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Sunday, February 1, 2009

Setting up a common login across multiple wordpress installations

A pre-requisite for promoting interaction across sub-domains..

After setting up, and, i realized that the only way the parent website,, was going to get popular were through inviting user interaction on discussion boards. But for this, users would need to be logged into different sub-domains through a single login (like a global single sign-on feature of Oracle applications).


First and foremost, the version of wordpress installed on the multiple sub-domains was version 2.7. Also, the wordpress installations were done in the same database, with different table prefixes.

The table_prefix of the first wordpress installation ( was "wp_", whereas the table prefix of the other wordpress installation with which I wanted to share the userbase of, was "gita_".

Now I had to make use the same users/roles as

What worked finally..

Once you try googling it yourself, this is probably the most straightforward and common response that you would see:

In the wp-config.php of the 2nd wordpress installation, after this line:
/* That's all, stop editing! Happy blogging. */

..add the following:
define('COOKIE_DOMAIN', '');
define('COOKIEPATH', '/');
define('CUSTOM_USER_TABLE', 'wp_users');
define('CUSTOM_USER_META_TABLE', 'wp_usermeta');

But when I was going to and trying to login as admin user, I was getting you do not have " You do not have sufficient permissions to access this page." error message while using firefox browser, while IE just gave up with a page not found error.
Interestingly, this error is also encountered a log while people upgrade wordpress installations, so there is a lot of scope of mixing up resolutions while trying to solve this. Better be wary of mixing different recipes.

And so, in desperation, I searched for more options/resolutions and came across a post that suggested changing the prefix values of meta_key column in the <table_prefix>_usermeta table of the 2nd word press installation. Using this hint, I did some more tweaking by opening the phpMyAdmin interface of the gita_metadata, but the permissions error was still coming.

So, i searched a bit more and came across a posting in which a user was not able to make it work, in spite of manually the prefix of <table_prefix>_capabilities table referred in $WORDPRESS_HOME/wp-includes/capabilities.php to the table_prefix of the earlier wordpress installation (which was wp_ in my case). The change is actually quite simple: you are fixing the name of the capabilities table for a user to be wp_capabilities.
function _init_caps() {
global $wpdb;
/* $this->cap_key = $wpdb->prefix . 'capabilities'; -- the earlier entry*/
$this->cap_key = 'wp_capabilities'; /* the new entry */
$this->caps = &$this->{$this->cap_key};

And when I tried with this, not only was I able to login with the admin user's password for wordpress installation 1 in wordpress installation 2, but when I changed the URL from to, i was not redicted to a login page again, which meant that the same user was shared across different wordpress installation. (It did ask me the login once for, so perhaps the cookie was not shared really, but that is something I need to doublecheck).

Extending this concept to roles?

While going across capabilities.php, I came across a similar looking entry for user_roles and thought that logically speaking, a similar fix would be needed in capabilities.php to re-use the user roles :
function _init () {
global $wpdb;
global $wp_user_roles;
/* $this->role_key = $wpdb->prefix . 'user_roles';
$this->role_key = 'wp_user_roles';

But when I tried this, i started getting the "You do not have sufficient permissions to access this page." error again. On reverting it back like this, the login started working again:
function _init () {
global $wpdb;
global $wp_user_roles;
$this->role_key = $wpdb->prefix . 'user_roles';
/* $this->role_key = 'wp_user_roles'; */

So was it really needed..

Looking back, changing the meta_key column's entries in gita_usermeta table did not make any sense, since I was never going to use that table. To prove this point, i changed the prefix values for meta_key column back to gita_ and the admin user was still shared across nad

How to share cookies across wp installs in a common domain?

Thanks to Ben (whose comment can be seen below) for sharing the secret for making cookies work across wordpress installs in a common domain:

1) Use the same auth_salt, logged_in_salt, secret key in /wp-admin/options.php page for each sub-domain blog

2) Install Root-cookie plugin ( by LINICKX )


1. Upload root-cookie.php to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Log out
4. Log in
5. Done :o)

3) And in: wp-settings.php

Change this source code like this:

351 - define('COOKIEHASH', md5(get_option('siteurl')));


351 -  define('COOKIEHASH', md5(get_option('')));


All right, so that was a good learning on an early Sunday morning; All in 1 hour of googling and trying out options. Dont they say that early mornings are the most productive of times.


  1. Thank you for this post.... I'm making the same thing with multiple blogs and your tutorial helpt me a lot.


  2. [...] går bara att göra på Wordpress installationerna. Mer information om hur man gör detta hittar du här och [...]

  3. After upgrade to newer version for eg wordpress 2.8 to 2.9 , Will this hack work?

  4. This seems like a lot of hacking... good tutorial. but why not wrap it into a plugin then add the plugin to both installs. with the URL of the added URL?

  5. [...] Setting up a common login across multiple wordpress installations [...]

  6. And if you have the tables in differents databases ?

  7. [...] [...]

  8. This is not working in wordpress 3.0

  9. Have you had any luck with wordpress 3.0.1??

  10. Getting the "you do not have sufficient privileges" error on WP 3 after going through these steps. Any suggestions?

  11. Hi,
    thanks for posting an interesting article.Can we achieve this using Wordpress Multisite?

  12. I haven't yet been able to ever get anything that you listed above to work!

    Getting really frustrated in using WP. Creating multiple wordpress sites (in sep directories is all fine and dandy. But what USE is it if people cannot have, create, whatever, some type of login that directs users seemlessly from one blog to another? I mean REALLY! What is this????

    Given these problems, that effect more people than me, and the complexities in screwing around with the core code while not being able to find some workable soulutionn to these "very aggravating annoyances", Im afraid we're gonnan have no choice but to use some type of other CMS.

    Sad to say, but the developers of these stoooopid things ought to have known bettter.

    Very dismayed!!!!!!!!!!!!!