when "subscriber" node launch before "publisher",can't get the messag

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Well then there might be a problem with the communication. That would mean the master can not contact the node after launch.

Normally it works like this:

• Subscriber -> Master (register topic, XMLRPC Node Port)
• Master -> Subscriber (ok - Already Available Publlishers)
• Publisher -> Master (register topic - XMLRPC Node Port)
• Master -> Publisher (ok)
• Master -> Subscriber (Publisher Update - newly available Publisher)

Publisher - Subscriber communication

• Subscriber -> Publisher (on XMLRPC - getTopic)
• Publisher -> (ok , topic port)
• Subscriber connects to topic port...and receives messages

Somehow your node probably not gets the Publisher Update or the Subscriber can not contact the publisher or its topic port.

Does rqt_graph get the node or is there a red circle for it, if there is a red circle, the node does not respond on it's xmlrpc port.

One thing I know that could happen when the nodes are on different computers... there could be a problem with your name resolution (/etc/hosts - DNS) That they do not find each other or just one finds the other.

Check that you can ping the computers hostnames.

ping hostname

If not put their IP-Adresses and hostnames in /etc/hosts.