roslaunch

roslaunch is a tool in the Robot Operating System (ROS) that starts and configures multiple ROS nodes as a single operation, using declarative launch files. A launch file is an XML document that describes a set of nodes, parameters, topic remappings, and other resources required to run an application. By orchestrating the startup and shutdown of many nodes, roslaunch provides a reproducible and modular way to deploy ROS-based systems.

Launch files contain elements such as node, param, remap, arg, include, group, and machine. The node element specifies the package, executable, node name, and options such as output and respawn. The param element sets values on the ROS parameter server. The remap element rewrites topic or service names. The include element allows composing larger configurations from smaller ones, and group enables scoping and remappings for namespaces. The machine element enables launching nodes on remote machines over SSH, supporting distributed systems.

Typical usage is roslaunch package name.launch or roslaunch package file.launch. roslaunch will start roscore if it is not already running, set up the parameter server, apply remappings and arguments, and start the requested nodes. Output can be directed to the screen or to log files; logs are stored under ~/.ros/log for later inspection. It also supports features such as automatic restart of failed nodes, and orderly startup ordering via dependencies or grouping.

roslaunch is part of ROS 1 and remains a core tool for coordinating complex systems, especially in simulations, robot platforms, and multi-robot setups. It emphasizes repeatability, modularity, and centralized management of runtime configuration.