Linux - Add User Account

To add user to Linux from command line (shell) type command adduser followed with options and username. Example to add user linips (type sudo if you are not root):

$ sudo adduser linips
Adding user `linips' ...
Adding new group `linips' (1001) ...
Adding new user `linips' (1001) with group `linips' ...
Creating home directory `/home/linips' ...
Copying files from `/etc/skel' ...
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for linips
Enter the new value, or press ENTER for the default
        Full Name []: Linips Blog
        Room Number []:
        Work Phone []:
        Home Phone []:
        Other []:
Is the information correct? [Y/n]

Defaults are in file /etc/adduser.conf

What if we are want to add user with username format as firstname.secondname?

$ sudo adduser linips.blog

adduser: Please enter a username matching the regular expression configured
via the NAME_REGEX[_SYSTEM] configuration variable.  Use the `--force-badname'
option to relax this check or reconfigure NAME_REGEX.

Then we must add --force-badname switch to command

$ sudo adduser --force-badname linips.blog

and continue with entering data for new user.