5.4. Who am I?
5.4.1. whoami
Yes, there really are occasions when you will want to ask whoami?
If you use su or use different names on different
machines, you may not remember your username at a given time. whoami
prints your effective user ID (UID), which is the one that
determines your permissions to do operations on files and run programs.
Therefore, if you log on as yourself and su to root, whoami
will report root.
5.4.2. id
A more flexible command for printing user information is id(1).
id gives more detailed output than whoami,
writing your numerical user ID as well as your name, plus your group
ID and name. Not all Unixes have whoami, so you will sometimes
need to use id instead.