Differences between WHO, whoami and who am I

First, let's take a look at the different results of the three commands entered by common users and root users:

 

The difference is that whoami displays the User Name of the current "Operation user", while who am I displays the User Name of the "Login User.

The Linux term is as follows: (actual user = uid, that is, user ID. Valid user = EUID, I .e. valid user ID)

 

Who am I displays the actual user name, that is, the user ID when the user logs on. This command is equivalent to WHO-M.
Whoami displays a valid user ID (Operation user).