卸载php8后导致php7.4不能被apache解析了

今天突然发现web页面不能解析了，直接返回php代码了，想起来可能是由于不小心更新过apt 源，有一次安装了php8，后来又卸载，导致的，查了一下，发现是libapache2-mod-php没安装。

我就 sudo apt-get install libapache2-mod-php 直接执行安装了，结果发现又把php8安装上来了，大意了，现在源最新的php是8，然后又 sudo apt remove php8 系列相关，然后重新search

$ sudo apt search libapache2-mod-php7.4
Sorting... Done
Full Text Search... Done
libapache2-mod-php7.4/focal,now 7.4.23-1+ubuntu20.04.1+deb.sury.org+1 amd64 [residual-config]
  server-side, HTML-embedded scripting language (Apache 2 module)

php7.4-fpm/focal,now 7.4.23-1+ubuntu20.04.1+deb.sury.org+1 amd64 [installed]
  server-side, HTML-embedded scripting language (FPM-CGI binary)

然后就 sudo apt-get install libapache2-mod-php7.4 跑一下

$ sudo apt-get install libapache2-mod-php7.4
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  libapache2-mod-php7.4
0 upgraded, 1 newly installed, 0 to remove and 17 not upgraded.
Need to get 0 B/1,371 kB of archives.
After this operation, 4,680 kB of additional disk space will be used.
Selecting previously unselected package libapache2-mod-php7.4.
(Reading database ... 241958 files and directories currently installed.)
Preparing to unpack .../libapache2-mod-php7.4_7.4.23-1+ubuntu20.04.1+deb.sury.org+1_amd64.deb ...
Unpacking libapache2-mod-php7.4 (7.4.23-1+ubuntu20.04.1+deb.sury.org+1) ...
Setting up libapache2-mod-php7.4 (7.4.23-1+ubuntu20.04.1+deb.sury.org+1) ...
apache2_invoke: Enable module php7.4
Processing triggers for libapache2-mod-php7.4 (7.4.23-1+ubuntu20.04.1+deb.sury.org+1) ...

执行完毕重启apache，好了，代码按7.4解析了