Problem about opening webcam(logitech C920)

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I followed this website http://answers.ros.org/question/19765... ,try to open my webcam. There are some errors about comand

$ rosrun usb_cam usb_cam_node

It shows error message like the following.

[ INFO] [1459206531.320684602]: using default calibration URL
[ INFO] [1459206531.321520602]: camera calibration URL: file:///home/udooer/.ros/camera_info/head_camera.yaml
[ INFO] [1459206531.322092602]: Unable to open camera calibration file 
[/home/udooer/.ros/camera_info/head_camera.yaml]
[ WARN] [1459206531.322306602]: Camera calibration file /home/udooer/.ros/camera_info/head_camera.yaml not found.
[ INFO] [1459206531.322585935]: Starting 'head_camera' (/dev/video0) at 640x480 via mmap (yuyv) at 30 FPS
[ERROR] [1459206531.327861602]: Cannot open '/dev/video0': 11, Resource temporarily unavailable

I have tried to open my camera (logitech C920) with guvcview successfully. However,it still can't work on ROS .