title: How does Linux execute a file?
body: <p>I want to know how does Linux operating systems execute files.
  So from my searches across the web I understood that every file which has the runnable bit set on can be executed. But then I learned that there is an ELF called format which is the Linux standard for executables.</p>
  
  <p>So what I want to know is what is necessary to a file which has permission to run (runnable bit is on), in order to execute code in the system? Can I just create a new file with hex editor and write 90 inside (NOP opcode) and expect it to be executed? Or does Linux requires some kind of standard format, like ELF format or Bash format?</p>