Installing/Configuring
PHP Manual

Requirements

To connect to IBM DB2 Universal Database for Linux, UNIX, and Windows, or IBM Cloudscape, or Apache Derby, you must install an IBM DB2 Universal Database client on the same computer on which you are running PHP. The extension has been developed and tested with DB2 Version 8.2.

To connect to IBM DB2 Universal Database for z/OS or iSeries, you also require IBM DB2 Connect or the equivalent DRDA gateway software.

Requirements on Linux or Unix

The user invoking the PHP executable or SAPI must specify the DB2 instance before accessing these functions. You can set the name of the DB2 instance in php.ini using the ibm_db2.instance_name configuration option, or you can source the DB2 instance profile before invoking the PHP executable.

If you created a DB2 instance named db2inst1 in /home/db2inst1/, for example, you can add the following line to php.ini: 

ibm_db2.instance_name=db2inst1
If you do not set this option in php.ini, you must issue the following command to modify your environment variables to enable access to DB2: 
bash$ source /home/db2inst1/sqllib/db2profile
To enable your PHP-enabled Web server to access these functions, you must either set the ibm_db2.instance_name configuration option in php.ini, or source the DB2 instance environment in your Web server start script (typically /etc/init.d/httpd or /etc/init.d/apache).