Linux info

varnish -- http://www.mormanski.net/2010/08/14/install-configure-varnish-on-ubuntu-lucid-linux
            -- http://www.lullabot.com/articles/varnish-multiple-web-servers-drupal     
varnish sticky session

LAMP -- http://txt.binnyva.com/2007/04/compile-and-install-lamp-server-from-source-php5-apache2-mysql5/
          -- http://www.devshed.com/c/a/Apache/Building-Apache-the-Way-You-Want-It/12/

linux boot process -- http://www.thegeekstuff.com/2011/02/linux-boot-process/

http://stackoverflow.com/questions/1750194/smtp-why-does-email-needs-envelope-and-what-does-the-envelope-mean

http://unixinterviewquestions.blogspot.in/2012/07/domainkeys-identified-mail-dkim.html