Hello, I tried to setup UserDefinedVMProperties to disable macspoofing for a vm that has to work as hypervisor. Then I remembered suggestion of Simone about creating vnic profile as an alternate method and set there the filter. I think I have done something wrong because if I create now a new vm and try to power on it I get VM test is down with error. Exit message: Hook Error: ('',). Perhaps I failed the syntax to reset the value of UserDefinedVMProperties ? I used [root@ovirt ~]# engine-config -s "UserDefinedVMProperties=" Please select a version: 1. 4.1 2. 3.6 3. 4.0 4. 4.2 4 [root@ovirt ~]# engine-config -g UserDefinedVMProperties UserDefinedVMProperties: version: 4.1 UserDefinedVMProperties: version: 3.6 UserDefinedVMProperties: version: 4.0 UserDefinedVMProperties: version: 4.2 [root@ovirt ~]# systemctl restart ovirt-engine [root@ovirt ~]# What could be wrong? Old created VMs start without problem. In the middle I updated the engine from 4.2.5.2 to 4.2.5.3 and also hypervisor packages, where vdsm has remained at level Aug 03 23:55:09 Updated: vdsm-4.20.35-1.el7.x86_64 In particular: [root@ovirt01 ~]# rpm -qa|grep vdsm vdsm-jsonrpc-4.20.35-1.el7.noarch vdsm-common-4.20.35-1.el7.noarch vdsm-hook-nestedvt-4.20.35-1.el7.noarch vdsm-yajsonrpc-4.20.35-1.el7.noarch vdsm-hook-ethtool-options-4.20.35-1.el7.noarch vdsm-hook-vhostmd-4.20.35-1.el7.noarch vdsm-hook-vmfex-dev-4.20.35-1.el7.noarch vdsm-client-4.20.35-1.el7.noarch vdsm-4.20.35-1.el7.x86_64 vdsm-hook-vfio-mdev-4.20.35-1.el7.noarch vdsm-api-4.20.35-1.el7.noarch vdsm-hook-fcoe-4.20.35-1.el7.noarch vdsm-network-4.20.35-1.el7.x86_64 vdsm-hook-openstacknet-4.20.35-1.el7.noarch vdsm-python-4.20.35-1.el7.noarch vdsm-http-4.20.35-1.el7.noarch [root@ovirt01 ~]# The error on hypervisor: 2018-08-21 15:21:28,760+0200 ERROR (vm/eaaee084) [virt.vm] (vmId='eaaee084-1949-4aae-85c2-6bf46fce7cef') The vm start process failed (vm:94 2) Traceback (most recent call last): File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 871, in _startUnderlyingVm self._run() File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2864, in _run self._buildDomainXML(), File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2253, in _buildDomainXML dom, self.id, self._custom['custom']) File "/usr/lib/python2.7/site-packages/vdsm/virt/domxml_preprocess.py", line 240, in replace_device_xml_with_hooks_xml dev_custom) File "/usr/lib/python2.7/site-packages/vdsm/common/hooks.py", line 136, in before_device_create params=customProperties) File "/usr/lib/python2.7/site-packages/vdsm/common/hooks.py", line 122, in _runHooksDir raise exception.HookError(err) HookError: Hook Error: ('',) 2018-08-21 15:21:28,760+0200 INFO (vm/eaaee084) [virt.vm] (vmId='eaaee084-1949-4aae-85c2-6bf46fce7cef') Changed state to Down: Hook Error: ('',) (code=1) (vm:1682) I found this, but it doesn't seem related: https://bugzilla.redhat.com/show_bug.cgi?id=1518703 Thanks in advance for any hint, Gianluca