Configuring a basic multi-site development environment in Linux

This page describes the minimum required steps for configuring a multi-site development environment on a Linux machine. The steps go through how to set up two development sites with the names testsite and testsite2. By replacing these names with ones of your choice, you can set up your personalized multi-site testing environment in Linux. The sites will share the same Drupal installation, but will use different databases. These instructions assume that you have the necessary system requirements for Drupal and know how to use a Linux command prompt.

Step 1: Download and uncompress Drupal

It is not recommended to install Drupal through your package manager, as the available Drupal package is usually outdated. You can download and uncompress Drupal by following the steps on the Download and uncompress Drupal page of the Installation guide, as this step does not differ from a normal installation.

Step 2: Set up your hosts file

Add the following lines to /etc/hosts:

127.0.0.1    testsite.localhost
127.0.0.1    testsite2.localhost

Step 3: Set up Virtual Hosts

Add the following code to /etc/apache2/httpd.conf:

<VirtualHost *:80>
   DocumentRoot /var/www/html
   ServerName localhost
</VirtualHost>
<VirtualHost *:80>
    DocumentRoot /var/www/drupal
    ServerName testsite.localhost
</VirtualHost>
<VirtualHost *:80>
    DocumentRoot /var/www/drupal
    ServerName testsite2.localhost
</VirtualHost>

The stanza (paragraph) about /var/www/html is there to preserve the possibility to put non-Drupal sites in that directory. If you want only Drupal sites to be served, you can ignore it. You should also change the directory /var/www/drupal to the location you uncompressed Drupal in step 1.
After this, restart Apache:
sudo /etc/init.d/apache2 restart

Step 4: Set up your databases

Create two databases using the instructions found on the Create the database page of the Installation guide. Name one of them testsite and the other testsite2.

Step 5: Set up your sites folders

1. From the command prompt, navigate to /var/www/drupal/sites/ or wherever you have your sites folder installed.
2. Copy the default.settings.php to testsite.localhost/settings.php and testsite2.localhost/settings.php

The resulting directory structure should contain a folder for each domain name (like testsite.localhost or yourdomain.com) with a settings.php file in each folder.

For Drupal 8: Activate the multi-site feature by copying (and renaming) the file sites/example.sites.php to sites/sites.php. There is no need to edit the file unless you need site aliases.
For Drupal7: There is no need for sites.php file unless you need site aliasing feature. The normal site selection rules applies. 

Step 6: Configure your sites to use the appropriate databases

1. In the /var/www/drupal/sites/testsite.localhost/ directory, edit the settings.php file as follows (assuming you are using MySQL):
   

   $databases = array (
     'default' =>
     array (
       'default' =>
       array (
         'database' => 'testsite', 
         'username' => 'testuser', 
         'password' => 'password', 
         'host' => 'localhost', 
         'port' => '', 
         'driver' => 'mysql', 
         'prefix' => '', 
       ), 
     ), 
   );

2. Repeat for /var/www/drupal/sites/testsite2.localhost/, except replace testsite with testsite2.

Step 7: Run the installation script for your sites

In a web browser, visit http://testsite.localhost/install.php and follow the instructions found on the Run the installation script page of the Installation guide. Repeat for http://testsite2.localhost/install.php.

Step 8: Remove write permissions from your sites' settings.php files

You don't really need to do this, since this is only a development environment, so we're not really concerned about security. Nevertheless, it's a good habit to get into:
From the command prompt, navigate to /var/www/drupal/sitesand remove the write permissions for the settings.php files:
sudo chmod a-w testsite.localhost/settings.php
sudo chmod a-w testsite2.localhost/settings.php

Step 9: You're done!

You can visit your sites at:
http://testsite.localhost/index.php
http://testsite2.localhost/index.php

Other resources

Local multi-site installation of Drupal 7 on Linux