Unable to start VM in gnome-boxes

[Matthew Ames]

1) Ubuntu Release Information
Description: Ubuntu Bionic Beaver (development branch)
Release: 18.04

2) Package Information
gnome-boxes:
  Installed: 3.27.92-1
  Candidate: 3.27.92-1
  Version table:
 *** 3.27.92-1 500
        500 http://gb.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

3) What I expect to happen:
VMs launch successfully within gnome-boxes.

4) What happens instead.

Since upgrading to Ubuntu 18.04, I have not be able to start any VMs. Running gnome-boxes from the terminal shows the following error:

(gnome-boxes:7430): Boxes-WARNING **: 10:31:57.204: machine.vala:620: Failed to start bionic-desktop-amd64(1): Unable to start domain: unsupported configuration: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

Please also find attached the troubleshooting log directly from Boxes.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-boxes 3.27.92-1
ProcVersionSignature: Ubuntu 4.15.0-13.14-generic 4.15.10
Uname: Linux 4.15.0-13-generic x86_64
ApportVersion: 2.20.9-0ubuntu2
Architecture: amd64
CurrentDesktop: ubuntu-communitheme:ubuntu:GNOME
Date: Thu Mar 29 10:35:07 2018
InstallationDate: Installed on 2017-10-24 (155 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Release amd64 (20171018)
SourcePackage: gnome-boxes
UpgradeStatus: Upgraded to bionic on 2018-03-21 (8 days ago)

[Matthew Ames (supermatt)]

Update: adding myself to the kvm group fixes this issue.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Scott M (sgmaurin)]

Yes, the same thing has been happening to me since the Bionic upgrade:

Terminal warning is the same:
(gnome-boxes:2678): Boxes-WARNING **: 00:48:02.973: machine.vala:629: Failed to start Win10 Home: Unable to start domain: unsupported configuration: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

(gnome-boxes:2678): Boxes-WARNING **: 00:48:34.093: machine.vala:629: Failed to start Fedora 27: Unable to start domain: unsupported configuration: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

Virt-manager gives me this:
Error starting domain: unsupported configuration: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 89, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 125, in tmpcb
    callback(*args, **kwargs)
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 82, in newfn
    ret = fn(self, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/domain.py", line 1508, in startup
    self._backend.create()
  File "/usr/lib/python2.7/dist-packages/libvirt.py", line 1062, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: unsupported configuration: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

All working fine before upgrade.

[Scott M (sgmaurin)]

Matthew, just to verify, did you have to log out and log in for that to work?
I added myself to the kvm group but still get the same error.
Have a couple of tasks running and I can't reboot just yet.

[Matthew Ames (supermatt)]

This may come a little later than you would have liked, but you can use the command "newgrp kvm" from a terminal window, and then launch gnome-boxes from that self-same terminal window.

[Scott M (sgmaurin)]

After adding myself to the kvm group, then rebooting, I can confirm that Gnome Boxes is working for me now.