The single most important feature of WordPress 3.0 is the WPMU merge which allows you to easily manage a network of sites (blogs) on a single WordPress install. You can find the instructions for enabling multisite here.

The WordPress 3.0 development cycle included over 1200 tickets (bugs and enhancements).

You can download WordPress 3.0 here and read the official release announcement on the WordPress Development Blog.

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A new Dashboard Widgets API was introduced in WordPress 2.7, which made it easy for developers to create their own widgets for the administration dashboard. Dashboard Widgets are written in PHP and it’s easy to get started if you are familiar with the WordPress Plugin API.

You can add a new widget to the dashboard using the WordPress core function wp_add_dashboard_widget( widget_id, widget_name, callback, control_callback ).

• widget_id: Unique id for your widget. This will be the css class and the array key for the widgets.
• widget_name: Name for your widget that will be displayed as the title.
• callback: The function that will display the content of the widget.
• control_callback: The function that will display the form elements and handle the form submission. This parameter is optional.

In this post, I’ll create a simple dashboard widget that will display some text:

Let’s create a function that will display the contents of our custom dashboard widget:

function devmind_dashboard_widget() {
	echo '<p><a href="http://wordpress.org/">WordPress</a> is a state-of-the-art publishing platform with a focus on aesthetics, web standards, and usability. WordPress is both free and priceless at the same time.</p>';
}

We need to create another function that will call wp_add_dashboard_widget and register our custom dashboard widget:

function devmind_add_dashboard_widget() {
	wp_add_dashboard_widget( 'devmind-custom-widget', 'About WordPress', 'devmind_dashboard_widget' );
}

Now, we need to hook into dashboard setup process and tell WordPress to load our widget. We can do this by hooking into wp_dashboard_setup and adding our custom widget.

add_action( 'wp_dashboard_setup', 'devmind_add_dashboard_widget' );

You can add this code to your theme’s functions.php file or download it as a plugin here.

WordPress checks for updates using wp_update_plugins() in wp-includes/update.php but there are no hooks in this function which could be used to exclude your plugin from the update check. However, you can hook into http_request_args and remove your plugin from the query arguments passed in the http request. You can add the following code to your plugin to prevent WordPress from checking for updates for your plugin:

add_filter( 'http_request_args', 'dm_prevent_update_check', 10, 2 );
function dm_prevent_update_check( $r, $url ) {
	if ( 0 === strpos( $url, 'http://api.wordpress.org/plugins/update-check/' ) ) {
		$my_plugin = plugin_basename( __FILE__ );
		$plugins = unserialize( $r['body']['plugins'] );
		unset( $plugins->plugins[$my_plugin] );
		unset( $plugins->active[array_search( $my_plugin, $plugins->active )] );
		$r['body']['plugins'] = serialize( $plugins );
	}
	return $r;
}

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What’s an RC? An RC comes after beta and before the final launch. It means we think we’ve got everything done: all features finished, all bugs squashed, and all potential issues addressed. But, then, with over 20 million people using WordPress with a wide variety of configurations and hosting setups, it’s entirely possible that we’ve missed something.

Download WordPress 3.0 Release Candidate 3

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WordCamp Chicago has an exciting line-up of speakers and I’m looking forward to meeting with Chicagoland WordPress people and reconnecting with some folks I met at WordCamp San Francisco. WordCamps are all about networking, so make it a plan to attend all the parties and hit me up if you see me.

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Tweak the WordPress Generator Meta Tag

The following code will remove the version number from the meta tag:

function devmnd_tweak_generator( $generator ) {
        return str_replace( ' ' . get_bloginfo( 'version' ), '', $generator );
}
add_filter( 'the_generator', 'devmnd_tweak_generator' );

Before: <meta name="generator" content="WordPress 3.0-RC1-15112" />
After: <meta name="generator" content="WordPress" />

You can even add your own custom version number in the generator meta tag:

return str_replace( get_bloginfo( 'version' ), '4.0', $generator );

Remove the WordPress Generator Meta Tag:

if ( function_exists( 'wp_generator' ) ) {
        remove_action( 'wp_head', 'wp_generator' );
}

Enable Network Menu

Add the following line to wp-config.php:

define( 'WP_ALLOW_MULTISITE', true );

The Network menu under Tools will not show up until you complete this step.

Create a Network

Log in to the WordPress back-end and navigate to the Network screen under Tools. WordPress allows you to choose between sub-domain and sub-directory based installs for your network of sites. You can choose one or the other, but it’s not easy to change later, so you must decide before you proceed.

Sub-domains:

A sub-domain install allows you to have new sites as sub-domains of your WordPress installation. For example, you can have site1.domain.com and site2.domain.com for a WordPress installation at domain.com. You will need to add a wildcard domain alias for your webserver and a wildcard DNS record for your domain. Matt has a detailed explanation about wildcard DNS records and domain alias here.

Sub-directories:

A sub-directory install allows you to have new sites as sub-directories of your WordPress installation. For example, you can have domain.com/site1 and domain.com/site2 for a WordPress installation at domain.com.

Enable Network

Create Media Directory:

Create a blogs.dir directory under wp-content for all uploaded media files for all sites in the network. You must ensure that the new directory has the correct permissions so it is writable by the web-server (apache user).

Update wp-config.php:

Add the following lines to wp-config.php anywhere above /* That’s all, stop editing! Happy blogging. */

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', true ); //false for sub-directory install
$base = '/';
define( 'DOMAIN_CURRENT_SITE', 'domain.com' ); //replace domain.com with your install
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

Update/Create .htaccess:

Create a file named .htaccess in the root WordPress directory and add the following:

Apache and sub-directory installs:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [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]

Apache and sub-domain installs:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule . index.php [L]

Replace all WordPress related .htaccess rules with the ones above if the file already exists.

Rewrite Rules for Nginx and sub-directory installs:

  #on server block
  ##necessary if using a multi-site plugin
  server_name_in_redirect off;
  ##necessary if running Nginx behind a reverse-proxy
  port_in_redirect off;

  rewrite ^.*/files/(.*)$ /wp-includes/ms-files.php?file=$1 last;
  if (!-e $request_filename) {
   rewrite ^.+?(/wp-.*) $1 last;
   rewrite ^.+?(/.*\.php)$ $1 last;
   rewrite ^ /index.php last;
  }

Return to the WordPress back-end. You will have to log-in again and now you’ll see a Super Admin menu item. You can manage your network of sites from this menu.

1. Replace WordPress Files:

Download and unzip the latest version of WordPress 3.0 (beta 2). Delete the wp-admin and wp-includes folders. Upload the unzipped files to the server, overwriting the old files. Ensure that you overwrite all the files and pay attention to the wp-content folder. You must overwrite the files in this folder and not replace the folder with the new one since it contains the themes and plugins.

2. Update WordPress:

Log in to the WordPress back-end and follow the link to the Update Network screen to update all sites(blogs) in your network.

3. Update wp-config:

WordPress encrypts cookies but you must add NONCE_SALT code shown at the top of the admin area to wp-config.php. For example: define( 'NONCE_SALT', 'a. This code will be unique to your installation. Add it above the line that says: /* That's all, stop editing! Happy blogging. */

define( "WP_USE_MULTIPLE_DB", false );

define( 'NONCE_SALT', 'a<U3S[ g<.4I)#p^-iy?sbb3JPu+W~-Zk|aPLMN[TvoiHIKGI_bbB-h?iliBb2ra' );

/* That's all, stop editing! Happy blogging. */

/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
	define('ABSPATH', dirname(__FILE__) . '/');

/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');

4. Update Rewrite Rules:

The wp-content/blogs.php file was deprecated in WordPress 3.0 and you must update the rewrite rules to use wp-includes/ms-files.php. Delete wp-content/blogs.php and change it to wp-includes/ms-files.php in .htaccess:

RewriteEngine On
RewriteBase /

#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]

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

<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>

wpmu-settings.php was also deprecated in WordPress 3.0 and can be deleted.