安装kvm，用virt-manager启动时报错如下：

Traceback (most recent call last):
  File "/usr/share/virt-manager/virt-manager.py", line 383, in <module>
    main()
  File "/usr/share/virt-manager/virt-manager.py", line 286, in main
    raise gtk_error
RuntimeError: could not open display

kvm虚拟机virt-manager启动报错