Linux on KVM
 Starting your first KVM virtual machine
To start your first KVM virtual machine, first download SysRescueCD and save it to systemrescuecd.iso. Then use the following commands, which will create a 10GB qcow disk image to use for the first disk, and then the next command will start your virtual machine, booting from the CD:
# qemu-img create -f qcow2 vdisk.qcow2 10 # qemu-system-x86_64 vdisk.qcow2 -m 1024 -cdrom systemrescuecd.iso -vnc 127.0.0.1:1 -cpu host -net nic -net user VNC server running on `127.0.0.1:5900'
Now you should be able to use a VNC client to connect to 127.0.0.1:5901 (VNC session 1) and access your virtual machine.
 Networking Options
Above, networking will be enabled but will be on its own private LAN, and ping will not work. If you have a local bridge that you use for networking, the following steps will allow you use your existing bridge to provide higher-performance and full-featured network access to your virtual machine.
First, create /etc/qemu-ifup and add the following to it. Replace brlan with the name of your bridge:
#!/bin/bash ifconfig $1 0.0.0.0 promisc up brctl addif brlan $1 sleep 2
Make it executable:
# chmod +x /etc/qemu-ifup
Start the virtual machine as follows:
# qemu-system-x86_64 vdisk.qcow2 -m 1024 -cdrom systemrescuecd-x86-2.8.0.iso -cpu host -vnc 127.0.0.1:1 -net nic -net tap,id=foo
 Tweaking KVM
 VNC Output
If you wanted to have VNC listen on a different IP address or port, you can use the format -vnc IP:vncnum which will cause VNC to listen on the IP specified, and the TCP port 5900+vncnum.
 CPU Settings
By default, the KVM guest will have one CPU with one core. To change this, use -cpu host (to export all of the host's CPU features) and -smp cores=X,threads=Y, where X is the number of cores, and Y is the number of threads on each core. You can emulate more CPUs and cores than you actually have.