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3.4.5. Creating Group Directories

System administrators usually like to create a group for each major project and assign people to the group when they need to access that project's files. With this traditional scheme, file managing is difficult; when someone creates a file, it is associated with the primary group to which they belong. When a single person works on multiple projects, it becomes difficult to associate the right files with the right group. However, with the UPG scheme, groups are automatically assigned to files created within a directory with the setgid bit set. The setgid bit makes managing group projects that share a common directory very simple because any files a user creates within the directory are owned by the group which owns the directory.
For example, a group of people need to work on files in the /opt/myproject/ directory. Some people are trusted to modify the contents of this directory, but not everyone.
  1. As root, create the /opt/myproject/ directory by typing the following at a shell prompt:
    mkdir /opt/myproject
  2. Add the myproject group to the system:
    groupadd myproject
  3. Associate the contents of the /opt/myproject/ directory with the myproject group:
    chown root:myproject /opt/myproject
  4. Allow users to create files within the directory, and set the setgid bit:
    chmod 2775 /opt/myproject
At this point, all members of the myproject group can create and edit files in the /opt/myproject/ directory without the administrator having to change file permissions every time users write new files. To verify that the permissions have been set correctly, run the following command:
~]# ls -l /opt
total 4
drwxrwsr-x. 3 root myproject 4096 Mar  3 18:31 myproject