Originally Posted by mlangdn
It could possibly point to an unsupported cpu.
While that is theoretically possible, that is usually too literal an interpretation of the Illegal instruction error.
It is not that easy to get Centos installed on a system with an unsupported CPU.
There is far too little information in the original post to make a useful guess about the problem, maybe too little to even ask constructive questions to get the info necessary to guess the real problem.
What kind of a system is it (basic hardware info)? How did it get to its current condition (fresh install of Centos; upgrade from a previous version; sudden behavior change in a previously working system, or what)?
That still won't be enough to enable a good guess at the problem, so hopefully the OP knows a bit more about what is unusual in the way the system reached its current condition to offer more relevant info.