untuk mengatasi error Duplicate sources.list entry saat melakukan update pada ubuntu
W: Duplicate sources.list entry http://download.virtualbox.org/virtualbox/debian/ trusty/contrib i386 Packages (/var/lib/apt/lists/download.virtualbox.org_virtualbox_debian_dists_trusty_contrib_binary-i386_Packages) W: You may want to run apt-get update to correct these problems
berikut cara mengatasinya
rm /etc/apt/sources.list.d/virtualbox.list
silahkan lakukan update kembali
apt-get update
done