ubantu php7.0版本降级到php5.6

我本机是ubuntu16.10, Lamp环境，亲测有效

要想切换版本，首先你得安装php5.6和7.0;执行如下指令：　　

sudo add-apt-repository ppa:ondrej/php

sudo apt-get update

sudo apt-get install php7.0 php5.6 php5.6-mysql php-gettext php5.6-mbstring php-xdebug libapache2-mod-php5.6 libapache2-mod-php7.0

切换 PHP 版本 ( Apache )指令:

• from php5.6 to php7.0:
  sudo a2dismod php5.6 ; sudo a2enmod php7.0 ; sudo service apache2 restart

• from php7.0 to php5.6:
  sudo a2dismod php7.0 ; sudo a2enmod php5.6 ; sudo service apache2 restart

参考地址：http://askubuntu.com/questions/756879/cant-install-php5-on-ubuntu-16-04