NameVirtualHost

The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows NT. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.

Apache httpd has been the most popular web server on the Internet since April 1996, and celebrated its 17th birthday as a project this February

I have just restarted apache2, an error message displays on terminal:

Virtual Host *:80 --mixing * ports and non-* ports with a NameVirtualHost address is not supported, proceeding with undefined results

Well, I thought: “Is it another challenge to overcame? Yes, it is!”. I have found tips and could figured out to solve it.
All you need is modify a file called virtual.conf and add ‘:80’ after ‘*’. Then you ought to restart web server and you won’t see an error message anymore.

In the file /etc/apache2/conf.d/virtual.conf, it should be like as:

<NameVirtualHost *:80>
 ServerName localhost
 DocumentRoot /var/www/
</NameVirtualHost>

Virtual Box Guest Additions

Virtual Box Guest Additions is software provided by Oracle Sun Virtual Box that improves virtual machine’s features.

Lately I have installed Debian 7 (Wheezy) on my virtual machine. But the virtual machine has not configured correctly yet because it hasn’t installed graphics card. To have a graphics card installed on my virtual machine, I have had to follow all those steps:

  1. Must be an administrator, type su and then insert my password;
  2. Type uname -r to check the version number I need;
  3. Type apt-get install dkms build-generic linux-headers-version number. When it has installed with success, I shut down my virtual machine.
  4. I have to enable the 3D acceleration as showed in the next picture.
    3D Acceleration - Display Settings
    3D Acceleration – Display Settings

If you have followed all those steps, you would have enjoyed Gnome3. Thanks to solution #1 and solution #2, I have solved the problem.

Keys

That’s a lot of keys to try remember! The following list briefly summarizes the different flavors:

  • Compound key or composite key:A key that includes more than one field.
  • Superkey:A set of columns for which no two rows can have the exact same values.
  • Candidate key:A minimal key
  • Unique key:A superkey used to require uniqueness by the database
  • Primary key:A unique key that is used to quickly locate records by the database
  • Alternate key:A candidate key that is not the primary key.
  • Secondary key:A key used to look up records but that may not guarantee uniqueness.

One last kind of key is the foreign key. A foreign key is used as a constraint rather than to find records in a table, so it is described a bit later in the section “Constraints”

Sthephens,R. (2009), Introduction to Databases and Database Design, Beginning Database Design Solutions (pp. 52-54)