How to disable the output of one node

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More than two years later, I came into the same issue with the usb_cam package. Below I propose two solutions, a general one, and a package-specific one.

General solution to mute rosrun output

A possible solution when launching a node from the command line, is to redirect the output (find a brief introduction to the topic and a useful cheat-sheet here) of the node by using

rosrun package_name node_name 2>&-

With this, one can run the node and see the [INFO] messages, while muting the unwanted warnings/errors.

Avoid usb_cam_node errors passing the right params at launch

Inspecting the usb_cam-test.launch file, I have noticed the following parameters being passed to the usb_cam_node at launch:

<node pkg="usb_cam" name="usb_cam_node" type="usb_cam_node">
        <param name="video_device" value="/dev/video0" />
        <param name="image_width" value="640" />
        <param name="image_height" value="480" />
        <param name="pixel_format" value="yuyv" />
        <param name="color_format" value="yuv422p" />
        <param name="camera_frame_id" value="usb_cam" />
        <param name="io_method" value="mmap"/>
 </node>

In my case, this set of params solved the warning messages.

Any explanation of the meaning of the parameters (and possibly of those to be held accountable for the warnings) is very welcome! I will do my best to update the answer with more insights if I have the occasion to dig a little bit more into this topic.

Have you tried including output="log" inside the corresponding <node> tag in your launch file?

For instance

<launch>
  <node name="usb_cam" pkg="usb_cam" type="usb_cam_node" output="log"/>
</launch>

From the documentation at http://wiki.ros.org/roslaunch/XML/node:

output="log|screen"(optional)
If 'screen', stdout/stderr from the node will be sent to the screen. If 'log', the stdout/stderr output will be sent to a log file in $ROS_HOME/log, and stderr will continue to be sent to screen. The default is 'log'.