Free Trial

Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.


  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL
Help

8. Users and Groups > The Group File: /etc/group

The Group File: /etc/group

For various administrative purposes, in particular, controlling access to files and other system resources, it is useful to organize users into groups.

The set of groups to which a user belongs is defined by the combination of the group ID field in the user’s password entry and the groups under which the user is listed in the group file. This strange split of information across two files is historical in origin. In early UNIX implementations, a user could be a member of only one group at a time. A user’s initial group membership at login was determined by the group ID field of the password file and could be changed thereafter using the newgrp(1) command, which required the user to supply the group password (if the group was password protected). 4.2BSD introduced the concept of multiple simultaneous group memberships, which was later standardized in POSIX.1-1990. Under this scheme, the group file listed the extra group memberships of each user. (The groups(1) command displays the groups of which the shell process is a member, or, if one or more usernames are supplied as command-line arguments, then the group memberships of those users.)


  

You are currently reading a PREVIEW of this book.

                                                                                                                    

Get instant access to over $1 million worth of books and videos.

  

Start a Free Trial


  
  • Safari Books Online
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint