open a terminal and do:
sudo -s apt-get install build-essential subversion ruby libruby irb rdoc libyaml-ruby libzlib-ruby libopenssl-ruby libdl-ruby libreadline-ruby libiconv-ruby rubygems sqlite3 libsqlite3-ruby libsqlite3-dev ruby1.9.1-dev libpcap-dev svn co https://www.metasploit.com/svn/framework3/trunk/ metasploit cd metasploit svn up cd external/pcaprub sudo ruby extconf.rb && make && make install msfconsole