Ok, first of all, I deleted wp-admin and wp-includes folders and created new ones as symbolic links. Though the frontend worked well, I couldn’t log in into admin area, because the browser was redirected to that blog which was the base for all the rest for unknown reason.

The investigation shown, that admin area of WordPress is a separate sub-application, thing in itself, and in my case it resolves the absolute path to its source as the path to the base blog. I wanted each blog to use its own folder because there are config file and uploads folder.

It took me some time to find a solution. It requires two steps.

First, I added this line to the top of the .htaccess to make any PHP request to the blog (the blog front-end and the admin area scripts) call the same script before thier start:

#fix for several sites on the same WP installation
php_value auto_prepend_file "/var/www/site_doc_root/prepend.php"

In this code /var/www/ is the root folder for all my sites, and the site_doc_root is the document root of the current site (folder where all its files are located).

OK, the 2nd step — the contents of the prepend.php script. It is easy — it just must define an absolute path constant which is used all around the WordPress:

<?php
define('ABSPATH', dirname(__FILE__).'/');

OK, after that I decided not to use one of the blogs as source for others, but download a fresh copy of WordPress and make it a source of the symbolic links for all my blogs. This helps to update them.

Then I deleted wp-admin and wp-includes folders and some wp-files and recreated them as symlinks. Attention to wp-config.php — don’t delete it, keep it unique for every site!

To make this task easier, I created setup.sh file, pasted the contents I show below, run this command

chmod 755 setup.sh

then I copied it in every site folder and launched there for every site:

ln -s /var/www/wordpress/wp-admin wp-admin
ln -s /var/www/wordpress/wp-includes wp-includes

ln -s /var/www/wordpress/wp-app.php wp-app.php
ln -s /var/www/wordpress/wp-atom.php wp-atom.php
ln -s /var/www/wordpress/wp-blog-header.php wp-blog-header.php
ln -s /var/www/wordpress/wp-comments-post.php wp-comments-post.php
ln -s /var/www/wordpress/wp-commentsrss2.php wp-commentsrss2.php
ln -s /var/www/wordpress/wp-config-sample.php wp-config-sample.php
ln -s /var/www/wordpress/wp-cron.php wp-cron.php
ln -s /var/www/wordpress/wp-feed.php wp-feed.php
ln -s /var/www/wordpress/wp-links-opml.php wp-links-opml.php
ln -s /var/www/wordpress/wp-load.php wp-load.php
ln -s /var/www/wordpress/wp-login.php wp-login.php
ln -s /var/www/wordpress/wp-mail.php wp-mail.php
ln -s /var/www/wordpress/wp-pass.php wp-pass.php
ln -s /var/www/wordpress/wp-rdf.php wp-rdf.php
ln -s /var/www/wordpress/wp-register.php wp-register.php
ln -s /var/www/wordpress/wp-rss.php wp-rss.php
ln -s /var/www/wordpress/wp-rss2.php wp-rss2.php
ln -s /var/www/wordpress/wp-settings.php wp-settings.php
ln -s /var/www/wordpress/wp-trackback.php wp-trackback.php
ln -s /var/www/wordpress/xmlrpc.php xmlrpc.php

That’s not all

I decided to update my WordPress installation every one or two months.

To do that, in the /var/www/ folder (where all my sites reside) let’s create an update script update_wordpress.sh with the following contents:

wget --timestamping http://wordpress.org/latest.zip
unzip -o latest.zip

This will download a fresh copy of the wordpress if it’s changed (though wordpress team doesn’t show the file Last-Modified header, I think one day they will) and unzip it to /var/www/wordpress/ folder which is the source for our symlinks.

Yes, you got it right — launching this script is all I need to update all my blogs.

Let’s make it periodic:

crontab -e

and then add this line to run the update process automatically every 1st day of every month at 9 AM:

0 9 1 * * /var/www/update_wordpress.sh > mail -s "WordPress updated" your@email.com

P.S. Of course, SVN checkout can be used for that purpose