Lets install Nessus in Ubuntu in a few steps 
Open a terminal window and type in:
sudo apt-get install nessus
sudo apt-get install nessusd
sudo nessus-adduser
then add a user to nessus, set user and passwd, to login when ready.
sudo ln -fs /etc/init.d/nessusd /etc/rc2.d/S20nessusd
sudo /etc/init.d/nessusd start
sudo gedit /usr/share/applications/Nessus.desktop
Insert the following lines into the new file
[Desktop Entry]
Name=Nessus
Comment=Nessus
Exec=nessus
Icon=/usr/share/pixmaps/nessus.xpm
Terminal=false
Type=Application
Categories=Application;System;
After that you can find Nessus in the Gnome menu under Applications -> System Tools.
