If you are using Ubuntu, you can use these commands to install PHP 8:

Enable neccessery repository:

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

Once the PPA is enabled, you can install PHP 8

Now, there are some small differences if you are using Apache or Nginx:

Apache
Installing PHP as an Apache module is a straightforward task:

sudo apt update
sudo apt install php8.0 libapache2-mod-php8.0
sudo apt install php8.0-fpm libapache2-mod-fcgid
sudo a2enmod proxy_fcgi setenvif
sudo a2enconf php8.0-fpm

Once the packages are installed, restart Apache for the PHP module to get loaded:

sudo systemctl restart apache2

Nginx

sudo apt update
sudo apt install php8.0-fpm

Once the installation is completed, the FPM service will start automatically. To check the status of the service, run

systemctl status php8.0-fpm

Install PHP extensions
Extensions are available as packages and can be easily installed with apt :

sudo apt install php8.0-[extenionName]

Here is a list of the most common extenions you’ll need:

sudo apt install -y php8.0-mysql php8.0-dom php8.0-simplexml php8.0-ssh2 php8.0-xml php8.0-xmlreader php8.0-curl  php8.0-exif  php8.0-ftp php8.0-gd  php8.0-iconv php8.0-imagick php8.0-json  php8.0-mbstring php8.0-posix php8.0-sockets php8.0-tokenizer

Having said that it’s good to have these extensions as well.

sudo apt install -y php8.0-mysqli php8.0-pdo  php8.0-sqlite3 php8.0-ctype php8.0-fileinfo php8.0-zip php8.0-exif

That’s it, you now have PHP8.