Installing and Configuring PHP

Introduction

Client-side programming languages, like JavaScript, are handled by the browser. Major browsers like Firefox, Chrome, Safari, Edge, etc. all include JavaScript engines that use just-in-time compilers to execute the JavaScript code (Mozilla has a nice description of the process.) From an end user's perspective, you basically install JavaScript when you install a web browser.

PHP, on the other hand, is a server-side programming language, which means it must be installed on the server in order to be used. From a system or web administrator's perspective, this means that not only does PHP have be installed on a server, but it must also be configured to work with the HTTP server, which in our case is Apache2.

The main use of PHP is to interact with databases, like MySQL, MariaDB, PostgreSQL, etc., in order to create dynamic page content. This is our goal in the last part of this class. To accomplish this, we have to:

Install PHP and relevant Apache2 modules
Configure PHP and relevant modules to work with Apache2
Configure PHP and relevant modules to work with MariaDB

Install PHP

As normal, we will use apt install to install PHP and relevant modules and then restart Apache2 using the systemctl command:

sudo apt install php libapache2-mod-php
sudo systemctl restart apache2

We can check its status and see if there are any errors:

systemctl status apache2

Check Install

To check that it's been installed and that it's working with Apache2, we can create a small PHP file in our web document root. To do that, we change to the /var/www/html/ directory, and create a file called info.php:

cd /var/www/html/
sudo nano info.php

In that file, add the following text, then save and close the file:

<?php
phpinfo();
?>

No visit that file using the external IP address for your server. For example, in Firefox, Chrome, etc, go to (be sure to replace the IP below with your IP address):

http://55.333.55.333/info.php

You should see a page that provides system information about PHP, Apache2, and the server. The top of the page should look like Figure 1 below:

Fig. 1. A screenshot of the title of the PHP install page.

Basic Configurations

By default, when Apache2 serves a web page, it looks for and servers a file titled index.html, even if it does not display that file in the URL bar. Thus, http://example.com/ actually resolves to http://example.com/index.html in such cases.

However, if our plan is to provide for PHP, we want Apache2 to default to a file titled index.php instead and to the index.html file as backup. To configure that, we need to edit the dir.conf file in the /etc/apache2/mods-enabled/ directory. In that file there is a line that starts with DirectoryIndex. The first file in that line is index.html, and then there are a series of other files that Apache2 will look for in the order listed. If any of those files exist in the document root, then Apache2 will serve those before proceeding to the next. We simply want to put index.php first and let index.html be second on that line.

cd /etc/apache2/mods-enabled/
sudo nano dir.conf

And change the line to this:

DirectoryIndex index.php index.html index.cgi index.pl index.xhtml index.htm

Whenever we make a configuration change, we can use the apachectl command to check our configuration:

apachectl configtest

If we get an Syntax Ok message, you can reload the Apache2 configuration and restart the service:

sudo systemctl reload apache2
sudo systemctl restart apache2

Now create a basic PHP page. cd back to the document root directory and use nano to create and open and index.php file:

cd /var/www/html/
sudo nano index.php

Creating an index.php File

Let's now create an index.php page, and add some HTML and PHP to it. The PHP can be a simple browser detector. Change to the /var/www/html/ directory, and use sudo nano to create and edit index.php. Then add the following code:

<html>
<head>
<title>Broswer Detector</title>
</head>
<body>
<p>You are using the following browser to view this site:</p>

<?php
echo $_SERVER['HTTP_USER_AGENT'] . "\n\n";

$browser = get_browser(null, true);
print_r($browser);
?>
</body>
</html>

Next, save the file and exit nano. In your browser, visit your external IP address site:

http://55.333.55.333/

Although your index.html file still exists in your document root, Apache2 now returns the index.php file instead. However, if for some reason the index.php was deleted, then Apache2 would revert to the index.html file since that's what's next in the dir.conf DirectoryIndex line.

Conclusion

In this section, we installed PHP and configured it work with Apache2. We also created a simple PHP test page that reported our browser user agent information on our website.

In the next section, we'll learn how to complete the LAMP stack by adding the MariaDB relational database to our setup.

Linux Systems Administration