[[!meta title="How to control (shutdown) Virtual machines from Qemu/KVM via commandline"]]

## Introduction

When you have read
[[the article about tunneling a vnc socket over ssh|tunneling-qemu-kvm-unix-socket-via-ssh]],
you already know that I am a fan of using simple technologies like Unix 
sockets and ssh to access virtual machine information.

I am currently in a project to create a new virtual machine infrastructure
based on Qemu/KVM. The problem we were facing is "How to shutdown a virtual
machine, when the host is being shut down".

## Background

Qemu/KVM has a so called 
[monitor](https://en.wikibooks.org/wiki/QEMU/Monitor) to control
the VM. Usually this monitor is reachable from the VNC socket
(or whatever you use to view the console) by pressing
Ctrl-Alt-2.

This is inappropriate for automatic shutdown (I'm not in the mood
to script vnc sessions currently), so there must be a better solution.


## The solution

Qemu/KVM is able to redirect the monitor to a "character device".
There are ways to create a character device with Qemu/KVM and then
attach the monitor to it, but you can have it more easy by connecting
the monitor directly to a UNIX socket:

    qemu-kvm ... -monitor unix:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor,server,nowait

This way we can connect (and control!) Qemu/KVM using
[socat](http://www.dest-unreach.org/socat/]:

    socat - UNIX-CONNECT:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor

And when we can connect to it, we can also shutdown a virtual machine:

    echo system_powerdown | socat - UNIX-CONNECT:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor

Or we could reset it:

    echo system_reset | socat - UNIX-CONNECT:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor

## The full implementation

The full command line for running a VM as we do it in this project looks like this:

    [root@kvm-hw-inx01 kvmtest-vm-inx01.intra.local.ch]# cat start
    #!/bin/sh
    /usr/libexec/qemu-kvm -m 65536 \
        -hda /opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/system-disk \
        -vnc unix:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/vnc \
        -boot order=nc \
        -net nic,macaddr=00:16:3e:00:00:2d,vlan=200 \
            -net tap,script=/opt/local.ch/sys/kvm/bin/ifup-pz,downscript=/opt/local.ch/sys/kvm/bin/ifdown,vlan=200 \
        -net nic,macaddr=00:16:3e:00:00:2e,vlan=300 \
            -net tap,script=/opt/local.ch/sys/kvm/bin/ifup-fz,downscript=/opt/local.ch/sys/kvm/bin/ifdown,vlan=300 \
        -smp 16 \
        -name kvmtest-vm-inx01.intra.local.ch \
        -enable-kvm \
        -monitor unix:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor,server,nowait

As the VMs are currently not performing as well as they should, we will do
some investigations into performance tuning of Qemu/KVM. So stay tuned, if
you are interested in this topic.

[[!tag localch unix vm]]