by Matthew Spurrier.
What Ken means is that he doesn't run Ubuntu, however he's found a possible answer for you.
In order to use php5-json you also may need to enable the plugin prior to being able to use it in PHP.
You'll see in /etc/php5 there's a mods-available folder, with all the installed mods, however you won't see this in conf.d
You need to copy the .ini file from mods-available to the conf.d folder in order to activate that PHP module, you then
need to restart Apache (and/or php-fpm).
Hope that helps
Matt