No link between publisher and subscriber nodes

asked 2014-05-29 04:35:12 -0500

IvanV gravatar image


We are running a system with two computers (one of them as master). Both systems are Groovy over Ubuntu server 12.04. The system was actually running without problems before and the issue has appeared after restoring the system on the master computer after a hardware failure. No change has been made to the nodes or the launch files.

The extrange issue we are facing is that a subscriber node does not get the messages published by a publisher node. So far, we have suffered this problem two times, which I'll describe in more detail:

  1. An ueye node publishing images and camera info and a ar_track_alvar subscribed to both topics. Both nodes running in the same computer.
  2. A custom control node publishing Twist messages into a /cmd_vel topic, and another custom node subscribed to the same /cmd_vel topic. Each node is running in a different computer.

In both cases, error is the same:

  • Both nodes are running without giving any error.
  • Both nodes report to be publishing/subscribed to the correct node.
  • Messages are being published correctly in their respective topics.
  • Subscriber node does not receive any message.
  • rxgraph shows that both nodes are publishing/subscribed to the correct node BUT it doesn't show any link between them in the graph.

It doesn't seem to be a problem of communication with the master, as in the first case both nodes are running in the same computer. Also, network setting are correct and the different topics can be echoed without problems from any computer. ROS_MASTER_URI, ROS_IP and ROS_HOSTNAME variables are correctly set in both computers.

Moreover, when the two nodes of the first case are launched in separated launch files instead of both in the same one, the problem does not occur. However, in the second case, the subscriber node is already running much before the publisher node is launch.

We have run out of ideas trying to guess the source of this problem, so any help would be welcome.

Thank you and best regards,

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