How to fix/suppress "apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1." warning message?

Warning message Before the fix:

"apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message"


Fix: 
execute the following command in terminal

echo "ServerName localhost" | sudo tee -a /etc/apache2/apache2.conf

Now restart apache server by executing the following command

sudo /etc/init.d/apache2 restart


Message after the fix:
[ ok ] Restarting web server: apache2.

How to resolve "no suitable module for running kernel found" error in virtualbox instalation in debian linux?

1. Check wheather you machine is installed with "linux-headers-, linux-image-"
by issueing the follwing command in terminal.

  $dpkg -l | grep linux

In my case my kernel version is "3.16.0-4-686-pae" so the output of the above command would be something like as follows, 

Missing linux headers package

If you don't find any linux-headers or linux-images then you must install them first.

2. To find the your kernel version use the following command
  $uname -a

[ My output -> Linux hostname 3.16.0-4-686-pae #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) i686 GNU/Linux ]

now install the required packages specified in step 1.

3.  Uninstall your previous virutalbox package and reinstall it.

  $sudo apt-get remove --purge virtualbox
  $sudo apt-get instlal virtualbox

4.  Restart you machine.