Check in wp-config.php which folder is assigned as the temporary directory. the line will start with
define('WP_TEMP_DIR', ABSPATH . '/path/to/temp');
Through ftp check the permission on the folder. It should be 755.
Even if all seems alright the update might still failed. In my case my wp-config.php is placed outside the public directory altogether. I decided to go with a temp folder also place outside of the public directoy, those I had to modify my wp-config.php (which is placed in its dedicated directory) as follow:
. I decided to go with a temp folder also place outside of the public directoy, those I had to modify my wp-config.php (which is placed in its dedicated directory) as follow:
define('WP_TEMP_DIR', ABSPATH . '/../temp/');
The path that was causing the error was as follow:
define('WP_TEMP_DIR',dirname(FILE).'/wp-content/uploads');
Placing the wp-config.php outside the public directory allow for an extra layer of security in case the php settings of the apache server get messed up and the php files are exposed instead of being executed. Even though this situation SHOULD NOT happen, there is a possibility that it does and that’s what security is about afterall: being prepared for the unlikely events.