Difference between revisions of "Managing and Monitoring Fedora based KVM Guest Systems"

Revision as of 19:20, 13 March 2008

In the previous chapter (Installing and Configuring Fedora KVM Virtualization) we covered the steps necessary to configure the Fedora operating system to act as a KVM host system and created, installed and ran a KVM guest system.

In this chapter we will explore the use of the virt-manager tool to manage the KVM guest operating systems.

Starting and Stopping KVM Guest Systems

When a KVM virtual guest system has been configured it will appear in the list of systems when the virt-manager is loaded. The virt-manager tool is launched either by selecting the Applications->System Tools->Virtual Machine Manager or from the command-line by running /usr/sbin/virt-manager. If virt-manager shows the host system as being disconnected, connect to it either by double clicking on the host in the list or right click on it and select Connect from the resulting menu.

The following screenshot shows the virt-manager tool running on a Fedora system. It lists one connected host system (localhost), and two guest virtual systems named kvm-fedora2 and virt-fedora both of which are currently shut down:

To launch a guest virtual OS, either double click on the OS in the list and then click on the Run button in the Virtual Machine Console, or right click on the system and select Run from the context menu and the double click on the machine to launch the Virtual Machine Console.

To stop a virtual machine running a guest OS it is not sufficient to simply close the Virtual Machine Console and Virtual Machine Manager windows. Doing so only closes the manager and console, leaving the guest operating system running in the background. In fact, if you try closing these windows and then restart the virt-manager tool you will see the guest OS is still listed as running, and selecting open will display the guest OS exactly as it was before you closed the console window.

To shutdown a guest OS, either shut it down using the operating system's own shut down mechanism, click on Shutdown in the Virtual Machine Console toolbar, or right click on the guest OS from the list in the virt-manager main screen and select Shutdown.

Pausing a KVM Guest Operating System

KVM provides the ability to pause and resume a running guest operating system. To pause a running system, either click the Pause button in the Virtual Machine Console toolbar, or right click the operating system in the virt-manager main screen and select Pause.

A paused guest OS may then be resumed either by clicking again on the Pause button in the Virtual Machine Console toolbar, or right click the operating system in the virt-manager main screen and select Resume.

Note that a paused guest system will not survive the reboot of the host operating system and continues to use system memory in the paused state. In the event that the host operating system is rebooted, the guest operating system will need to be restarted and cannot be resumed from its paused state.

Changing KVM Virtual Guest System Settings

During the initial configuration of the guest OS in virt-manager a number of resources such as memory allocation and CPU usage were defined. It is common to discover after the guest OS starts running that these settings need to be changed. Fortunately, virt-manager makes it easy to change these settings.

One point to note is that it is not possible to change CPU and memory settings for a currently running KVM virtual system. Be sure to shutdown the system you wish to re-configure before attempting to change these settings.

To modify the settings for a specific guest operating system, start virt-manager (Applications->System Tools->Virtual Machine Manager), select the desired guest operating system and click on the Details button. When the Virtual Machine Details dialog appears, click on the Hardware tab to view the current settings:

The hardware screen initially displays the CPU settings, allowing the number of CPUs used by the virtual machine to modified. It is recommended that the number of CPUs specified here not exceed the number of physical CPUs present in the host system.

The panel on the left allows the current displayed category to be changed. For example, to change the memory assigned to the guest system, select the Memory option and change the settings as required:

Additional disks and other devices may be added by clicking on the Add button at the bottom of the hardware category list, selecting Storage device from the Hardware type menu and clicking on Forward. Specify either a disk partition, or a file location to act as the new disk.

Monitoring Virtual Machine Performance

The virt-manager tool provides information on CPU and memory usage for each guest operating system. To view the performance graphs, select the desired guest OS in the virt-manager main window and click on Details. The Virtual Machine Details screen will display two real-time graphs showing the Memory and CPU usage for the selected guest:

In addition, the virt-manager main window displays smaller CPU graph and Memory scale next to each guest OS together with a bar indicating the percentage of overall available memory used by each operating system:

The overall performance statistic of the host operating system may similarly be viewed by selecting the host OS in virt-manager and clicking on the Detail button or selecting the Edit->Machine details... menu option.