Step 1: Setting up virtual host for main network domain
WordPress doesn’t allow to install the sub-domain multisite for local WordPress installation. So, first thing we need to is to set up the virtual host for main network site.

For the demonstration purpose, i am assuming “http://localhost/your-site” as the main local WordPress installation where you want to install multisite with sub-domains and i will map this local site to virtual domain “http://your-site.com”.

To set up the virtual hosts, use following two commands

#1
sudo gedit /etc/hosts
and then add following line of code
127.0.0.1       your-site.com

#2
sudo gedit sudo gedit /etc/apache2/sites-enabled/000-default.conf
and then add following lines of code
#For sub-domain your-site.com
<VirtualHost *:80>
    DocumentRoot /var/www/html/your-site/
    ServerName your-site.com

    <Directory /var/www/html/your-site>
        Options +Indexes +FollowSymlinks +MultiViews +Includes
        AllowOverride FIleInfo Options
        Order allow,deny
        allow  from all
    </Directory>
</VirtualHost>

Now, we are done with setting up virtual host for main domain.

Step 2: Setting up virtual hosts for other sub-domains

sudo gedit /etc/hosts 
and then add following lines of code
127.0.0.1       site1.your-site.com


sudo gedit /etc/apache2/sites-enabled/000-default.conf

<VirtualHost *:80>
    DocumentRoot /var/www/html/your-site/
    ServerName site1.your-site.com

    <Directory /var/www/html/your-site>
        Options +Indexes +FollowSymlinks +MultiViews +Includes
        AllowOverride FIleInfo Options
        Order allow,deny
        allow  from all
    </Directory>
</VirtualHost>

Note: The document root and directory should point to the local folder of main domain.

Now, you can add as many as subdomains by followig the above procedures. If you are comfortable, you can set up multiple virtual hosts at the same time.

You will need to restart the apache2 server.

sudo systemctl restart apache2

Step 3: Installing WP Multisite
Open wp-config.php file and add following code:

define('WP_ALLOW_MULTISITE', TRUE);

Then, reload the WP backend and you will see the “Network setup” submenu under “Tools”.
The next step is to click the “Network Setup” and you will be redirected to network set up page as shown in following image.

Choose the “Sub-domains” and click “install”.
As a final step, you will be instructed to put some codes in “wp-config.php” file and “.htaccess” file.

Note: Make sure to keep backups of both files in case needed to revert back.

All Done. !!!!!!!!

P.S. if you are on windows or mac, please find a way to set up virtual hosts. Rest of the processes are same.

Original Post: Installation of multisite with sub-domains on localhost