Hello All!

I got this puzzling beginner issue. It's my first Multisite install, latest versions of all, no plugins, and when I am trying to use in a page template the switch_to_blog function, I get this :

Fatal error: Call to undefined function switch_to_blog() in /SITES/Sitename/wp-content/themes/themename/page.php on line 28

with line 28 : switch_to_blog(1);

I must do something wrong, but it looks the function itself is not installed, though the function's file is there (as it should be in any normal install).

Is there a way to cleanly create the function, declare it or activate it ? I tried copy the function switch_to_blog to functions.php, and there is does not complain but is not working (i got the article from the CURRENT blog). but then error make it stop to restore_current_blog(); with the same fatal error...

I don't know where to begin... what might help you understand the issue ? THANKS in advance.


  • It should be in wp-includes/ms-blogs.php, do you see it there?
    – Tdelang
    Oct 9, 2016 at 7:09
  • Yes there it is...
    – Gesatzs
    Oct 9, 2016 at 7:16
  • I am using MAMP 3 and 4, same result.
    – Gesatzs
    Oct 9, 2016 at 20:12
  • Please edit your question to add in the relevant code. Are you calling this in an action or a filter? If so, which one?
    – Pat J
    Oct 15, 2016 at 3:28
  • I got this error when I used switch_to_blog() inside the functions.php file of my theme, in a single site installation of WordPress 4.8.9. In a multisite installation, with the same WP version, the error did not occur! About the page.php file, I did not have any problem using that function inside it. Jan 8, 2020 at 22:59

1 Answer 1


Some time ago, but i ran into exactly the same misbehavior.

Have your multisite activated and installed correctly.

Because WordPress is just loading the functions when a multisite is really active. Here the code from wp-settings.php file around line 137 on WP 6.1.1

if ( is_multisite() ) {
    require ABSPATH . WPINC . '/class-wp-site-query.php';
    require ABSPATH . WPINC . '/class-wp-network-query.php';
    require ABSPATH . WPINC . '/ms-blogs.php'; // <--- switch_to_blog() is in here!!
    require ABSPATH . WPINC . '/ms-settings.php';
} elseif ( ! defined( 'MULTISITE' ) ) {
    define( 'MULTISITE', false );

Here i found a long read tutorial which helped me a lot: https://multilingualpress.org/docs/how-to-install-wordpress-multisite/

But there should be alternatives findable anyway.

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