Linux Centos7 about man-f man and Makewhatis

After installing the CENGOS7, follow the bird Brother's book, go to a place, in the shell input man-f man Use the keyword to find more data, if not, first to create a Whatis database under root privileges.

Well, I entered Man-f man, and the result is nothing appropriate

So login root input makewhatis, result Command not found

So the pit father, Baidu for several hours without fruit. Helpless to take out Google, a search for an answer to solve the problem (suddenly seriously despise Baidu).

This does not enter Makewhatis, input mandb, problem resolution.

Linux Centos7 about man-f man and Makewhatis