72 lines
2.9 KiB
Text
72 lines
2.9 KiB
Text
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[[!meta title="How to control (shutdown) Virtual machines from Qemu/KVM via commandline"]]
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## Introduction
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When you have read
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[[the article about tunneling a vnc socket over ssh|tunneling-qemu-kvm-unix-socket-via-ssh]],
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you already know that I am a fan of using simple technologies like Unix
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sockets and ssh to access virtual machine information.
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I am currently in a project to create a new virtual machine infrastructure
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based on Qemu/KVM. The problem we were facing is "How to shutdown a virtual
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machine, when the host is being shut down".
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## Background
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Qemu/KVM has a so called
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[monitor](https://en.wikibooks.org/wiki/QEMU/Monitor) to control
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the VM. Usually this monitor is reachable from the VNC socket
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(or whatever you use to view the console) by pressing
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Ctrl-Alt-2.
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This is inappropriate for automatic shutdown (I'm not in the mood
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to script vnc sessions currently), so there must be a better solution.
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## The solution
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Qemu/KVM is able to redirect the monitor to a "character device".
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There are ways to create a character device with Qemu/KVM and then
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attach the monitor to it, but you can have it more easy by connecting
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the monitor directly to a UNIX socket:
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qemu-kvm ... -monitor unix:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor,server,nowait
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This way we can connect (and control!) Qemu/KVM using
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[socat](http://www.dest-unreach.org/socat/]:
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socat - UNIX-CONNECT:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor
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And when we can connect to it, we can also shutdown a virtual machine:
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echo system_powerdown | socat - UNIX-CONNECT:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor
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Or we could reset it:
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echo system_reset | socat - UNIX-CONNECT:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor
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## The full implementation
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The full command line for running a VM as we do it in this project looks like this:
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[root@kvm-hw-inx01 kvmtest-vm-inx01.intra.local.ch]# cat start
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#!/bin/sh
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/usr/libexec/qemu-kvm -m 65536 \
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-hda /opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/system-disk \
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-vnc unix:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/vnc \
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-boot order=nc \
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-net nic,macaddr=00:16:3e:00:00:2d,vlan=200 \
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-net tap,script=/opt/local.ch/sys/kvm/bin/ifup-pz,downscript=/opt/local.ch/sys/kvm/bin/ifdown,vlan=200 \
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-net nic,macaddr=00:16:3e:00:00:2e,vlan=300 \
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-net tap,script=/opt/local.ch/sys/kvm/bin/ifup-fz,downscript=/opt/local.ch/sys/kvm/bin/ifdown,vlan=300 \
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-smp 16 \
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-name kvmtest-vm-inx01.intra.local.ch \
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-enable-kvm \
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-monitor unix:/opt/local.ch/sys/kvm/vm/kvmtest-vm-inx01.intra.local.ch/monitor,server,nowait
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As the VMs are currently not performing as well as they should, we will do
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some investigations into performance tuning of Qemu/KVM. So stay tuned, if
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you are interested in this topic.
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[[!tag localch unix vm]]
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