KVM (RHEL 6)

1. KVM Installation and Requirements

KVM is a full virtualization solution for x86 processors supporting hardware virtualization (Intel VT or AMD-V). It consists of two main components: A set of Kernel modules (kvm.ko, kvm-intel.ko, and kvm-amd.ko) providing the core virtualization infrastructure and processor specific drivers and a userspace program (qemu-kvm) that provides emulation for virtual devices and control mechanisms to manage VM Guests (virtual machines).

VM Guests (virtual machines), virtual storage and networks can be managed with libvirt-based and QEMU tools. libvirt is a library that provides an API to manage VM Guests based on different virtualization solutions, among them KVM and Xen. It offers a graphical user interface as well as a command line program. The QEMU tools are KVM/QEMU specific and are only available for the command line.

 

1.4. Installing KVM

You can select virtualization packages to be installed during RHEL installation by going in the “customize now” option and then selecting “virtualization” option and selecting all the options in it.

Or you can install it by following the procedure:

# yum install kvm python-virtinst libvirt libvirt-python virt-manager \

virt-viewer libguestfs-tools

After installation go to under Application -> system tools -> Virtual Machine Manager.

1.5 Disk Space

Verify you have enough disk space on the host. KVM creates image files (which look just like regular files in the file system) for each VM and assumes you are going to place them in directory /var/lib/libvirt/images.

2. KVM Limitations

2.1. General Limitations

The following general restrictions apply when using KVM:

MAC addresses:

If no MAC address is specified for a NIC, a default MAC address will be assigned. This may result in network problems when more than one NIC receives the same MAC address. It is recommended to always assure a unique MAC address has been assigned for each NIC.

Live Migration:

Live Migration is only possible between VM Host Servers with the same CPU features and no physical devices passed from host to guest. Guest storage has to be accessible from both VM Host Servers and guest definitions need to be compatible. VM Host Server and VM Guests need to have proper timekeeping installed.

User Permissions:

The management tools (Virtual Machine Manager, virsh, vm-install) need to authenticate with libvirt. In order to invoke qemu-kvm from the command line, a user has to be a member of the group kvm.

Suspending/Hibernating the VM Host Server:

Suspending or hibernating the VM Host Server system while guests are running is not supported.

 

3. KVM Support Status

3.1. Supported Features and Tools

vm-install:

Define and install VM Guests via vm-install including specifying the number of virtual processors, RAM, disk type and location, video type, keyboard mapping, NIC type, binding, MAC address, and boot method.

Restrictions: Currently only the raw, qcow2 and qed disk formats are supported. NIC creation is restricted to using Realtek, e1000 or virtio NICs.

Virtual Machine Manager:

Manage guests via Virtual Machine Manager using the following functions: autostart, start, stop, restart, pause, unpause, save, restore, clone, migrate, special key sequence insertion, guest console viewers, performance monitoring, and CPU pinning. Furthermore, static modifications of CPU, RAM, boot method, disk, NIC, mouse, display, video and host PCI and USB assignments are supported.

Restrictions: The following features are currently not supported: sound devices, qxl, vmvga (vmware), Xen video, emulated SCSI and SATA disks, vmdk storage format, Spice graphics, eepro100, ne2k_pci, pcnet, Smartcard and USB redirection.

virsh

Manage guests via the command line.

Restrictions: Requires XML descriptions as created by vm-install or virt-manager. Altering these descriptions via virsh edit is not supported. The supported virsh functionality is restricted to life cycle functions.

qemu-kvm

Manage guests via the command line. Although managing via Virtual Machine Manager should be the preferred option, qemu-kvm may be used for greater flexibility.

kvm_stat

Debugging and monitoring tool.

USB Host Device Pass-through:

A physical USB device may be passed from the VM Host Server to the VM Guest.

 

5.2. Changing a VM Guest's State with virsh

In the following examples the state of a VM Guest named “sles11” is changed.

Start

virsh -c qemu:///system start sles11

Pause

virsh -c qemu:///system suspend sles11

Reboot

virsh -c qemu:///system reboot sles11

Graceful shutdown

virsh -c qemu:///system shutdown sles11

Force shutdown

virsh -c qemu:///system destroy sles11

Turn on autostart

virsh -c qemu:///system autostart sles11

Turn off autostart

virsh -c qemu:///system autostart --disable sles11

 

 

7.2. Configuring Remote Connections

A major benefit of libvirt is the ability to manage VM Guests on different remote hosts from a central location. This section gives detailed instructions on how to configure server and client to allow remote connections.

 

Remote Tunnel over SSH (qemu+ssh)

Enabling a remote connection that is tunneled over SSH on the VM Host Server only requires the ability to accept SSH connections. Make sure the SSH daemon is started (rcsshd status) and that the ports for service SSH are opened in the firewall.

User authentication for SSH connections can be done using traditional file user/group ownership and permissions. Connecting as user root (qemu+ssh://root@mercury.example.com/system) works out of the box and does not require additional configuration on the libvirt side.

 

7.3. Connecting to a VM Host Server

In order to connect to a hypervisor with libvirt, you need to specify a uniform resource identifier (URI). This URI is needed with virsh and virt-viewer (except when working as root on the VM Host Server) and is optional for the Virtual Machine Manager. Although the latter can be called with a connection parameter (for example, virt-manager -c qemu:///system), it also offers a graphical interface to create connection URIs. 

Example Hypervisor Connection URIs

test:///default

Connect to the local dummy hypervisor. Useful for testing.

qemu:///system

Connect to the QEMU hypervisor on the local host having full access (type system). This usually requires that the command is issued by the user root.

qemu+ssh://tux@mercury.example.com/system

Connect to the QEMU hypervisor on the remote host mercury.example.com. The connection is established via an SSH tunnel.

qemu+tls://saturn.example.com/system

Connect to the QEMU hypervisor on the remote host mercury.example.com. The connection is established TLS/SSL.

 

Some features:

1. Monitoring and Migrating the VM from 1 Host to another host.

 

 

In the starting, on localhost, 2 VMs are running rhel6.2 and win2008.

To view another systems running and not running VMs, you first need to add the system you want to monitor and which is in your network.

 

To do this, go to File option and select “add connection” option.

Now a “add conection” window will be opened.

 

 

Click on “Connect to remote host”

Method SSH

Give username which is by default “root”

And give hostname. Here you can also give the IP address of the system too.

Now click on “connect”.

 

Now in the “Virtual Machine Manager” window it will show “192.168.1.20(QEMU) – Connecting”.

Now it will show a message “the authenticity of host '192.168.1.20' cant be established.

RSA key fingerprint is xx.xx.xx.xx.xx.xx.x.x.x.x.x.x.x.x.x.

are u sure u want to cont. connecting (yes/no) ?”

 

Type “yes” here.

 

Next window will be: openssh screen.

Now it will ask you the root password.

Type root password here.

root@192.168.1.20's password: redhat

And click OK.

 

 

After few moments, it will start showing second machines VMs.

 

 

Now it is showing all 3 VMs on the second system 192.168.1.20.

 

Here now you can also migrate any VM running on this machine to another machine in the network.

Just click on any VM.

Right click on it.

Click on “Migrate”.

 

Now it will ask you to specify the New Host on which you want to migrate the VM.

In this scenario, I am migrating the VM from 192.168.1.20(prakash.taashee.com) to 192.168.1.31(localhost) system.

 

Click on migrate.

Now it would migrate on the required system.

 

 

2. Adding storage in a VM:

 

This is the fresh installed windows machine image.

The Disk Management window is like this:

Check its storage details. It is showing the C-drive of 9.90 GB.

Lets say, you want to add 10GB more to it.

 

Note:  Make sure the VM is in shutoff mode.

 

To do this, on the local system you need to run a command.

 

# qemu-img resize windows.img +10GB

It will instantly show the message “Image resized”.

This 10GB size has been added in the windows and will be shown as the “Un allocated partition”.

Now if you want, you can create a whole new drive of this unallocated partition.

And you can add this free space in your C-drive.

 

For this right click on C-drive and click “extend” option.

Finally, 10GB space would be added to it and it would look like this: