What Exactly is WordPress MultiSite (WPMS) Install

If you’ve ever wondered what people are talking about when they mention WordPress Multisite then please read on. This brief article will explain what WordPress Multisite is, and also some of its concepts and features.

WordPress multisite, sometimes abbreviated as WPMS,  is defined in wordpress.org as:

“Multisite is a feature of WordPress 3.0 and later versions that allows multiple virtual sites to share a single WordPress installation. When the multisite feature is activated, the original WordPress site can be converted to support a network of sites.”

In other words WPMS gives you the ability to have multiple individual sites within one WordPress installation and one database which all fits under the umbrella of what is known as a network.

So when talking about WPMS it is common to refer to the whole multisite installation as the network. The term site is usually used when talking about each of the individual sites within the WPMS network.

The individual sites created within the WPMS network are also sometimes known as “virtual” sites because they don’t actually exist in the file system but only the database.

Each site within the network can feature different plugins and themes and have completely different content – just like a separate, independent single site WordPress installation.

WordPress multisite was once known as “WordPress MU” where MU stands for “multi user” and was a separate project to the main “single site” WordPress platform which we all know and love so much today.

However since 3.0, WP MU has been renamed to WPMS and is now part of the core WordPress platform.

WPMS is not enabled by default when you install WordPress and you must explicitly set a parameter in the “wp-config.php” file in order to see the WPMS menu items.

Possibly the best example of a large-scale site using WordPress multisite is wordpress.com.

This site allows people to set up their own blogs and does not require that you have a dedicated host because each individual site is hosted within the wordpress.com multisite network.

There are currently something like 30 million blogs running under the wordpress.com WPMS network and the general features available for the individual blogs are controlled by the main site administrator.

Some typcial scenarios where the multisite functionality is useful and is currently widely used, are:

• Retail stores which represent a single company and which may be located in several cities or states could each have their own dedicated site under the main WPMS  insallation. For example Best Buy uses WPMS where each store has its own WP site within the network.
• Institutions such as universities often use WPMS to represent their various departments and faculties on separate sites.
• Online news sites are another typical candidate for WP multisite. Each of the departments such as the main news, sport, finance, etc typically would have their own sites within a multisite network.
• You might be a theme developer and wish to show your customers a live demo site for each of your themes. Therefore you could create a network of live demos within WPMS.
• You might decide to set up a collection of blogs for your family and extended family, and thus WPMS might be a cool way to collectively run and maintain all of your family’s sites.

As you’ve probably already surmised, the possibilities available to you with WPMS are endless and not limited to the brief examples given above.

What are the main pros of multisite?

As you may have already guessed, multisite has some very useful advantages some of which are listed below.

• The most obvious advantage of running a multisite installation is that there is only a single installation of the WordPress platform which you need to maintain.Even though the WPMS installation may have hundreds of sites running within it, you only need to update plugins and theme versions in a single place and this will automatically apply to all of the sites.Imagine if you didn’t have multisite and you had to do separate plugin updates or installations to over a hundred single site installations – you would have to repeat each task over a hundred times!
• As an administrator of a multisite installation, you can easily set and lock down administration functionality that your network users have for things like plugins or themes. For instance you can quite easily prevent people from deactivating, upgrading or even using certain plugins or themes from within their site.
  You can also set and control disk usage per site and specify maximum file size uploads per site and even specify which filetypes are allowed to be uploaded.
• You can easily aggregate content from each of the individual sites into your main blog site within a WPMS installation. This can useful for things like showcasing content from a number of the individual sites.

What Types of URL Addresses Are Possible With Multisite?

With multisite you basically have 2 main installation types which govern how the URL addresses will appear to the outside world:

1. Sub-domains
   With this setup, each site will have a URL address which appears like the following:
   site1.example.com
   site2.example.com
   site3.example.com
   etc,
   Where example.com would be the URL of the main WordPress installation.
2. Sub-directories
   This type of setup will produce URL addresses for each site as follows:
   example.com/site1
   example.com/site2
   example.com/site3
   etc
   

For a new and fresh WordPress installation either of the above two types are easily configurable at installation time. However if you’re trying to convert an existing single site to multisite, there are certain criteria which need to be met in order to have the ability to choose the sub-directories option. (Please see the WordPress codex page for more info)

There are even plugins which make it possible to use domain mapping to produce URLs for each site which would make them appear to outside observers that the site is not part of a multisite installation.

For instance you could make the URLs for each site look like single independent sites, eg, abc.com, xyz.com, etc

Some Limitations of WPMS

Previously we mentioned that WPMS uses a single database.
Each site in a WPMS network has its own tables which contain the data for that site.

A WPMS installation has a slightly different DB schema to single sites. The tables of a site in a WPMS installation are prefixed by the table prefix followed by the blog ID followed by the table name.

For example the following shows the possible table names of two sites in a multisite install:

Due to this type of setup, it is very easy to quickly use up server resources if you tried to run a WPMS with thousands of sites on a small shared host. Therefore you would need to take such things into consideration when setting up your WPMS installation.

In summary, WPMS is a very powerful WordPress feature and one that you might want to consider.

Now that you know all about WPMS, go ahead and follow our WordPress multi-site installation tutorial to set one up 🙂