Linux create/delete user, group, and acl

 1.  Add special user and group

group ref useradd_ref  acl_birds

#groupadd -g 4200 sysadmin2

#useradd appadmin1 -u 4100 -g 4100  -s /bin/bash 

#deluser ...

2. 　useradd command and compare adduser ref

useradd is law level
The command useradd is also used to add users. It comes with some flags.  Some of them are as follows.
-D        Defaults
-m        Creates a home directory
-s         Defines the shell for the user
-e         Date on which the user account will be disabled
-b         Base directory for the home directory of the user
-u         UID
-g         Initial group number
-G        Additional groups by name
-c         Comment