Upgrading Apache2 Php 7.4 FPM to 8.1 PHP FPM

Install php 8.1

Add the necessary repository.

$ sudo apt install software-properties-common
$ sudo add-apt-repository ppa:ondrej/php
$ sudo apt update

Install PHP 8.

$ sudo apt install php8.1

Install Modules

Install related PHP modules

Here are some common ones

 sudo apt install php8.1-common php8.1-fpm php8.1-mysql  php8.1-xml php8.1-xmlrpc php8.1-curl php8.1-mbstring php8.1-gd  php8.1-opcache php8.1-readline php8.1-zip php8.1-intl php8.1-cli php8.1-apcu

but you can check what you have installed and need to replace by running this command

list installed php modules

$ dpkg -l | grep php7.4

Set up FPM config files

a2enmod proxy_fcgi setenvif
a2enconf php8.1-fpm

Copy any custom pools modifications to your new pool directory

cp custom.conf /etc/php/8.1/fpm/pool.d

in the new directory /php/8.1/fpm/pool.d

find and replace any references to old php version

nano domain.conf

then start or restart the service

systemctl start php8.1-fpm.service

Edit any and all apache host files you wish to run on the new version

cd /etc/apache2/sites-available

nano domain.com.conf

replace old php version with new version

 <FilesMatch \.php$>
        # Apache 2.4.10+ can proxy to unix socket
        SetHandler "proxy:unix:/run/php/php8.1-fpm-username.sock|fcgi://localhost/"
#SetHandler "proxy:fcgi://127.0.0.1:9000"
 </FilesMatch>

Restart the Apache web server.

$ sudo systemctl restart apache2.service