Xen PV/HVM

CFGS=/home/xen/vm*/;for cfg in $CFGS;do xm create $cfg*.cfg;done

OpenVZ

CFGS=`vzlist -S -Ho ctid`;for cfg in $CFGS;do vzctl start $cfg;done

KVM

CFGS=/home/kvm/kvm*/;for cfg in $CFGS;do virsh create $cfg*.xml;done