Trying to enable oom_killer

You just need a memory leak in some long running process. Here is a minimal example you can try for yourself, if you want to see how OOM looks like:

Code
/*****************************************************************************
 * leak.cpp                                                                  *
 *                                                                           *
 * This program creates a nasty memory leak that is likely to crash any Linux*
 * computer. Comes with NO WARRANTY. Use at your own risk.                   *
 *                                                                           *
 * To compile, run:                                                          *
 * g++ leak.cpp -o leak                                                      *
 *****************************************************************************/ 
int main() {
  while (true) {
    long double* p = new long double[1000];
  }
}

If you’re going to execute this, it would be a good idea to have the Magic SysRq Key enabled, because you’re going to need to reboot somehow.