Troubleshooting: Running tomcat7 at Eclipse Juno in Ubuntu

The most famous error you will meet is 'Cannot create a server using the selected type'. The only solution works for me is from [link]. But some people cannot found these files to delete:
cd ~/workspace/.metadata/.plugins/org.eclipse.core.runtime/.settings/
rm org.eclipse.jst.server.tomcat.core.prefs
rm org.eclipse.wst.server.core.prefs
The reason is that you go to the wrong workspace: here "~/workspace" means your current Eclipse workspace but no your home directory. Under your home directory, it also exists 
Quite confuse ha!