enable QMP. For example, the following
makes QMP available on localhost port 4444:

$ qemu [...] -qmp tcp:localhost:4444,server,nowait

However, for more flexibility and to make use of more options, the -mon
command-line option should be used. For instance, the following example
creates one HMP instance (human monitor) on stdio and one QMP instance
on localhost port 4444:

$ qemu [...] -chardev stdio,id=mon0 -mon chardev=mon0,mode=readline \
-chardev socket,id=mon1,host=localhost,port=4444,server,nowait \
-mon chardev=mon1,mode=control,pretty=on

Please, refer to QEMU's manpage for more information.

Simple Testing
--------------

To manually test QMP one can connect with telnet and issue commands by hand:

$ telnet localhost 4444
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
{
"QMP": {
"version": {
"qemu": {
"micro": 50,
"minor": 6,
"major": 1
},
"package": ""
},
"capabilities": [
]
}
}

{ "execute": "qmp_capabilities" }
{
"return": {
}
}

{ "execute": "query-status" }
{
"return": {
"status": "prelaunch",
"singlestep": false,
"running": false
}
}

Please, refer to the qapi-schema.json file for a complete command reference.

QMP wiki page
-------------

http://wiki.qemu-project.org/QMP