8.3 Identifying Users
8.3.3 User account information
The login id that you use to initially login to a UNIX system is your Real User ID (RUID). While logged in, you can switch to another user's id and become them for a period of time in order to modify files they own or do something on their behalf. You will have all the same characteristics and permissions of the account you switched to and this is now your Effective User ID (EUID).

Figure shows three commands that can be used to help determine your identity when working with different user accounts, who am i, whoami and id. The who am i command shows your Real User ID (RUID). The id and whoami commands show your effective User ID (EUID). The id command can also be used with the -a (all) option to show all groups the effective user is a member of.

Interactive Media Activity (Flash, 95 kB)
  Identifying Users

In this media activity, you are logged in as user2 and your current working directory is: /home/user2. Refer to the Class File Tree Structure by clicking the 'tree' button located on the Menu Bar and type the commands that would accomplish the requested objectives. 
Note: Be sure to press enter after each one. Click on step 1 to begin.

Lab Activity (Adobe Acrobat Reader, 40 kB)
  User Identification Commands

In this lab, you will use advanced UNIX commands to determine your identity and the identity of other users logged on to a system.