Does a roslaunch start roscore when needed?

asked 2015-09-05 07:54:55 -0500

Nap
302 ●24 ●31 ●36

updated 2015-09-05 12:48:04 -0500

[Ubuntu 14.04, ROS Hydro]

As per the title.
It seems to me that it does. However I would like to have it confirmed. (Sorry if this is silly question.)

Cheers, Nap
(Thank you for the answer and explanations.)

answered 2015-09-05 08:43:01 -0500

Boris

3060 ●32 ●57 ●83 http://people.idsia.ch/~gromov

Yes, it does. If there is no roscore already running.

As per Wiki on roslaunch:

roscore is a specialization of the roslaunch tool for bringing up the "core" ROS system.

And on roscore itself:

NOTE: If you use roslaunch, it will automatically start roscore if it detects that it is not already running.

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May be as an addition: It works, but can lead to strange behaviours if you start the core with a launch file, then some other launch files, you kill the first launchfile (and the core), start a new and nodes will not be able to connect anymore as they still rely on the old (vanished) roscore.

NEngelhard ( 2015-09-05 08:56:30 -0500 )edit

True, but that is always the case, even if roscore was started separately. Unfortunately ROS 1.0 is designed this way. Not sure, but this behaviour might change in ROS 2.0.

Boris ( 2015-09-05 09:31:40 -0500 )edit

But It's harder to kill a terminal with a roscore in it than relaunching a launch-file and forgetting which launch contained the master. I normally use a seperate tmux for the roscore so that I can forget it and not accidentially kill it together with some other terminals.

NEngelhard ( 2015-09-05 10:14:05 -0500 )edit

ROS 2 does not have a master anymore but works completely peer-to-peer thanks to DDS.