Before You Create A Network « WordPress Codex: "This guide describes how to install manually WordPress Multisite in your current WordPress installation. There are also available ready-to-run packages from BitNami.
Types of multisite network
You can choose between several different types of multisite network depending on how you want your network to handle URLs, and on whether it will allow end users to create new sites on demand.
Different types of network have different server requirements, which are described in a section below. If you do not have full control over your server then certain types of multisite network might not be available to you. For example, you might not have full control over your server because you use a shared hosting environment. In that case you will have to negotiate the requirements with whoever operates the hosting environment."
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