How to install oci8 instant client for Ubuntu Linux

• First prerequirements are a working apache2 and php7.2 (Ubunti 18.04) environment.
• Download the basic (like instantclient-basic-linux.x64-12.2.0.1.0.zip) and the sdk (instantclient-sdk-linux.x64-12.2.0.1.0.zip) package from the Oracle Website http://www.oracle.com/technetwork/database/database-technologies/instant-client/downloads/index.html
• Upload both files to your webserver, you can use WinSCP (windows) or rsync/scp (linux) for it
• Unzip both files on server, in my case, you will get a new folder named "instantclient_12_2"
• Create destination folder : mkdir /opt/oracle
• Move and rename the instantclient folder: mv instantclient_12_2 /opt/oracle/instantclient
• Change rights on folder: chown -R root:www-data /opt/oracle 
• Check if you have the required packages for installing OCI8: apt install php7.2-dev php-pear build-essential libaio1 
• Create necessary soft links: ln -s /opt/oracle/instantclient/libclntsh.so.12.1 /opt/oracle/instantclient/libclntsh.so; ln -s /opt/oracle/instantclient/libocci.so.12.1 /opt/oracle/instantclient/libocci.so
• Add instant client to ld config files : echo /opt/oracle/instantclient > /etc/ld.so.conf.d/oracle-instantclient.conf
• Update Dynamic Linker Run-Time Bindings : ldconfig
• Now install OCI8 by pecl: pecl install oci8 
• The OCI8 installation is asking you for the right folder: instantclient,/opt/oracle/instantclient
• Add oci lib to the cli php config (console php): echo "extension = oci8.so" >>/etc/php/7.2/cli/php.ini
• Add oci lib to the apache php config: echo "extension = oci8.so" >> /etc/php/7.2/apache2/php.ini
• Set environment variables for the cli version (you will need to reboot the server after): echo "LD_LIBRARY_PATH=\"/opt/oracle/instantclient\"" >> /etc/environment echo "ORACLE_HOME=\"/opt/oracle/instantclient\"" >> /etc/environment
• Set environement variables for the apache version: echo "export LD_LIBRARY_PATH=\"/opt/oracle/instantclient\"" >> /etc/apache2/envvars; echo "export ORACLE_HOME=\"/opt/oracle/instantclient\"" >> /etc/apache2/envvars 
• Restart Apache: service apache2 restart or systemctl restart apache2 
• You're done, now you can test your connection to the Oracle database

Update: If you're using Ubuntu 22.04 LTS with php 8.1, then then pecl install oci8-3.2.1

Original source: https://serverfault.com/questions/911475/howto-install-oracle-oci8-instantclient-on-ubuntu-18-04