User Management Made Easy

who command displays the current active users on the server 'w' will still show the result in more compact method
Use who -uH for idle time and terminal info.

users Used to list the currently logged in users.

w Displays currently logged in users and processes they are running.

whoami To display the current username

groups Shows us the list of groups that the current user is in.
Use groups user-id to display groups for a given user.

set Used to define the environment variables normally during installation of softwares we will need to make these custom
settings

id Used to display the user id and the group id's for the user
Use id user-id to display info for another user id.

last Listing of most recent logins by users. Show where from, date and time of login (ftp, ssh, ...) Also see lastlog command.
Show last 100 logins: last -100

history Shell command to display previously entered commands.

If you wish to set a welcome message or warning messages for all SSH connections then it will be advised to add the same to /etc/issue for example and have the /etc/ssh/sshd_config
Specify text file: Banner /etc/issue

Again you can use the /etc/motd to modify the next welcome message which gets displayed on the login prompt. The file /etc/issue is used for welcome message on telnet login screen.