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From the perspective of the Compute service, the QEMU hypervisor is very similar to the KVM hypervisor. Both are controlled through libvirt, both support the same feature set, and all virtual machine images that are compatible with KVM are also compatible with QEMU. The main difference is that QEMU does not support native virtualization. Consequently, QEMU has worse performance than KVM and is a poor choice for a production deployment.

The typical uses cases for QEMU are

  • Running on older hardware that lacks virtualization support.

  • Running the Compute service inside of a virtual machine for development or testing purposes, where the hypervisor does not support native virtualization for guests.

To enable QEMU, add these settings to nova.conf:

compute_driver = libvirt.LibvirtDriver

virt_type = qemu

For some operations you may also have to install the guestmount utility:

On Ubuntu:

# apt-get install guestmount

On Red Hat Enterprise Linux, Fedora, or CentOS:

# yum install libguestfs-tools

On openSUSE:

# zypper install guestfs-tools

The QEMU hypervisor supports the following virtual machine image formats:

  • Raw

  • QEMU Copy-on-write (qcow2)

  • VMware virtual machine disk format (vmdk)

 Tips and fixes for QEMU on RHEL

If you are testing OpenStack in a virtual machine, you must configure Compute to use qemu without KVM and hardware virtualization. The second command relaxes SELinux rules to allow this mode of operation ( The last two commands here work around a libvirt issue fixed in Red Hat Enterprise Linux 6.4. Nested virtualization will be the much slower TCG variety, and you should provide lots of memory to the top-level guest, because the OpenStack-created guests default to 2GM RAM with no overcommit.


The second command, setsebool, may take a while.

# openstack-config --set /etc/nova/nova.conf libvirt virt_type qemu
# setsebool -P virt_use_execmem on
# ln -s /usr/libexec/qemu-kvm /usr/bin/qemu-system-x86_64
# service libvirtd restart
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