Ubuntu 16.04默认安装php7.0环境，但是php7目前兼容性并不是很好，如果自行安装php5需要清除php7的已安装包，否则会报错。
移除默认及已安装的PHP包
sudo dpkg -l | grep php| awk '{print $2}' |tr "\n" " "
sudo apt-get install aptitude
sudo aptitude purge `dpkg -l | grep php| awk '{print $2}' |tr "\n" " "`
【另外的方法】
sudo apt-get --purge remove php7.0*
(或者 sudo apt-get --purge remove php5* libapache2-mod-php5)
sudo apt-get autoremove php7.0*(php5)
添加 PPA
sudo add-apt-repository ppa:ondrej/php
安装php5.6
sudo apt-get update
sudo apt-get install php5.6
安装扩展
sudo apt-get install php5.6-gd
sudo apt-get install php5.6-mysql
安装Apache2
sudo apt install apache2
sudo apt-get install libapache2-mod-php5.6
安装MySQL
sudo apt install mysql-server php5.6-mysql root root0x0
sudo apt-get install mysql-client
mysql_secure_installation
安 phpmyadmin
sudo apt-get install phpmyadmin
sudo apt-get install php5.6-mbstring
sudo apt-get install php5.6-gettext
sudo ln -s /usr/share/phpmyadmin /var/www/html/phpmyadmin
配置phpmyadmin
nano /etc/php/5.6/apache2/php.ini
display_errors = On(显示错误日志，出现两次，都要改，不然无效)
extension=php_mbstring.dll (开启mbstring)
sudo dpkg-reconfigure phpmyadmin (重新配置phpmyadmin)
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