@kamaln7

Didn't resolve the main issue, but did resolve some strange cookie-ing behavior (whereby, after entering username/password at example.com/wp-admin, it would redirect me to the same page; to access the example.com dashboard directly, I had to go to http://www.example.com/wp/wp-admin/).

With great pleasure. wp-config:

<?php
// ===================================================
// Load database info and local development parameters
// ===================================================
if ( fileexists( dirname( _FILE__ ) . '/local-config.php' ) ) {
define( 'WPLOCALDEV', true );
include( dirname( FILE ) . '/local-config.php' );
} else {
define( 'WPLOCALDEV', false );
define( 'DBNAME', 'example' );
define( 'DBUSER', 'will' );
define( 'DBPASSWORD', 'XXXX' );
define( 'DBHOST', 'localhost' ); // Probably 'localhost'
}

// ========================
// Custom Content Directory
// ========================
define( 'WPCONTENTDIR', dirname( FILE ) . '/content' );
define( 'WPCONTENTURL', 'http://' . $SERVER['HTTPHOST'] . '/content' );

/* Multisite */
define('WPALLOWMULTISITE', true);
define('MULTISITE', true);
define( 'DOMAINCURRENTSITE', 'example.com' );
define('SUBDOMAIN_INSTALL', true);
define( 'SUNRISE', 'on' );

// ================================================
// You almost certainly do not want to change these
// ================================================
define( 'DBCHARSET', 'utf8' );
define( 'DBCOLLATE', '' );

// ==============================================================
// Salts, for security
// Grab these from: https://api.wordpress.org/secret-key/1.1/salt
// ==============================================================
define('AUTHKEY', 'XXXX');
define('SECUREAUTHKEY', 'XXXX');
define('LOGGEDINKEY', 'XXXX');
define('NONCEKEY', 'XXXX');
define('AUTHSALT', 'XXXX');
define('SECUREAUTHSALT', 'XXXX');
define('LOGGEDINSALT', 'XXXX');
define('NONCESALT', 'XXXX');
// ==============================================================
// Table prefix
// Change this if you have multiple installs in the same database
// ==============================================================
$tableprefix = 'wrd';

// ================================
// Language
// Leave blank for American English
// ================================
define( 'WPLANG', '' );

// ===========
// Hide errors
// ===========
iniset( 'displayerrors', 0 );
define( 'WPDEBUGDISPLAY', false );

// =================================================================
// Debug mode
// Debugging? Enable these. Can also enable them in local-config.php
// =================================================================
// define( 'SAVEQUERIES', true );
// define( 'WP_DEBUG', true );

// ======================================
// Load a Memcached config if we have one
// ======================================
if ( fileexists( dirname( _FILE__ ) . '/memcached.php' ) )
$memcachedservers = include( dirname( _FILE__ ) . '/memcached.php' );

// ===========================================================================================
// This can be used to programatically set the stage when deploying (e.g. production, staging)
// ===========================================================================================
define( 'WPSTAGE', '%%WPSTAGE%%' );
define( 'STAGINGDOMAIN', '%%WPSTAGING_DOMAIN%%' ); // Does magic in WP Stack to handle staging domain rewriting

// ===================
// Bootstrap WordPress
// ===================
if ( !defined( 'ABSPATH' ) )
define( 'ABSPATH', dirname( FILE ) . '/wp/' );
require_once( ABSPATH . 'wp-settings.php' );

.htaccess:

RewriteCond %{HTTPHOST} ^example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]
RewriteCond %{HTTPHOST} ^www.foo\.com$ [NC]
RewriteRule ^(.*)$ http://foo.com/$1 [R=301,L]

Options +FollowSymlinks
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]

RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUESTFILENAME} -f [OR]
RewriteCond %{REQUESTFILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).) wp/$1 [L]
RewriteRule ^(..php)$ wp/$1 [L]
RewriteRule . index.php [L]
Require all granted

Thanks, @jtittle.

@cavaunpeu

The reference to "domain that is being mapped" would mean a physical domain such as domain01.ext, domain02.ext and so forth :-).

screenshot: http://imgur.com/Tq3QBkz

The screenshot above is of the domain setup area for the WordPress MU Domain Mapping plugin. In the Site ID input box, you'll add the ID of sub.yourdomain.ext and then in the Domain input box, this is where you'll add the domain that you want to associate with sub.yourdomain.ext. This is the actual "mapping" (from within the WordPress Admin CP).

You'll then modify the existing or add a new A entry for domain01.ext (the domain that you choose to map to sub.yourdomain.ext) that points to the IP Address that you set in the Server IP Address input box (http://imgur.com/tetUHBb).

--

Essentially, all domains that you wish to map to a sub-domain created by your WordPress MS installation need to point (by creating or modifying the existing A entry for each physical domain) to the server IP set in that screenshot.

You create the actual "mapping" inside the WordPress Admin CP and then "map" the domain name associated with the sub-domain to the server IP :-) (either through DigitalOceans CP if you use them to manage your DNS, or your domain registrar).

Does that make sense? If not, just let me know :-). Always happy to help!