Chapter 9. Configuring Virtual Machines

Chapter 9. Configuring Virtual Machines¶

Contents

9.1. Adding a CD/DVD-ROM Device with Virtual Machine Manager
9.2. Adding a Floppy Device with Virtual Machine Manager
9.3. Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager
9.4. Clock Settings

9.1. Adding a CD/DVD-ROM Device with Virtual Machine Manager¶

KVM supports CD or DVD-ROMs in VM Guest either by directly accessing a physical drive on the VM Host Server or by accessing ISO images. To create an ISO image from an existing CD or DVD, use dd:

dd if=/dev/cd_dvd_device of=my_distro.iso bs=2048

To add a CD/DVD-ROM device to your VM Guest proceed as follows:

Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the configuration screen with View+Details.
Click Add Hardware and choose Storage in the pop-up window. Proceed with Forward.
Change the Device Type to IDE CDROM.
Select Select Managed or Other Existing Storage.
1. To assign the device to a physical medium, enter the path to the VM Host Server's CD/DVD-ROM device (for example, /dev/cdrom) next to the Browse button. Alternatively you may use the Browse button to open a file browser and then click Browse Local to select the device. Assigning the device to a physical medium is only possible, when the Virtual Machine Manager was started on the VM Host Server.
2. To assign the device to an existing image, click Browse to choose an image from a storage pool. If the Virtual Machine Manager was started on the VM Host Server, you may alternatively choose an image from another location on the file system by clicking Browse Local. Select an image and close the file browser with Choose Volume.
Proceed with Forward to review the settings. Apply them with Finish, Yes, and Apply.
Reboot the VM Guest to make the new device available. For further information also see Section 9.3, “Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager”.

9.2. Adding a Floppy Device with Virtual Machine Manager¶

Currently KVM only supports the use of floppy disk images—using a physical floppy drive is not supported. Create a floppy disk image from an existing floppy using dd:

dd if=/dev/fd0 of=/var/lib/libvirt/images/floppy.img

To create an empty floppy disk image use one of the following commands:

# raw image
dd if=/dev/zero of=/var/lib/libvirt/images/floppy.img bs=512 count=2880

# FAT formatted image
mkfs.msdos -C /var/lib/libvirt/images/floppy.img 1440

To add a floppy device to your VM Guest proceed as follows:

Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the configuration screen with View+Details.
Click Add Hardware and choose Storage in the pop-up window. Proceed with Forward.
Change the Device Type to Floppy Disk.
Choose Select Managed or Other Existing Storage and click Browse to choose an existing image from a storage pool. If Virtual Machine Manager was started on the VM Host Server, you may alternatively choose an image from another location on the file system by clicking Browse Local. Select an image and close the file browser with Choose Volume.
Proceed with Forward to review the settings. Apply them with Finish, Yes, and Apply.
Reboot the VM Guest to make the new device available. For further information also see Section 9.3, “Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager”.

9.3. Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager¶

Regardless whether you are using the VM Host Server's physical CD/DVD-ROM device or an ISO image: before you can change the media or image of an existing device in the VM Guest, you first need to disconnect the media from the guest.

Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the configuration screen with View+Details.
Choose the Floppy or CD/DVD-ROM device and “eject” the media by clicking Disconnect.
To “insert” a new media, click Connect.
1. If using the VM Host Server's physical CD/DVD-ROM device, first change the media in the device (this may require to unmount it before it can be ejected). Then choose CD-ROM or DVD and select the device from the drop-down list.
2. If using an ISO image, choose ISO image Location and select an image by clicking Browse. When connecting from a remote host, you may only choose images from existing storage pools.
Click OK to finish. The new media can now be accessed in the VM Guest.

9.4. Clock Settings¶

Keeping the correct time in a VM Guest is one of the more difficult aspects of virtualization. Keeping the correct time is especially important for network applications and is also a prerequisite to do a live migration of a VM Guest.

	Time Keeping on the VM Host Server
It is strongly recommended to ensure the VM Host Server keeps the correct time as well, for example, by utilizing NTP (see Chapter 27, Time Synchronization with NTP (↑Reference) for more information).

9.4.1. Using `kvm_clock`¶

KVM provides a para-virtualized clock which is currently supported by SUSE Linux Enterprise Server 10 SP3 and newer and RedHat Enterprise Linux 5.4 and newer via the kvm_clock driver. It is strongly recommended to use kvm_clock when available.

Use the following command inside a VM Guest running Linux to check whether the driver kvm_clock has been loaded:

~ # dmesg | grep kvm-clock
[    0.000000] kvm-clock: cpu 0, msr 0:7d3a81, boot clock
[    0.000000] kvm-clock: cpu 0, msr 0:1206a81, primary cpu clock
[    0.012000] kvm-clock: cpu 1, msr 0:1306a81, secondary cpu clock
[    0.160082] Switching to clocksource kvm-clock

To check which clock source is currently used, run the following command in the VM Guest. It should output kvm-clock:

echo /sys/devices/system/clocksource/clocksource0/current_clocksource

	`kvm-clock` and NTP
When using `kvm-clock`, it is not recommended to use NTP in the VM Guest, as well. Using NTP on the VM Host Server, however, is still recommended.

9.4.2. Other Time Keeping Methods¶

The para-virtualized kvm-clock is currently not available for SUSE Linux Enterprise Server 9 and Windows operating systems. For Windows, use the Windows Time Service Tools for time synchronization (see http://technet.microsoft.com/en-us/library/cc773263%28WS.10%29.aspx for more information).

Correct time keeping in SUSE Linux Enterprise Server 9 SP4 can be achieved by using special boot parameters:

32-bit Kernel:clock=pmtmr

64-bit Kernel:ignore_lost_ticks