== <node> tag ==
<<TableOfContents(3)>>

The `<node>` tag specifies a ROS [[Nodes|node]] that you wish to have launched. This is the most common `roslaunch` tag as it supports the most important features: bringing up and taking down nodes.

`roslaunch` does not provide any guarantees about what order nodes start in. This is intentional: there is no way to externally know when a node is fully initialized, so all code that is launched must be robust to launching in any order.

The [[roslaunch/Tutorials|roslaunch tutorials page]] covers some examples of how to fully utilize the `<node>` tag, such as [[roslaunch/Tutorials/Roslaunch Nodes in Valgrind or GDB|configuring a node to launch in gdb]].

=== Examples ===
{{{
<node name="listener1" pkg="rospy_tutorials" type="listener.py" args="--test" respawn="true" />
}}}
Launches the `"listener1"` [[Nodes|node]] using the `listener.py` executable from the `rospy_tutorials` [[Packages|package]] with the command-line argument `--test`. If the node dies, it will automatically be respawned.

{{{
<node name="bar1" pkg="foo_pkg" type="bar" args="$(find baz_pkg)/resources/map.pgm" />
}}}
Launches the bar node from the `foo_pkg` package. This example uses substitution arguments to pass in a portable reference to `baz_pkg/resources/map.pgm`.

=== Attributes ===
 . `pkg="mypackage"`
  . Package of node.
 `type="nodetype"`
  . Node type. There must be a corresponding executable with the same name.
 `name="nodename"`
  . Node name. NOTE: name cannot contain a namespace. Use the `ns` attribute instead.
 `args="arg1 arg2 arg3"`''(optional)''
  . Pass arguments to node.
 `machine="machine-name"`''(optional, see [[roslaunch/XML/machine|<machine>]])''
  . Launch node on designated machine.
 `respawn="true"`''(optional, default: False)''
  . Restart the node automatically if it quits.
 `respawn_delay="30"` ''(optional, default 0)'' <<Version(ROS indigo)>>
  . If `respawn` is `true`, wait `respawn_delay` seconds after the node failure is detected before attempting  restart.
 `required="true"`''(optional)''
  . '''ROS 0.10''': If node dies, kill entire roslaunch.
 `ns="foo"`''(optional)''
  . Start the node in the 'foo' namespace.
 `clear_params="true|false"`''(optional)''
  . Delete all parameters in the node's private namespace before launch.
 `output="log|screen"`''(optional)''
  . If 'screen', stdout/stderr from the node will be sent to the screen. If 'log', the stdout/stderr output will be sent to a log file in $ROS_HOME/log, and stderr will continue to be sent to screen. The default is 'log'.
 `cwd="ROS_HOME|node"`''(optional)''
  . If 'node', the working directory of the node will be set to the same directory as the node's executable. In C Turtle, the default is 'ROS_HOME'. In Box Turtle (ROS 1.0.x), the default is 'ros-root'. The use of 'ros-root' is deprecated in C Turtle.
 `launch-prefix="prefix arguments"`''(optional)''
  . Command/arguments to prepend to node's launch arguments. This is a powerful feature that enables you to enable `gdb`, `valgrind`, `xterm`, `nice`, or other handy tools. See [[roslaunch/Tutorials/Roslaunch Nodes in Valgrind or GDB|Roslaunch Nodes in Valgrind or GDB]] for examples.
 `if="true|false"`''(optional)''
  . If 'true' the node will be launched as usual. If 'false' the node will not be launched. Can be used to evaluate arguments/parameters and run based on the outcome without modifying the launch file every time.


=== Elements ===
You can use the following XML tags inside of a `<node>` tag:

 . [[roslaunch/XML/env|<env>]]
  . Set an environment variable for the node.
 [[roslaunch/XML/remap|<remap>]]
  . Set a remapping argument for this node.
 [[roslaunch/XML/rosparam|<rosparam>]]
  . Load a [[rosparam]] file into this node's `~`/local namespace.
 [[roslaunch/XML/param|<param>]]
  . Set a [[Parameters|parameter]] in the node's `~`/local namespace.