Repository Setup
In order to do even minimal changes to a standard postgresql deploy (like install postGIS) you must be sure you have control of where you get your packages. This is not as straight forward as it should be. I encourage you to take a few minutes to read this through. First, your "disto repository" is not likely to be up to date with respect to postgresql packages. In other words, if If you blindly type "yum install postgresql-devel", you may have trouble getting everything installed properly. I've seen errors regarding missing libraries and the like. To avoid the fuss, when you are installing postgresql packages, use the
Use the postgresql repositories instead of your ditsro repsositorythe Centos repsositories.
Here is how you do that.
Understanding this now will save you lots of time (in other words you really should read this from top to bottom).
Also read this; you can safley skip sections on this page.