One or both of the following scenarios applies.
Problem scenario #1
Try to install kubectl, but you get an error message about it being installed.
Problem scenario #2
You run "man kubectl" but you see no man page. You still think kubectl is installed.
What should you do?
Solution
Run this command: kubectl version
The results should give you some clues as to what is wrong. You may want to see this posting if you are using a Red Hat derivative or this posting for any distribution of Linux.