There is no command in Linux to list all the users in the system, however, using the command "$cat/etc/passwd" opens an internal data file that shows all the information regarding the users in the system. Opening the etc/passwd file lists all pertinent local user information, including password and ID.
Other information contained in etc/passwd includes login status, home directory and primary group. However, this file also lists pseudo users stored in the system, such as mail, apache or adm. These are user names that the Linux system uses to process applications and services and do not belong to a real world users.