Go to the following link to download you copy of Nessus.
http://www.tenable.com/products/nessus/select-your-operating-system
For 32-bit :
wget "http://downloads.nessus.org/nessus3dl.php?file=Nessus-5.2.1-ubuntu1110_i386.deb&licence_accept=yes&t=8bd3179e2669137382555cb07611a795&__utma=96148739.876193166.1369081770.1369081770.1369084100.2&__utmb=96148739.3.10.1369084100&__utmc=96148739&__utmx=-&__utmz=96148739.1369084100.2.2.utmcsr=google|utmccn=(organic)|utmcmd=organic|utmctr=(not%20provided)&__utmv=-&__utmk=236900745" -O Nessus-5.2.1-ubuntu1110_i386.deb
For 64-bit :
wget "http://downloads.nessus.org/nessus3dl.php?file=Nessus-5.2.1-ubuntu1110_amd64.deb&licence_accept=yes&t=8bd3179e2669137382555cb07611a795&__utma=96148739.876193166.1369081770.1369081770.1369084100.2&__utmb=96148739.3.10.1369084100&__utmc=96148739&__utmx=-&__utmz=96148739.1369084100.2.2.utmcsr=google|utmccn=(organic)|utmcmd=organic|utmctr=(not%20provided)&__utmv=-&__utmk=236900745" -O Nessus-5.2.1-ubuntu1110_amd64.deb
Step 2 :
sudo dpkg -i Nessus-5.2.1-ubuntu1110_i386.deb
or
sudo dpkg -i Nessus-5.2.1-ubuntu1110_adm64.deb
Go to the following link to register your Nessus Plugin feed :
http://www.tenable.com/products/nessus/nessus-homefeed
sudo /etc/init.d/nessusd start
Point your Firefox to :
https://localhost:8834/
Follow the instructions on the browser.
Activate your Nessus plugin feed via the received email.
After that, you should disable the nessusd from being loaded automatically when bootup.
sudo update-rc.d nessusd disable
Step 3 :
To run it.
sudo /etc/init.d/nessusd start
Point your Firefox to :
https://localhost:8834/
That's all! See you.