Error: Acquire running lock failed: 256

I recently encountered this problem on a guest VM running on OVM 3.1.1.

The Oracle VM Manager stated machine status as UNKNOWN so I could not start nor stop the VM giving me error while performing any operation on it.

Further investigation above task details returned this error:

Error: Acquire running lock failed: 256

I connected via SSH to one of Oracle VM servers and run the following command:

[root@orclvmsrv1 ~]# xm list


Name                                        ID   Mem VCPUs      State   Time(s)
0004fb00000600007fbdb52a1b566a74            15  4096     1     -b----    229.6
Domain-0                                     0   726    12     r-----  62921.7

This command returns all VMs (referred by VM ID) and theyr corresponding state.

For further informations on xm command I suggest you to visit this page: xm man

To stop the guest VM run:

xm shutdown VIRTUAL_MACHINE_ID

In this case:

[root@orclvmsrv1 ~]# xm shutdown 0004fb00000600007fbdb52a1b566a74

The guest VM shutdowns and should be correctly recognized as "Stopped" by VM Manager.

This solved my issue and I was able to start again using VM Manager.