Linux web application servers typically use the Linux/Apache/Mysql/PHP stack. Linux being the OS, Apache the web server layer, Mysql provides the database, and PHP the dynamic HTML/Scripting language. Their is an amazing amount of LAMP based applications out there, so getting to know how to administer a LAMP server is a key skill set for running Linux Application servers.

This first article will focus on installing the LAMP stack on an Ubuntu machine, and administering the Apache web server.

There are a few of concepts I would like to cover first though. One of them seems to escape a lot of people in this space. This is a the concept of name based virtual hosts. Name based virtual hosting is the ability for a web server to serve content based on the URL of the incoming request. This is a method of allowing a single server to serve multiple websites content without needing multiple IP addresses. Essentially the server processes the URL request by matching it against a know set of virtual host definitions. When it matches a URL to a virtual host, it serves content from the directory structure assigned to that virtual host.

The other concept is fully qualified domain names. A fully qualified domain name or FQDN is a hostname containing the host and the domain, including the top level domain suffix. Common top level domains (TLDs) are .gov, .com, .org etc. So an example of a FQDN would be: www.linuxpoweruser.com. The www is the host, and linuxpoweruser.com is the domain, so www.linuxpoweruser.com indicates the host called www in the domain linuxpoweruser.com.

The last concept is how what part of a URL is handled by the domain name system (DNS). DNS is responsible for resolving the part of a URL that is between the http:// and the next / in a URL. If there are no following /’s in a URL than DNS processes all of the URL after the http://. I am a DNS administrator for a large retailer and I am constantly asked to add an entry to add a redirect in DNS to allow, for instance, a URL called http://www.test.com to redirect to http://www.retest.com/test/test.html. Since DNS only handles the “www.test.com” or “www.retest.com” everything after the / in the destination, ie /test/test.html is not handled by DNS, and therefore DNS cannot do this sort of redirection. In this case, I can modify DNS to do a redirect for www.test.com to go to the name www.retest.com (or its corresponding server IP address) but its up to the virtual hosting definition or, a bit of redirect html code to handle the rest. Ok, enough said about that.

First, in order to install the LAMP stack on an Ubuntu system, we need to make sure we install the associated packages:

sudo apt-get install apache2 php5-mysql libapache2-mod-php5 mysql-server php5-gd phpmyadmin


There are some commands that are very useful to control Apache features and served content. The first set of commands will control the availability of Apache features. For instance, you might want to enable home directory public_html serving, which is the ability to serve content from a users public_html folder in their home directory. Content is then accessed at the web browser by going to http://server ip/~username. To do this, use the a2enmod command:

sudo a2enmod userdir && sudo /etc/init.d/apache2 restart

Other apache modules can be enabled with this a2enmod command. Here is an example that covers server side includes (we will cover server side includes in a later article):


sudo a2mod include && sudo /etc/init.d/apache2 restart


The default document root is /var/www (you need superuser privileges to write in this directory), any files in this directory that are world readable will be accessible by entering the following in a web browser:


http://server ip or name/filename


Anything in a subdirectory below /var/www will appear by appending the directory name to the url. For example, if there is a directory with content at /var/www/mywebsite, it would be accessible with the following url:

http://server/mywebsite/filename where server is the name or IP of your apache server.

New sites can be added by creating site definition files in the /etc/apache2/sites-available directory. Files in this directory are essentially apache configuration files that can be read in or included when apache starts up. This is useful for adding new websites via virtual host definitions, or enabling SSL for your sites.
Edit a new configuration file for the new site :

gksudo gedit /etc/apache2/sites-available/<filename>

Here is an example of a site definition file for adding a directory phpsysinfo as a virtual host on the server, accessible via the sysinfo.rtwsecurenet.com url.

<Directory “/var/www/phpsysinfo”>

# Possible values for the Options directive are “None”, “All”,
# or any combination of:
#   Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews
#
# Note that “MultiViews” must be named *explicitly* — “Options All”
# doesn’t give it to you.
#
# The Options directive is both complicated and important.  Please see
# http://httpd.apache.org/docs/2.2/mod/core.html#options
# for more information.

#-Indexes disables directory browsing +Includes turns on SSI

Options -Indexes FollowSymLinks +Includes

# AllowOverride controls what directives may be placed in .htaccess files.
# It can be “All”, “None”, or any combination of the keywords:
#   Options FileInfo AuthConfig Limit
AllowOverride All

# Controls who can get stuff from this server.
Order allow,deny
Allow from all

#add this to allow for different default page names

DirectoryIndex index.html index.shtml index.php

</Directory>

<VirtualHost *:80>

ServerName sysinfo.rtwsecurenet.com
DocumentRoot /var/www/phpsysinfo

</VirtualHost>

Note :80 in VirtualHost statement – needed if running combination of ssl and non-ssl sites. We will break down the components of this file later.

To enable the new site use the a2ensite command:

sudo a2ensite <sitename> && sudo /etc/init.d/apache2 restart

Later, if you would like to disable that site, you can use the a2dissite command to remove the site:

sudo a2dissite <sitename> && sudo /etc/init.d/apache2 restart

Note, that if the site content is at /var/www or a directory below it, you do not have to create a site file.  The site file is only used to include other directories other than what is below /var/www or to create virtual hosts for making content available at a specific host name.

So what is happening with this a2ensite/a2dissite commands?  Essentially, a2ensite makes symbolic links in the /etc/apache2/sites-enabled/ directory for the appropriate file/site being enabled (from the /etc/apache2/sites-available directory).  The a2dissite command simply deletes the symbolic links.

Beware of some web applications that install themselves outside of the normal /var/www and /etc/apache2/sites-available directory structures. An example comes to mind: phpmyadmin. Phpmyadmin is a php based tool for administering Mysql servers. Phpmyadmin on ubuntu does not install in the /var/www folder. Instead it installs in /usr/share/phpmyadmin. It also stores configuration in /etc/phpmyadmin. In the /etc/phpmyadmin folder there is an apache.conf file. This file is executed when Apache is started, and it includes the /usr/share/phpmyadmin directory in the web servers directory structure, so that it appears at http://servername/phpmyadmin, as if it was a directory under /var/www. How does it do this? Another directory, /etc/apache2/conf.d includes symlinks to files to be included in the apache configuration. Its actually very similar to sites-enabled/available. In /etc/apache2/conf.d/ there is a phpmyadmin.conf that is symlinked to /etc/phpmyadmin/apache.conf. These symlinks are created by apt during package installation.

So, in short we have covered installing the LAMP stack, and controlling Apache’s configuration for serving content. In the next article, we will cover creating Secure Sockets Layer (SSL) websites using apache.