Enable or Disable Automatic Updates of WordPress Core, Themes and Updates using Functions.php

Placing this in functions.php will enable automatic updates of the WordPress core, plugins and themes.

/* configure automatic updates */

add_filter( 'auto_update_core', '__return_true' );

add_filter( 'auto_update_plugin', '__return_true' );

add_filter( 'auto_update_theme', '__return_true' );

Changing

__return_true

to

__return_false

disables said updates.

These can be further refined to limit the level of updates and include only certain plugins.

Details to be found here:

https://codex.wordpress.org/Configuring_Automatic_Background_Updates