Fatal error: Call to undefined function wp_installing()

2 comments

1. Here’s what helped me to fix the problem:

   1) create a backup of all files and the database (highly suggest)

   2) Delete all files and folders except for the folder wp-content. You will need this folder. It contains all the files for your theme and plugin.

   3) Replace all the wordpress files in the install download EXCEPT for wp-content.

   4) Update wp-config.php with your database credentials. They can be retrieved in your current wp-config.php.

   5) Test your website. If all seems well login into your admin panel and see if the database needs updated.

   Hope it helps, if you didn’t already solve the problem.

2. The function wp_installing is a new function in /wp-includes/load.php, as of WordPress v4.4.0.

   From my research/experience, there are 2 reasons for the problem (and it could be both):

   1) Corrupted WordPress files, for example caused by an incomplete update installation, in which case you need to reupload (eg. via FTP) the core WordPress files (ie. /wp-admin/, /wp-includes/, and the .php files in the root of your WordPress site (although be careful with wp-config.php if you have a dev environment version too!)). At the very least check that /wp-includes/load.php includes the new function definition for function wp_installing().

   2) WordPress becomes “confused” by an update installation (for example by a failed update), thinking that it is in the installation process, when it is not (or when it failed partway).

   After making sure that 1) was not the problem (by doing a file comparison between the ‘out of the box’ WordPress files (from the WordPress zip download), doing a bit more research, and pulling my hair out), I found that there is a WordPress PHP flag WP_INSTALLING that the core uses during an update as part of handling the installation process. At my wits end I temporarily put the following in wp-config.php:

   define('WP_INSTALLING', false);
   

   and reloaded my failed/broken site, and lo and behold, my WordPress site started working! I then remove this line, and the site has been working fine since.

   I can only assume that because my first attempt to update WordPress using the automatic WordPress update feature failed, and that when I then FTP’d up all the WordPress core files in attempt to do a manual update to fix it, that WordPress was somehow confused as to what state it was in (which even restarting the web server didn’t fix). Forcing the WP_INSTALLING flag temporarily to false thus got WordPress sorted out internally, and allowed things to operate normally again. Interestingly after doing this, WordPress prompted me to update my database (which I did), and which seems to me to confirm that the WordPress update installation got interrupted midway and was the cause of my problems/this fatal error/WordPress thinking that the WP_INSTALLING flag was actually currently set as true.

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