Please fill in the following information:

Issue description: In RH199 for RHEL9, in ch7s06 it says "Because the command does not return any errors, it confirms that the configuration settings are correct." This is misleading, because it gives the impression that Unix commands only have errors when they print out a message. This is absolutely not true. The Unix convention is to return a zero status for success, and a non-zero status for an non-success (including errors). Non-success/errors do not necessarily print a message, but they do return non-zero. See 'grep' for examples of this. The text could add the "echo $?" command to check the return value, and say "Since the command returned zero, and it does not print any errors, we know the command was successful."  

Steps to reproduce:

Expected result: