Function and usage of ms_subdomain_constants() in wordpress


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    The ms_subdomain_constants() function in WordPress is specifically designed for use in a Multisite network environment. Here's a detailed explanation of its function and usage:


    • Name: ms_subdomain_constants()
    • Purpose: This function is responsible for defining constants related to Multisite subdomain installations and managing associated warnings and notices.

    Description and Usage:

    1. Subdomain vs Subdirectory: WordPress Multisite can be set up in one of two ways: using subdomains (e.g., or subdirectories (e.g., The ms_subdomain_constants() function is pivotal in handling the subdomain setup.

    2. VHOST Deprecation: Previously, the constant VHOST was used to determine whether a Multisite network was using subdomains or subdirectories. However, VHOST has been deprecated in favor of SUBDOMAIN_INSTALL.

    3. SUBDOMAIN_INSTALL Constant:

      • Type: Boolean
      • Purpose: It indicates whether the Multisite network is configured for subdomains (true) or subdirectories (false).
      • Setting Up: This constant is typically defined in wp-config.php during the setup of a Multisite network.
    4. Function Behavior:

      • First Call: During its first invocation, the function checks and defines the necessary constants based on the network's configuration. This step is crucial for setting up the network correctly.
      • Second Call: On subsequent calls, the function operates with the advantage of having translations loaded, allowing it to trigger warnings and notices more effectively. This is especially useful for alerting administrators to any misconfigurations or deprecated settings.
    5. Warnings and Notices: The function is capable of generating warnings, particularly related to the deprecated VHOST constant. It ensures that site administrators are aware of the current best practices for Multisite configurations.

    Sample Usage:

    In a typical scenario, a WordPress developer or administrator does not need to directly invoke ms_subdomain_constants(). This function is internally used by WordPress during the setup and management of a Multisite network. However, understanding its role is important for troubleshooting and ensuring proper Multisite configuration.

    • In wp-config.php, you might see a line like:
      define('SUBDOMAIN_INSTALL', true); // For subdomain setup
    • This line indicates that the network uses a subdomain configuration, and ms_subdomain_constants() would use this constant to define network behavior accordingly.


    The ms_subdomain_constants() function is an integral part of setting up and managing a WordPress Multisite network, specifically for subdomain configurations. Its primary role is to define the necessary constants and provide warnings for deprecated or incorrect configurations, thereby ensuring the network operates smoothly.

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