GROUP(5,F)                  AIX Technical Reference                  GROUP(5,F)



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group



PURPOSE

Identifies a group.

DESCRIPTION

Users can be assigned to one or more groups, each of which share certain
protection privileges.  The person who sets up the system may want to place
users in the same group because they need access to a common set of files.
Similarly, a certain group of users can have access restricted to certain
files.

When users log in, they are assigned to the group specified in the
/etc/password file.  In addition, they are assigned as a member of all groups
specified in this file.  Users are allowed to access any files that the group
to which they are assigned has access.  However, any files created by the user
can be accessed only by the members of the primary group of which that user is
a member.  A user is allowed to change his primary group for the duration of
the terminal session using the newgrp command.

The /etc/group file defines to which groups a user has membership.  Each line
in this file defines a group and consists of four fields separated by colons.
It contains the following information for each group:

Note:  In the multibyte environment, the group file may contain only ASCII
       characters.

Group            Description

group name       A character string of up to eight characters that references
                 the group.

password         This field is optional.  If specified, anyone attempting to
                 enter the group must correctly supply the password to the
                 system.

group ID         A number assigned to the group and used in access decisions.

user group list  A list that specifies the login names of all users allowed in
                 the group.  User IDs in the list are separated by commas.  The
                 user group list may contain up to 500 eight-character login
                 names.

In newly distributed systems, there are typically only two groups:  the staff
group and the system group.  New users can be added to groups and new groups
can be added as necessary.




Processed November 7, 1990        GROUP(5,F)                                  1

GROUP(5,F)                  AIX Technical Reference                  GROUP(5,F)



If several users wish to share the same privileges, including the ability to
terminate each other's processes as well as to access the files of others, the
same numerical user ID can be assigned to each.  This mechanism is sometimes
used to give the same person several accounts on the system, each with
potentially different login directories and other characteristics, such as
electronic mailboxes or login programs.  For example, the operator has the same
user ID, and therefore superuser authority.  However, this operator typically
uses a restricted version of the shell that does not give access to commands
that allow reading the files of others.

EXAMPLE

The following is an example of the /etc/group file.  This is an ASCII file.
Each group is separated from the next by a new-line character.  The fields are
separated by colons.  Because the password is encrypted, it can be used to map
numerical group IDs to names without concern of compromise to user security.

     system::0:su,bill,jack,gary
     staff::1:
     bin::2:su,bin
     sys::3:su,bin.sys
     adm::4:su,bin,adm
     mail::6:su
     usr::100:guest

FILE

/etc/group

RELATED INFORMATION

In this book:  "passwd."

The newgrp, passwd, and users commands in AIX Operating System Commands
Reference.




















Processed November 7, 1990        GROUP(5,F)                                  2