Source

File: wp-admin/includes/schema.php

function populate_network_meta( $network_id, array $meta = array() ) {
	global $wpdb, $wp_db_version;

	$network_id = (int) $network_id;

	$email             = ! empty( $meta['admin_email'] ) ? $meta['admin_email'] : '';
	$subdomain_install = isset( $meta['subdomain_install'] ) ? (int) $meta['subdomain_install'] : 0;

	// If a user with the provided email does not exist, default to the current user as the new network admin.
	$site_user = ! empty( $email ) ? get_user_by( 'email', $email ) : false;
	if ( false === $site_user ) {
		$site_user = wp_get_current_user();
	}

	if ( empty( $email ) ) {
		$email = $site_user->user_email;
	}

	$template       = get_option( 'template' );
	$stylesheet     = get_option( 'stylesheet' );
	$allowed_themes = array( $stylesheet => true );

	if ( $template != $stylesheet ) {
		$allowed_themes[ $template ] = true;
	}

	if ( WP_DEFAULT_THEME != $stylesheet && WP_DEFAULT_THEME != $template ) {
		$allowed_themes[ WP_DEFAULT_THEME ] = true;
	}

	// If WP_DEFAULT_THEME doesn't exist, also include the latest core default theme.
	if ( ! wp_get_theme( WP_DEFAULT_THEME )->exists() ) {
		$core_default = WP_Theme::get_core_default_theme();
		if ( $core_default ) {
			$allowed_themes[ $core_default->get_stylesheet() ] = true;
		}
	}

	if ( function_exists( 'clean_network_cache' ) ) {
		clean_network_cache( $network_id );
	} else {
		wp_cache_delete( $network_id, 'networks' );
	}

	wp_cache_delete( 'networks_have_paths', 'site-options' );

	if ( ! is_multisite() ) {
		$site_admins = array( $site_user->user_login );
		$users       = get_users(
			array(
				'fields' => array( 'user_login' ),
				'role'   => 'administrator',
			)
		);
		if ( $users ) {
			foreach ( $users as $user ) {
				$site_admins[] = $user->user_login;
			}

			$site_admins = array_unique( $site_admins );
		}
	} else {
		$site_admins = get_site_option( 'site_admins' );
	}

	/* translators: Do not translate USERNAME, SITE_NAME, BLOG_URL, PASSWORD: those are placeholders. */
	$welcome_email = __(
		'Howdy USERNAME,

Your new SITE_NAME site has been successfully set up at:
BLOG_URL

You can log in to the administrator account with the following information:

Username: USERNAME
Password: PASSWORD
Log in here: BLOG_URLwp-login.php

We hope you enjoy your new site. Thanks!

--The Team @ SITE_NAME'
	);

	$misc_exts        = array(
		// Images.
		'jpg',
		'jpeg',
		'png',
		'gif',
		// Video.
		'mov',
		'avi',
		'mpg',
		'3gp',
		'3g2',
		// "audio".
		'midi',
		'mid',
		// Miscellaneous.
		'pdf',
		'doc',
		'ppt',
		'odt',
		'pptx',
		'docx',
		'pps',
		'ppsx',
		'xls',
		'xlsx',
		'key',
	);
	$audio_exts       = wp_get_audio_extensions();
	$video_exts       = wp_get_video_extensions();
	$upload_filetypes = array_unique( array_merge( $misc_exts, $audio_exts, $video_exts ) );

	$sitemeta = array(
		'site_name'                   => __( 'My Network' ),
		'admin_email'                 => $email,
		'admin_user_id'               => $site_user->ID,
		'registration'                => 'none',
		'upload_filetypes'            => implode( ' ', $upload_filetypes ),
		'blog_upload_space'           => 100,
		'fileupload_maxk'             => 1500,
		'site_admins'                 => $site_admins,
		'allowedthemes'               => $allowed_themes,
		'illegal_names'               => array( 'www', 'web', 'root', 'admin', 'main', 'invite', 'administrator', 'files' ),
		'wpmu_upgrade_site'           => $wp_db_version,
		'welcome_email'               => $welcome_email,
		/* translators: %s: Site link. */
		'first_post'                  => __( 'Welcome to %s. This is your first post. Edit or delete it, then start writing!' ),
		// @todo - Network admins should have a method of editing the network siteurl (used for cookie hash).
		'siteurl'                     => get_option( 'siteurl' ) . '/',
		'add_new_users'               => '0',
		'upload_space_check_disabled' => is_multisite() ? get_site_option( 'upload_space_check_disabled' ) : '1',
		'subdomain_install'           => $subdomain_install,
		'global_terms_enabled'        => global_terms_enabled() ? '1' : '0',
		'ms_files_rewriting'          => is_multisite() ? get_site_option( 'ms_files_rewriting' ) : '0',
		'initial_db_version'          => get_option( 'initial_db_version' ),
		'active_sitewide_plugins'     => array(),
		'WPLANG'                      => get_locale(),
	);
	if ( ! $subdomain_install ) {
		$sitemeta['illegal_names'][] = 'blog';
	}

	$sitemeta = wp_parse_args( $meta, $sitemeta );

	/**
	 * Filters meta for a network on creation.
	 *
	 * @since 3.7.0
	 *
	 * @param array $sitemeta   Associative array of network meta keys and values to be inserted.
	 * @param int   $network_id ID of network to populate.
	 */
	$sitemeta = apply_filters( 'populate_network_meta', $sitemeta, $network_id );

	$insert = '';
	foreach ( $sitemeta as $meta_key => $meta_value ) {
		if ( is_array( $meta_value ) ) {
			$meta_value = serialize( $meta_value );
		}
		if ( ! empty( $insert ) ) {
			$insert .= ', ';
		}
		$insert .= $wpdb->prepare( '( %d, %s, %s)', $network_id, $meta_key, $meta_value );
	}
	$wpdb->query( "INSERT INTO $wpdb->sitemeta ( site_id, meta_key, meta_value ) VALUES " . $insert ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
}