osx man page for group

GROUP(5)						      BSD File Formats Manual							  GROUP(5)

NAME
     group -- format of the group permissions file

DESCRIPTION
     The file </etc/group> consists of newline separated ASCII records, one per group, containing four colon ':' separated fields. These fields
     are as follows:
	   group     Name of the group.
	   passwd    Group's encrypted password.
	   gid	     The group's decimal ID.
	   member    Group members.

     The group field is the group name used for granting file access to users who are members of the group.  The gid field is the number associ-
     ated with the group name.	They should both be unique across the system (and often across a group of systems) since they control file access.
     The passwd field is an optional encrypted password.  This field is rarely used and an asterisk is normally placed in it rather than leaving
     it blank.	The member field contains the names of users granted the privileges of group.  The member names are separated by commas without
     spaces or newlines.  A user is automatically in a group if that group was specified in their /etc/passwd entry and does not need to be added
     to that group in the /etc/group file.

INTERACTION WITH DIRECTORY SERVICES
     Processes generally find group records using one of the getgrent(3) family of functions.  On Mac OS X, these functions interact with the
     DirectoryService(8) daemon, which reads the /etc/group file as well as searching other directory information services to determine groups and
     group membership.

FILES
     /etc/group

SEE ALSO
     passwd(1), setgroups(2), crypt(3), getgrent(3), initgroups(3), passwd(5), DirectoryService(8)

BUGS
     The passwd(1) command does not change the group passwords.

HISTORY
     A group file format appeared in Version 6 AT&T UNIX.

Mac OS X							   July 18, 1995							  Mac OS X