There is a problem with laravel5.4 under the ubuntu16.04 system. How to change the default php version in apache2 back to 5.6?

Question

As the title says, I want to use laravel to develop a system. After some testing, I found that there is a problem with the default php7.0 of ubuntu16.04, so I want to switch back to 5.6. It keeps happening, how to solve it?
If there is an expert who knows how to make laravel5.4 run perfectly without changing the PHP version, please feel free to enlighten me.
Thanks in advance!

This error is reported: (after checking through composer event command)
PHP Fatal error: Uncaught Error: Call to undefined function ComposerConsolejson_decode() in /usr/share/php/Composer/Console/Application.php:145

Answer 1

I said that I have no problem at all in 7.0 and 7.1 environments

Answer 2

Is there any problem? Is there any error report? ! No problem found in laravel5.4 in php7.0

Answer 3

It should be that there is no json module in php

apt-get install php7.0-json

Answer 4

Switching the php version is very simple. You only need to kill the running php process first, and then start your php5 process. It should be noted that to start php5, you need to use the installation directory method to start, find the bin directory under the php5 installation directory, and then execute php