All modules PHP 5.6

Install PHP 5.6 On linux (Debian, Ubuntu, Mint ...)

sudo apt-get install python-software-properties
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
sudo apt-get install -y php5.6

heck Installed PHP Version

php -v

 
Install PHP 5.6 Modules

Show available PHP Modules list
sudo apt-cache search php5.6-* 
Install modules which is required for you.
Example PHP 5.6:
sudo apt-get install libapache2-mod-php5.6 php5.6-cgi php5.6-cli php5.6-curl php5.6-imap php5.6-gd php5.6-mysql php5.6-pgsql php5.6-sqlite3 php5.6-mbstring php5.6-json php5.6-bz2 php5.6-mcrypt php5.6-xmlrpc php5.6-gmp php5.6-xsl php5.6-soap php5.6-xml php5.6-zip php5.6-dba

Example PHP 7:
sudo apt-get install libapache2-mod-php7.0 php7.0-common php7.0-mysql php7.0-curl php7.0-json php7.0-cgi php7.0-gd

 

PHP 5.6 Modules list (Example)

php-amqp - AMQP extension for PHP
php-apcu - APC User Cache for PHP
php-geoip - GeoIP module for PHP
php-igbinary - igbinary PHP serializer
php-imagick - Provides a wrapper to the ImageMagick library
php-mongodb - MongoDB driver for PHP
php-msgpack - PHP extension for interfacing with MessagePack
php-oauth - OAuth 1.0 consumer and provider extension
php-redis - PHP extension for interfacing with Redis
php-rrd - PHP bindings to rrd tool system
php-smbclient - PHP wrapper for libsmbclient
php-solr - PHP extension for communicating with Apache Solr server
php-ssh2 - Bindings for the libssh2 library
php-uuid - PHP UUID extension
php-yac - YAC (Yet Another Cache) for PHP
php-zmq - ZeroMQ messaging bindings for PHP
php-radius - radius client library for PHP
php-http - PECL HTTP module for PHP Extended HTTP Support
php-uploadprogress - file upload progress tracking extension for PHP
libapache2-mod-php5.6 - server-side, HTML-embedded scripting language (Apache 2 module)
php5.6-cgi - server-side, HTML-embedded scripting language (CGI binary)
php5.6-cli - command-line interpreter for the PHP scripting language
php5.6-phpdbg - server-side, HTML-embedded scripting language (PHPDBG binary)
php5.6-fpm - server-side, HTML-embedded scripting language (FPM-CGI binary)
libphp5.6-embed - HTML-embedded scripting language (Embedded SAPI library)
php5.6-dev - Files for PHP5.6 module development
php5.6-common - documentation, examples and common module for PHP
php5.6 - server-side, HTML-embedded scripting language (metapackage)
php5.6-curl - CURL module for PHP
php5.6-gd - GD module for PHP
php5.6-imap - IMAP module for PHP
php5.6-intl - Internationalisation module for PHP
php5.6-ldap - LDAP module for PHP
php5.6-mysql - MySQL module for PHP
php5.6-pgsql - PostgreSQL module for PHP
php5.6-pspell - pspell module for PHP
php5.6-recode - recode module for PHP
php5.6-snmp - SNMP module for PHP
php5.6-sqlite3 - SQLite3 module for PHP
php5.6-sybase - Sybase module for PHP
php5.6-tidy - tidy module for PHP
php5.6-opcache - Zend OpCache module for PHP
php-xdebug - Xdebug Module for PHP
php5.6-json - JSON module for PHP
php-memcached - memcached extension module for PHP, uses libmemcached
php5.6-bz2 - bzip2 module for PHP
php5.6-mcrypt - libmcrypt module for PHP
php5.6-odbc - ODBC module for PHP
php5.6-readline - readline module for PHP
php5.6-interbase - Interbase module for PHP
php5.6-xmlrpc - XMLRPC-EPI module for PHP
php5.6-enchant - Enchant module for PHP
php5.6-gmp - GMP module for PHP
php5.6-xsl - XSL module for PHP (dummy)
php-memcache - memcache extension module for PHP
php-gmagick - Provides a wrapper to the GraphicsMagick library
php5.6-bcmath - Bcmath module for PHP
php5.6-mbstring - MBSTRING module for PHP
php5.6-soap - SOAP module for PHP
php5.6-xml - DOM, SimpleXML, WDDX, XML, and XSL module for PHP
php5.6-zip - Zip module for PHP
php-tideways - Tideways PHP Profiler Extension
php-mailparse - Email message manipulation for PHP
php-propro - propro module for PHP
php-raphf - raphf module for PHP
php-stomp - Streaming Text Oriented Messaging Protocol (STOMP) client module for PHP
php-gearman - PHP wrapper to libgearman
php-xcache - fast, stable PHP opcode cacher
php-mongo - MongoDB database driver
php5.6-dba - DBA module for PHP
php-xhprof - Hierarchical Profiler for PHP 5.x

ref: https://www.drupal8.ovh/en/tutoriels/178/how-to-install-php-on-linux