Mr. Ugo Cupcic suggested that i should run sudo chmod 777 /dev/rtc And then i should be able to access the /dev/rtc as normal user. What he suggested regarding changing permissions worked but i still get segmentation faults.The program stops after the client and the server are initialized.They never start communicating. the following is the output i get currently: UINodeRepository::Scan() Scanning def /usr/lib/flowdesigner/toolbox done loading def files loading XML document from memory done! Building network  :MAIN ROS node : HARK_MASTER_NODE generated... node_RosAddHarkIntClient_1 constructor end... node_RosAddHarkIntClient_1 initialized... node_RosAddHarkIntServer_1 initialized... ROS initialized... Segmentation fault ________________________________ From: Ashwin Kamath To: Ros Mailing list Sent: Wednesday, 8 June 2011 11:29 AM Subject: Error while running a simple server client program in flowdesigner i am trying to run the following tutorial:http://winnie.kuis. kyoto-u.ac.jp/HARK/wiki.cgi? page=HARK-ROS+Tutorial+2 but i get the following error and the program stops abruptly:  [ INFO] [1307457046.525074887]: Connected to master at [localhost:11311]  ROS node : HARK_MASTER_NODE generated...  /dev/rtc: Permission denied  Cannot open /dev/rtc  ioctl: Bad file descriptor  node_RosAddHarkIntClient_1 constructor end...  node_RosAddHarkIntClient_1 initialized...  node_RosAddHarkIntServer_1 initialized...  ROS initialized...  Segmentation fault  since i was having issues with permissions i tried using sudo and ran the file in terminal,but i get the following error;  ROS_ROOT is not set!  Using default rosconsole configuration values  UINodeRepository::Scan()  Scanning def /usr/lib/flowdesigner/toolbox  done loading def files  loading XML document from memory  done!  Building network  :MAIN  [FATAL] [1307457375.864763327]: ROS_MASTER_URI is not defined in the environment. Either type the following or (preferrably) add this to your ~/.bashrc file in order set up your local machine as a ROS master:  export ROS_MASTER_URI=http:// localhost:11311 then, type 'roscore' in another shell to actually launch the master program.  [FATAL] [1307457375.864837707]: BREAKPOINT HIT          file = /tmp/buildd/ros-cturtle-ros-1. 2.6/debian/ros-cturtle-ros/ opt/ros/cturtle/ros/core/ roscpp/src/libros/master.cpp          line=70  Trace/breakpoint trap  i exported the ROS_MASTER_URI variable in the .bashrc file and started roscore in a new terminal.but the result is same.i still get the same error.Can some one please tell me how to resolve this issue.