don't use sudo!

01-install-contiki.org

@@ -255,7 +255,10 @@ vagrant reload
 - You now need to login on the VirtualBox window that comes up after the reboot. The username should be =vagrant= with the password =vagrant=.
 
 - To get X running, you can just run =startx= on the command line after logging in on the gui window.
-Note: at this stage, some people end up using +sudo startx+, which (a) is not needed and (b) means that everything then has to run under the root user. If you have a problem with permissions at this stage, read the messages carefully and try to resolve the specific problems.
+Note: at this stage, some people end up using +sudo startx+ (WARNING! DO NOT DO THIS!), which (a) is not needed and (b) means that everything then has to run under the root user. If you have a problem with permissions at this stage, read the messages carefully and try to resolve the specific problems. To resolve (ONLY IF YOU NEED TO) use the following find command
+#+BEGIN_SRC sh
+sudo find . -user root -exec chown vagrant:vagrant {} \;
+#+END_SRC
 
 * Step 8 make sure you have all the submodules  
 - You may need to download the cooja submodules if you haven't already