1. Installing Informix Client SDK for Linux x86_64

  1.1 Download Informix Client SDK 3.70 for Linux x86_64 from IBM website, https://www-01.ibm.com/marketing/iwm/tnd/search.jsp?rs=ifxdl
  
  1.2 Extract the file, `cd /opt/informix; tar -xvf clientsdk.3.70.FC8DE.LINUX.tar`
  
  1.3 Start installation, `./installclientsdk`
  
2. Installing PDO Informix

  2.1 Download PDO Informix 1.3.1, `wget https://pecl.php.net/get/PDO_INFORMIX-1.3.1.tgz`
  
  2.2 Extract the file, `tar -xvf PDO_INFORMIX-1.3.1.tgz`
  
  2.3 `cd PDO_INFORMIX-1.3.1` and compiling
  
    2.3.1 `phpize`, if getting error `configure: error: Cannot find php_pdo_driver.h`, do `ln -s /usr/include/php5 /usr/include/php` and try again.
    
    2.3.2 `make`
    
    2.3.3 `make install`
    
3. Include pdo_informix.so in php.ini