卸载旧版本
#删除php的相关包及配置
sudo apt-get autoremove php7*
#清除dept列表
sudo apt purge `dpkg -l | grep php| awk '{print $2}' |tr "\n" " "`
#检查是否卸载干净（无返回就是卸载完成）
dpkg -l | grep php7*安装php7.4
sudo apt install php8.1
sudo apt install php8.1-fpm
sudo apt install php8.1-mysql
sudo apt install php8.1-mbstring
sudo apt install php8.1-xml
sudo apt install php8.1-curl
sudo apt install php8.1-gd
sudo apt install php8.1-bcmath
sudo apt install php8.1-imagick
sudo apt install php8.1-zip
sudo apt install php8.1-intl