Try running this command to get the users in the system:
awk -F'[/:]' '{if ($3 >= 1000 && $3 != 65534) print $1}' /etc/passwd
There are more answers here: http://askubuntu.com/questions/410244/a-command-to-list-all-users-and-how-to-add-delete-modify-usershttps://askubuntu.com/questions/410244/a-command-to-list-all-users-and-how-to-add-delete-modify-users