P{font-size:10pt; line-height:16; margin-left:0; margin-top:0; margin-right:0; margin-bottom:0; font-family:gulim;} (English is not my first language Sorry for my poor English )   OS :  Linux nc233 2632-220171el6x86_64 #1 SMP Tue May 15 17:16:46 CDT 2012 x86_64 x86_64 x86_64 GNU/Linux CentOS release 63 (Final) open vswitch : 11190 virsh : 100 ibvirtd (libvirt) : 100   I have tried to see what the virsh setting can do to open vswitch(ovs) until now I had installed open vswitch from a source, not by using rpm or rpm build of the source (I had tried to do 'ovs rpm build' described at INSTALLRHEL included in ovs, But i failed to do it)   What i tried is this(http://blogscottloweorg/2012/11/07/using-vlans-with-ovs-and-libvirt/)  I installed and started up ovs and it looked like properly working I could create and delete bridges and ports with 'ovs-vsctl'    1 what i created before running 'virsh net-define'  -------------------------------------------- # ovs-vsctl show 76d9d6aa-cfce-4868-bf99-7d16bcfe38eb     Bridge "br0"         Port "br0"             Interface "br0"                 type: internal         Port "eth1"             Interface "eth1" --------------------------------------------     2 And then runned 'virsh net-define netxml' 'netxml' i used -------------------------------------------- <network>     <name>ovs-network</name>     <forward mode='bridge'/>     <bridge name='br0'/>     <virtualport type='openvswitch'/>     <portgroup name='vlan-01' default='yes'>     </portgroup>     <portgroup name='vlan-02'>         <vlan>         <tag id='2'/>         </vlan>     </portgroup>     <portgroup name='vlan-03'>         <vlan>         <tag id='3'/>         </vlan>     </portgroup>     <portgroup name='vlan-all'>         <vlan trunk='yes'>         <tag id='2'/>         <tag id='3'/>         </vlan>     </portgroup> </network> --------------------------------------------     3 vmxml which was used for 'virsh define vmxml' -------------------------------------------- <domain type="kvm">     <name>vm</name>     <memory>1048576</memory>     <vcpu>1</vcpu>     <os>         <type arch="x86_64" machine="pc">hvm</type>                 <boot dev="hd"/>     </os>     <features>         <acpi/>         <apic/>         <pae/>     </features>     <clock mode="localtime">         <timer name="rtc" tickpolicy="catchup" wallclock="guest"/>         <timer name="hpet" present="no"/>     </clock>     <devices>         <!--<emulator>/usr/libexec/qemu-kvm</emulator>-->         <emulator>/usr/bin/qemu-system-x86_64</emulator>         <!--<disk device="disk" type="block">-->         <disk device="disk" type="file">             <!--<driver cache="none" name="qemu" type="qcow2"/>-->             <driver cache="writeback" io="threads" name="qemu" type="qcow2"/>             <source file="/root/img/vmimg"/>             <target bus="virtio" dev="vda"/>         </disk>         <interface type="network">             <mac address="d2:0d:45:a3:92:ea"/>             <source network='ovs-network' portgroup='vlan-02'/>         </interface>         <console type="pty">             <target port="0"/>         </console>         <input bus="usb" type="tablet"/>         <input bus="ps2" type="mouse"/>         <graphics autoport="yes" keymap="en-us" listen="0000"             port="-1" type="vnc"/>     </devices> </domain> --------------------------------------------     4 runned 'virsh start vm', and failed (messages had not been printed in english at my server, so i googled and tried to choose simillar sentecne which were shown in libvirt related threads please consider it) ----------------------------------------- #virsh start vm error : Failled to start domain vm error : Unable to add port vnet0 to OVS bridge br0 -----------------------------------------     At that time, /var/log/libvirt/libvirtdlog  (these are also translated) ----------------------------------------- 2013-05-23 04:32:14588+0000: 11455: error : virNetDevGetMTU:343 : Cannot get interface MTU on 'ovsbr0': No such device  2013-05-23 04:32:14678+0000: 11455: error : virExecWithHook:419 : Cannot find 'ovs-vsctl' in path: No such file or directory 2013-05-23 04:32:14679+0000: 11455: error : virNetDevOpenvswitchRemovePort:173 : Unable to delete port (null) from OVS: command does not allowed -----------------------------------------     I think above errors comes from install location of OVS as written in libvirtdlog How can i solve that by hands? (I'm also trying to solve the problem by installing ovs, using rpm build) There are not only fedora or ubuntu linux, so the solution may exist Are there a way to get libvirt to recognize ovs-vsctl? (As i mentioned above, ovs-vsctl and ovs are properly working)   Thank you for reading