HOW TO VIEW SYSTEM USERS IN LINUX
A fundamental part of system administration is configuring and managing users and groups. Part of this task involves monitoring the log in capabilities of all system entities.
In this video you will see the command to see a list of all users in the passwd file.
cat /etc/passwd
Next you will see how to shorted that and just see the users.
cut -d : -f 1 /etc/passwd
You will also see how to see all groups
cat /etc/groups
and then see how to get a list of groups only
cut -d : -f 1 /etc/group
This tutorial was filmed on Centos but it should work for all Linux versions such as Ubuntu