создать нового пользователя или обновить информацию о новом пользователе по умолчанию (create a new user or update default new user information)
Предостережение (Caveat)
You may not add a user to a NIS or LDAP group. This must be
performed on the corresponding server.
Similarly, if the username already exists in an external user
database such as NIS or LDAP, useradd will deny the user account
creation request.
Usernames must start with a lower case letter or an underscore,
followed by lower case letters, digits, underscores, or dashes.
They can end with a dollar sign. In regular expression terms:
[a-z_][a-z0-9_-]*[$]?
Usernames may only be up to 32 characters long.
