# 10. Environment variables¶

This is the list of environment variables that affect the behavior of Fast DDS:

FASTRTPS_DEFAULT_PROFILES_FILE

Defines the location of the default profile configuration XML file. If this variable is set and its value corresponds with an existing file, Fast DDS will load its profiles. For more information about XML profiles, please refer to XML profiles.

 Linux export FASTRTPS_DEFAULT_PROFILES_FILE=/home/user/profiles.xml  Windows set FASTRTPS_DEFAULT_PROFILES_FILE=C:\profiles.xml 
ROS2_AUTO_CLIENT_SERVER

When this variable is set, it automatically activates the Server-Client Discovery. The value of the variable must represent the locator of the server, in the form of the IP address (e.g., ‘192.168.2.23’) or address-port pair (e.g., ‘192.168.2.23:24353’). If no port is specified, the default port 11311 is used.

If the specified address is a local address of the current machine, it will start the DomainParticipant as a server. If the address is a remote one, or if there is already a server at the given port, it will start the DomainParticipant as a client, connecting to the server at the specified locator.

 Linux export ROS2_AUTO_CLIENT_SERVER=192.168.2.23:24353  Windows set ROS2_AUTO_CLIENT_SERVER=192.168.2.23:24353 
FASTDDS_AUTO_CLIENT_SERVER

An alias for ROS2_AUTO_CLIENT_SERVER. If both variables are defined, only the value of ROS2_AUTO_CLIENT_SERVER is used.