The difference between displaying the process ps aux and ps -ef under Linux

The command ps to display the system process under Linux, the most commonly used are ps -ef and ps aux (please do not use ps -aux) What is the difference between these two?

Not much difference, to discuss this issue, it goes back to two styles in Unix systems, System V style and BSD style, ps aux was originally used in Unix Style, and ps -ef was used in System V Style, both The output is slightly different. Most Linux systems today can use both methods at the same time.