I couldn't have managed getting SELinux work by using any of provided guides. It should be something I don't know and missing.
I was about to move on but I then discovered the most impressive feature of Linode cloud service: upload my own virtual machine! So I built a minimal (default) Centos server in my local computer, uploaded it to my Linode, changed Kernel as necessary (it is still required as I learned by experiencing), then restarted my machine, wow! It works!!!
Just in case, I made a backup as Golden master of my disk, so I wouldn't need to upload again (then I learned, I already have a Clone feature - what a beautiful place is this!).
Now I am happy! I am guessing that Centos installation in Linode doesn't include some SELinux related applications that Minimum Centos includes. So when I built and uploaded my Centos, then after changing Kernel, everything worked!
It is time to create another Linode now!

Thanks for the help!