By default, user and group names are checked against the configurable regular expression NAME_REGEX (or NAME_REGEX_SYSTEM if --system is specified) specified in the configu?
ration file. This option forces adduser and addgroup to apply only a weak check for validity of the name.
is the default action if the program is invoked as addgroup.
Add the new user to GROUP instead of a usergroup or the default group defined by USERS_GID in the configuration file. This affects the users primary group. To add addi?