Users

    useradd <username>

    # With no login
    useradd -r <username>
    # -r, --system
    # create a system account
    # The -r flag will create a system user - one which does not have a password, a home dir and is unable to login.

    # add user to sudo group
    # as root
    usermod -aG sudo <username>
    # -a helps to append the user to a specific group
    # -G indicates the group name to which the new user will be added

su - <username>
# You need to enter the password

userdel <username> -r
# -r (--remove) 
# force userdel to remove the user’s home directory and mail spool

# info about all the users in the system
getent passwd | sort

# check if user exists
getent passwd <username>

# list all the users from a particular user group
getent group <group_name>