1. Go to ubuntu software center, and install dropbox.
  2. Now clicking on dropbox icon will keep asking for authentication. To resolve this, do following :
  3. If you are behind proxy, and for some reason, can't download things from terminal, then previous command will give error, because it can't download a file www.dropbox.com/download?plat=lnx.x86_64
  4. Download that file manually from browser by typing www.dropbox.com/download?plat=lnx.x86_64 in address bar, and saving file.
  5. Extract that file and move that to home directory.
  6. Now run dropbox by typing dropbox start -i. It will start
  7. If you are behind proxy, you have to set proxy settings by going into preferences, which comes by right clicking on dropbox icon created on top of desktop. Once you set proxy settings, it will enter into setup process. Note that, it may happen that during setup, it resets proxy and thus loses connection. Then you have to again set the proxy.