Is it possible to use roslaunch without starting roscore?

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@Dragonslayer, on the jetson nano I setup (for instance) ROS_MASTER_URI=http://10.10.10.10 and ROS_HOSTNAME=10.10.10.10 I start roslaunch appli appli.launch Now on my Laptop i will setup: ROS_MASTER_URI=http://10.10.10.10 and ROS_HOSTNAME=10.10.10.9 and what I want is that the application spawn by roslaunch get topics from the application on the jetson nano. Unfortunately when I run roslaunch on my laptop, ROS is starting a roscore locally which means that I cannot access the topics published by the application of the jetson nano. Do you know if there is any possibility to prevent roslaunch to start a roscore?

If ROS_MASTER_URI and ROS_IP/ROS_HOSTNAME are set correctly, then the answer from @Dragonslayer is correct, roslaunch on the computer that shouldn't run master should not start a master. To answer the question in the comment above, you could try adding --wait to your roslaunch call to cause it to wait for a master before launching

@fabriceN I came across lots of people with issues getting this to run. For some a simple restart did the trick. Iam also not sure if launching the core on the jetson and after that "setup:" the stuff on the laptop might be the problem, could be the the roscore start sents a trigger or something like that, that is missed if you only setup the laptop after the core start etc. Of course turning off the firewalls (or preparing them in a way that data can flow) is absolut relevant. As I mentioned I have this in my bashrc`s so it sets itself up and that works fine, also for others. Pinging works? @jarvisschultz good idea "--wait".