Install Symfony 3 with MongoDB

Install Composer

sudo apt install php php7.0-xml php7.0-intl php7.0-dev php7.0-zip phpunit php-xml
php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
php -r "if (hash_file('SHA384','composer-setup.php') ==='669656bab3166a7aff8a7506b8cb2d1c292f042046c5a994c43155c0be6190fa0355160742ab2e1c88d40d5be660b410') {echo'Installer verified';} else {echo'Installer corrupt'; unlink('composer-setup.php');} echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"
sudo mv composer.phar /usr/local/bin/composer

Install Symfony

sudo mkdir -p /usr/local/bin
sudo curl -LsS https://symfony.com/installer -o /usr/local/bin/symfony
sudo chmod a+x /usr/local/bin/symfony

Install MongoDB

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 0C49F3730359A14518585931BC711F9BA15703C6
echo "deb [arch=amd64,arm64] http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.4.list
sudo apt update
sudo apt install mongodb-org
sudo systemctl start mongod

Install the MongoDB PHP Driver with PECL

sudo apt install libssl-dev pkg-config php-pear
sudo apt install php-pear
sudo pecl install mongodb

add the following line to your php.ini file

# /etc/php/7.0/cli/php.ini
extension=mongodb.so

create your Symfony project than enter to it

composer create-project symfony/framework-standard-edition YOUR_PROJECT_NAME
cd YOUR_PROJECT_NAME

Install the MongoDB adapter

composer require alcaeus/mongo-php-adapter

Install MongoDB Doctrine packages

composer require doctrine/mongodb-odm doctrine/mongodb-odm-bundle