1：安装php7.3
sudo apt update
sudo apt-get install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt update
sudo apt install php7.3-fpm
设置PHP7.3-fpm开机启动：
Systemctl enable php7.3-fpm
2：查看php版本
Php -v
PHP 7.3.19-1+ubuntu18.04.1+deb.sury.org+1 (cli) (built: Jun 12 2020 07:48:30) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.19, Copyright (c) 1998-2018 Zend Technologies
with Zend OPcache v7.3.19-1+ubuntu18.04.1+deb.sury.org+1, Copyright (c) 1999-2018, by Zend Technologies
3：卸载PHP
sudo apt-get autoremove php7*
sudo find /etc -name "*php*" |xargs rm -rf
sudo apt purge `dpkg -l | grep php| awk '{print $2}' |tr "\n" " "`
dpkg -l | grep php7*
执行完最后一步，返回空，则卸载成功
4：安装PHP7.3插件
这里以gd库为例：
apt-get install php7.3-gd
安装完成之后，重启nginx
Systemctl restart nginx
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