WordPress Multisite (formerly WPMU) allows running multiple sites from a single WordPress installation. These constants configure and control the network.

Enabling Multisite

Step 1: Allow Multisite

define( 'WP_ALLOW_MULTISITE', true );

• Type: Boolean
• Default: Not defined (false)
• Purpose: Enables the Network Setup screen in Tools menu
• Effect: Shows "Network Setup" option in wp-admin
• Note: This just enables the setup screen, doesn’t create the network

Step 2: Run Network Setup

After adding WP_ALLOW_MULTISITE, go to:
Tools → Network Setup

WordPress will provide the additional constants to add.

Step 3: Add Network Constants

After running setup, WordPress provides these constants:

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'example.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

Core Multisite Constants

MULTISITE

define( 'MULTISITE', true );

• Type: Boolean
• Default: false
• Purpose: Indicates this is a multisite installation
• Effect: Enables all multisite functionality

SUBDOMAIN_INSTALL

define( 'SUBDOMAIN_INSTALL', true );  // Subdomain: site1.example.com
define( 'SUBDOMAIN_INSTALL', false ); // Subdirectory: example.com/site1

• Type: Boolean
• Purpose: Determines URL structure for network sites

Subdomain Mode (true)

example.com         → Main site
blog.example.com    → Site 2
shop.example.com    → Site 3

Requirements:

• Wildcard DNS: *.example.com pointing to server
• Wildcard SSL certificate (or per-subdomain certs)
• Server configured to handle wildcard subdomains

Subdirectory Mode (false)

example.com/        → Main site
example.com/blog/   → Site 2
example.com/shop/   → Site 3

Requirements:

• WordPress installed in root (not subdirectory)
• Proper permalink structure

DOMAIN_CURRENT_SITE

define( 'DOMAIN_CURRENT_SITE', 'example.com' );

• Type: String
• Purpose: Primary domain for the network
• Note: Do not include protocol or trailing slash

PATH_CURRENT_SITE

define( 'PATH_CURRENT_SITE', '/' );

• Type: String
• Purpose: Path to WordPress installation
• Value: Usually / for root installation
• Example: /blog/ if WordPress is in subdirectory

SITE_ID_CURRENT_SITE

define( 'SITE_ID_CURRENT_SITE', 1 );

• Type: Integer
• Default: 1
• Purpose: ID of the current network
• Note: Usually 1 unless running multiple networks

BLOG_ID_CURRENT_SITE

define( 'BLOG_ID_CURRENT_SITE', 1 );

• Type: Integer
• Default: 1
• Purpose: ID of the main site on the network
• Note: Main site is always ID 1

Additional Multisite Constants

SUNRISE

define( 'SUNRISE', true );

• Type: Boolean
• Default: Not defined (false)
• Purpose: Loads wp-content/sunrise.php very early in the WordPress multisite boot process
• Location: wp-content/sunrise.php (must be a drop-in at this exact path)

When SUNRISE Loads

SUNRISE loads extremely early in WordPress — after ms-settings.php runs but before:

• The current site is determined
• $current_blog is set
• Any plugins load
• Any themes load
• Most WordPress functions are available

Boot sequence with SUNRISE:

wp-load.php
  └── wp-config.php (SUNRISE defined here)
       └── wp-settings.php
            └── ms-settings.php
                 └── sunrise.php ← LOADS HERE (if SUNRISE is true)
                      └── ms-blogs.php (site determination)
                           └── plugins load
                                └── theme loads

What’s Available in sunrise.php

Available	Not Available
$wpdb (database)	$current_blog (not set yet)
$_SERVER, $_GET, $_POST	Most WordPress functions
ABSPATH, WPINC constants	get_option(), get_site_option()
Raw database queries	Hooks/filters (not loaded)
define() constants	Plugin/theme functions

Common Use Cases

1. Domain Mapping — Map custom domains to network sites
2. Early Redirects — Redirect before WordPress fully loads
3. Custom Site Routing — Override default subdomain/subdirectory logic
4. Performance — Set caching/config before anything else loads
5. Security — Block requests before WordPress processes them

sunrise.php Examples

Basic Domain Mapping:

<?php
// wp-content/sunrise.php
global $wpdb;

// Get the requested domain
$domain = strtolower( $_SERVER['HTTP_HOST'] );

// Look up mapped domain in custom table
$mapped = $wpdb->get_row( $wpdb->prepare(
    "SELECT blog_id, domain AS mapped_domain 
     FROM {$wpdb->base_prefix}domain_mapping 
     WHERE domain = %s AND active = 1",
    $domain
) );

if ( $mapped ) {
    // Force WordPress to use this site
    define( 'COOKIE_DOMAIN', $domain );
    define( 'DOMAIN_CURRENT_SITE', $domain );
    
    // Store for later use
    $GLOBALS['dm_mapped_blog_id'] = $mapped->blog_id;
}

Redirect Non-SSL to SSL:

<?php
// wp-content/sunrise.php
if ( empty( $_SERVER['HTTPS'] ) || $_SERVER['HTTPS'] === 'off' ) {
    $redirect = 'https://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
    header( 'HTTP/1.1 301 Moved Permanently' );
    header( 'Location: ' . $redirect );
    exit;
}

Block Specific Domains Early:

<?php
// wp-content/sunrise.php
$blocked_domains = array( 'spam-domain.com', 'blocked.example.com' );

if ( in_array( $_SERVER['HTTP_HOST'], $blocked_domains, true ) ) {
    header( 'HTTP/1.1 410 Gone' );
    exit( 'This site is no longer available.' );
}

Set Global Cache Group for Multisite:

<?php
// wp-content/sunrise.php
// Must run before wp_cache_add_global_groups() is called
global $wp_object_cache;

if ( function_exists( 'wp_cache_add_global_groups' ) ) {
    wp_cache_add_global_groups( array( 
        'domain_mapping',
        'global_posts',
        'site_lookups' 
    ) );
}

Language/Locale by Domain:

<?php
// wp-content/sunrise.php
$domain_locales = array(
    'example.de' => 'de_DE',
    'example.fr' => 'fr_FR',
    'example.es' => 'es_ES',
);

$host = $_SERVER['HTTP_HOST'];
if ( isset( $domain_locales[ $host ] ) ) {
    define( 'WPLANG', $domain_locales[ $host ] );
}

Creating a sunrise.php Drop-in

1. Create the file at exactly wp-content/sunrise.php
2. Add define( 'SUNRISE', true ); to wp-config.php (before ABSPATH)
3. Add your early-load logic to sunrise.php

File must:

• Be named exactly sunrise.php
• Be in wp-content/ (not a subdirectory)
• Start with <?php
• Not output anything (no echo/print before headers)

Debugging sunrise.php

Since sunrise.php runs before most debugging tools:

<?php
// wp-content/sunrise.php

// Log to file (error_log still works)
error_log( 'SUNRISE: ' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] );

// Or write to custom log
file_put_contents( 
    ABSPATH . 'wp-content/sunrise-debug.log',
    date('Y-m-d H:i:s') . ' - ' . $_SERVER['HTTP_HOST'] . "n",
    FILE_APPEND 
);

Plugins That Use SUNRISE

• WordPress MU Domain Mapping — Original domain mapping plugin
• Mercator — Modern domain mapping by Human Made
• WP Multi Network — Multiple networks support
• Cavalcade — Job queue system (early hooks)

NOBLOGREDIRECT

define( 'NOBLOGREDIRECT', 'https://example.com' );

• Type: String (URL)
• Purpose: Redirect URL for non-existent sites
• Effect: When someone accesses a subdomain/path that doesn’t exist, redirect here
• Example: notasite.example.com → redirects to https://example.com

WP_DEFAULT_THEME

define( 'WP_DEFAULT_THEME', 'twentytwentyfour' );

• Type: String
• Purpose: Default theme for new sites in the network
• Note: Also affects single-site installations

BLOG_ID_CURRENT_SITE vs get_current_blog_id()

// Constant (main site ID)
BLOG_ID_CURRENT_SITE // Always 1 (main site)

// Function (current site being viewed)
get_current_blog_id() // Returns ID of current site context

Registration Settings

ALLOW_SUBDIRECTORY_INSTALL

define( 'ALLOW_SUBDIRECTORY_INSTALL', true );

• Type: Boolean
• Default: true for fresh installs, false for upgrades
• Purpose: Allow subdirectory mode even if WordPress is not at root
• Warning: Can cause URL conflicts with existing content

User and Registration Settings

These are typically set via Network Admin, but can be overridden:

Programmatic Network Options

// In a plugin or mu-plugin
add_filter( 'site_option_registration', function() {
    return 'user'; // 'none', 'user', 'blog', 'all'
});

Cookie Configuration for Multisite

COOKIE_DOMAIN

// For subdomain installs - share cookies across subdomains
define( 'COOKIE_DOMAIN', '.example.com' );

// For subdirectory installs - usually not needed
define( 'COOKIE_DOMAIN', 'example.com' );

COOKIEPATH and SITECOOKIEPATH

define( 'COOKIEPATH', '/' );
define( 'SITECOOKIEPATH', '/' );

• Purpose: Ensure cookies work across the network

ADMIN_COOKIE_PATH

define( 'ADMIN_COOKIE_PATH', '/' );

• Purpose: Allow admin cookies to work across network sites

Network Admin Constants

Network vs Site Admin

// Check if current user is super admin
if ( is_super_admin() ) {
    // Network-level access
}

// Check if in network admin
if ( is_network_admin() ) {
    // Currently in network admin screens
}

Complete Multisite Configuration Examples

Subdomain Installation

<?php
// Database settings...

// Multisite Configuration
define( 'WP_ALLOW_MULTISITE', true );
define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', true );
define( 'DOMAIN_CURRENT_SITE', 'example.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

// Cookie settings for subdomain
define( 'COOKIE_DOMAIN', '.example.com' );
define( 'COOKIEPATH', '/' );
define( 'SITECOOKIEPATH', '/' );
define( 'ADMIN_COOKIE_PATH', '/' );

// Redirect non-existent subdomains
define( 'NOBLOGREDIRECT', 'https://example.com' );

// Security
define( 'FORCE_SSL_ADMIN', true );

// ABSPATH...

Subdirectory Installation

<?php
// Database settings...

// Multisite Configuration
define( 'WP_ALLOW_MULTISITE', true );
define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'example.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

// Redirect non-existent paths
define( 'NOBLOGREDIRECT', 'https://example.com' );

// Security
define( 'FORCE_SSL_ADMIN', true );

// ABSPATH...

WordPress in Subdirectory (Subdirectory Mode)

// WordPress installed in /cms/
define( 'WP_HOME', 'https://example.com' );
define( 'WP_SITEURL', 'https://example.com/cms' );

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'example.com' );
define( 'PATH_CURRENT_SITE', '/cms/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

Domain Mapping

For mapping custom domains to network sites:

Traditional (sunrise.php)

// wp-config.php
define( 'SUNRISE', true );

// wp-content/sunrise.php
<?php
global $wpdb;

$domain = $_SERVER['HTTP_HOST'];
$mapped = $wpdb->get_row( 
    $wpdb->prepare( 
        "SELECT blog_id FROM {$wpdb->dmtable} WHERE domain = %s", 
        $domain 
    ) 
);

if ( $mapped ) {
    define( 'COOKIE_DOMAIN', $domain );
}

Modern Plugins

Use plugins like "WordPress MU Domain Mapping" or "Mercator" for easier domain mapping.

Multisite Database Tables

Multisite adds these tables per site (where N is site ID):

Table	Purpose
wp_blogs	List of all sites
wp_blog_versions	Database version per site
wp_registration_log	Registration logs
wp_signups	Pending signups
wp_site	Network information
wp_sitemeta	Network-level options
wp_N_posts	Posts for site N
wp_N_options	Options for site N
wp_N_*	All tables duplicated per site

Troubleshooting Multisite

Common Issues

1. Cookies not working across sites

   • Check COOKIE_DOMAIN setting
   • Ensure leading dot for subdomains: .example.com

2. Redirect loops

   • Verify DOMAIN_CURRENT_SITE matches actual domain
   • Check SSL configuration

3. Can’t add new sites

   • Verify SUBDOMAIN_INSTALL matches your setup
   • Check DNS (for subdomains) or permalinks (for subdirectories)

4. 404 on subsites

   • Check .htaccess rules (provided during setup)
   • Verify server supports required rewrite rules

Required .htaccess (Apache)

Subdirectory Install:

RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*.php)$ $2 [L]
RewriteRule . index.php [L]

Subdomain Install:

RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*.php)$ $1 [L]
RewriteRule . index.php [L]

Security Considerations

1. Super Admins have full access to all sites – assign carefully
2. Plugins activated network-wide affect all sites
3. Theme availability is controlled at network level
4. File upload types can be restricted network-wide
5. Consider subdomain isolation – easier to contain compromised sites