QEMU

BIOS and UEFI firmware[edit | edit source]

In order to utilize KVM either Vt-x or AMD-V must be supported by the processor. Vt-x or AMD-V are Intel and AMD's respective technologies for permitting multiple operating systems to concurrently execute operations on the processors.

To inspect hardware for virtualization support issue the following command:

For a period manufacturers were shipping with virtualization turned off by default in the system BIOS. Note that changing this feature in the BIOS may actually require full removal of power from the system to take effect. If restarting the system does not work try shutting down, unplugging the system and pressing the power button in an unplugged state to discharge any residual energy from the power supply unit (PSU). Reapply power to the system to verify success.

If KVM support is available there should be a "kvm" device listed at /dev/kvm. This will take effect after the system has booted to a KVM enabled kernel.

Kernel[edit | edit source]

Activate the following kernel options:

[*] Virtualization  --->
    <*>   Kernel-based Virtual Machine (KVM) support

[*] Virtualization  --->
    <M>   KVM for Intel processors support

[*] Virtualization  --->
    <M>   KVM for AMD processors support

Needed for vhost-net USE flag (recommend):

[*] Virtualization --->
    <*>   Host kernel accelerator for virtio net

Device Drivers  --->
    [*] VHOST drivers  --->
        <*>   Host kernel accelerator for virtio net

Device Drivers  --->
    [*] Network device support  --->
        [*]   Network core driver support
        <*>   Universal TUN/TAP device driver support

Needed for 802.1d Ethernet bridging:

[*] Networking support  --->
        Networking options  --->
            <*> The IPv6 protocol
            <*> 802.1d Ethernet Bridging

USE flags[edit | edit source]

Some packages are aware of the qemu USE flag.

Review the possible USE flags for QEMU:

QEMU_SOFTMMU_TARGETS="arm x86_64 sparc"
QEMU_USER_TARGETS="x86_64"

app-emulation/qemu qemu_softmmu_targets_arm qemu_softmmu_targets_x86_64 qemu_softmmu_targets_sparc
app-emulation/qemu qemu_user_targets_x86_64

app-emulation/qemu QEMU_SOFTMMU_TARGETS: arm x86_64 sparc QEMU_USER_TARGETS: x86_64

Emerge[edit | edit source]

After reviewing and adding any desired USE flags, emerge app-emulation/qemu:

Networking[edit | edit source]

For Networking configuration, see the networking options documentation.

IPv6[edit | edit source]

For IPv6 networking see the IPv6 subarticle.

Permissions[edit | edit source]

In order to run a KVM accelerated virtual machine without logging as root, add normal users to the kvm group. Replace <username> in the example command below with the appropriate user(s):

Front ends[edit | edit source]

To make life easier, there are multiple user-friendly front ends to QEMU:

auth_unix_ro = "none"
auth_unix_rw = "none"
unix_sock_group = "libvirt"
unix_sock_ro_perms = "0777"
unix_sock_rw_perms = "0770"

"kvm: already loaded the other module"[edit | edit source]

Sometimes during the early boot splash the error message "kvm: already loaded the other module" can be seen. This message indicates both the Intel and the AMD kernel virtual machine settings have been enabled in the kernel. To fix this, enable as a module or disable either the Intel or AMD KVM option specific to the system's processor in the kernel configuration. For example, if the system has an Intel processor enable the Intel KVM, then make sure the AMD KVM is set as a module (M) or is disabled (N). The relevant options to enable or disable can be found in the kernel's .config file via the CONFIG_KVM_INTEL and CONFIG_KVM_AMD variables or in the configuration section above.

Creating TUN/TAP device - No such file or directory[edit | edit source]

Sometimes this error can occur if TUN/TAP support cannot be found in the kernel. To solve this, try loading the driver:

If that works, add this to a file in /etc/modules-load.d/ to load on startup:

tun