KVM is a full virtualisation solution for Linux on x86 (64-bit included) hardware containing virtualisation extensions, Intel VT or AMD-V. It consists of a loadable kernel module that provides the core virtualisation infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko.
Our server has an Intel CPU, which supports hardware virtualisation:
# grep -c vmx /proc/cpuinfo 4
We are going to use Debian Jessie.
Installation
# apt-get install qemu-kvm libvirt-bin virtinst virt-viewer ebtables dnsmasq
KVM Kernel Modules
Now, if we were to use the default 3.16 kernel which is shipped with Debian Jessie, we should have the following kernel configuration already in place:
# egrep 'KVM_INTEL|KVM_AMD' /boot/config-3.16.0-4-amd64 CONFIG_KVM_INTEL=m CONFIG_KVM_AMD=m
Therefore if the KVM kernel module is not loaded, we must load it as follows:
# modprobe kvm_intel #(for Intel processors) # modprobe kvm_amd #(for AMD processors)
In our particular case, we have kvm compiled into the kernel and therefore no module is loaded:
# egrep 'KVM_INTEL|KVM_AMD' /boot/config-4.2.6-dev CONFIG_KVM_INTEL=y # CONFIG_KVM_AMD is not set
After installing the packages, we may need to enable the libvirtd service and ensure it’s started:
# systemctl enable libvirtd # systemctl start libvirtd
We can now check our node information (4 CPUs, 12GB of RAM):
# virsh nodeinfo CPU model: x86_64 CPU(s): 4 CPU frequency: 2719 MHz CPU socket(s): 1 Core(s) per socket: 2 Thread(s) per core: 2 NUMA cell(s): 1 Memory size: 12006088 KiB
Create a New KVM Host
Create a new disk image /kvm_data/centos1.img of size 4GB and format qcow2:
# qemu-img create -f qcow2 /kvm_data/centos1.img 4G Formatting '/kvm_data/centos1.img', fmt=qcow2 size=4294967296 encryption=off cluster_size=65536 lazy_refcounts=off
Provision a new CentOS 7 virtual machine allocating 1 CPU and 1GB of RAM:
# virt-install --virt-type kvm --name=centos1 --vcpu=1 --ram=1024 \ --disk path=/kvm_data/centos1.img,size=4,format=qcow2,sparse=true \ --os-variant=rhel7 --cpuset=auto \ --graphics spice \ --cdrom /tmp/CentOS-7-x86_64-DVD-1511.iso \ --network user
If we get a “ERROR Guest name ‘centos1’ is already in use.” error, we may need to undefine the guest first:
# virsh undefine centos1
By default, QEMU invokes the -nic and -user options to add a single network adapter to the guest and provide NATed external Internet access. The host and guest will not see each other. In order to provide full network accessibility for the VM clients, you may set up a public bridge. This is beyond the scope of this article. Please check this post for details.
Get information about the disk image filename:
# qemu-img info /kvm_data/centos1.img
image: /kvm_data/centos1.img
file format: qcow2
virtual size: 4.0G (4294967296 bytes)
disk size: 1.1G
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
Get domain information:
# virsh dominfo centos1 Id: 4 Name: centos1 UUID: e6da3d3b-3526-48e1-9a0c-c16b2ac002ac OS Type: hvm State: running CPU(s): 1 CPU time: 9.7s Max memory: 1048576 KiB Used memory: 1048576 KiB Persistent: yes Autostart: disable Managed save: no Security model: none Security DOI: 0
List domains:
# virsh list --all Id Name State ------------------------------- 4 centos1 running
KVM Domain Management from the CLI
Start a (previously defined) inactive domain:
# virsh start centos1 Domain centos1 started
Connect to the guest console:
# virsh console centos1
Save a domain state to a file:
# virsh save centos1 /tmp/centos1.state Domain centos1 saved to /tmp/centos1.state
Restore a domain from a saved state in a file:
# virsh restore /tmp/centos1.state Domain restored from /tmp/centos1.state
Gracefully shutdown a domain:
# virsh shutdown centos1
If we need to make configuration changes for a domain, we can edit XML configuration:
# virsh edit centos1
Display the graphical console for a virtual machine:
# virt-viewer centos1
Autostart a domain:
# virsh autostart centos1
Disable autostart a domain:
# virsh autostart centos1 --disable
Virsh has over 180 commands, check virsh help for more information.
KVM Domain Management from the GUI
A graphical UI to manage VMs is available:
# apt-get install virt-manager
Open the Virtual Machine Manager:
# virt-manager
Referenes
https://wiki.debian.org/KVM