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Shared folder in linux

Suppose that we want to create a folder in which multiple users will have full access (which means that they will be able to read, write, and execute).

  1. We create the folder (under ‘/’ in this example, although it can be anywhere else):

    sudo mkdir test

    which has the following permissions:

    drwxr-xr-x 2 root root 4096 Oct 23 13:07 test

  2. We make a new group of users (“testers”):

    sudo groupadd testers

    and then we add to this group all users we want to have access:

    sudo usermod -a -G testers testuser

    (id testuser will return the groups that the testuser belongs to)

  3. We change the permissions of the shared folder (this is more useful if we have copied or moved a folder with some contents already):

    sudo chgrp -R testers /test
    sudo chmod -R g+rwx /test

    so as every user in the groups “testers” can access the folder.
    However, when a user creates a file, it is assigned with the permissions set by the user and its primary group, e.g.

    -rw-rw-r-- 1 testuser testuser 0 Oct 23 14:21 tempfile

  4. In order to automatically assign the permissions of the group when creating files and folders in the shared folder, we assign the “s” option (for setting the group id – SGID):

    chmod -R g+s test

    For example:

    drwxrwsr-x 2 testuser testers 4096 Oct 23 14:34 newdir
    -rw-rw-r-- 1 testuser testers 0 Oct 23 14:35 newfile

    Now everyone in the “testers” groups can create, edit, delete, etc. the contents of this folder.

Useful articles:
[1] “How can I give write-access of a folder to all users in linux?”, Superuser.com, retrieved on Oct 23, 2014
[2] “Using SGID to Control Group Ownership of Directories”, Yale University Library Workstation Support / Yale University Library, retrieved Oct 23, 2014
[3] “Linux chmod command sticky bit example and implementations”, ComputerNetworkingNotes.com, retrieved Oct 23, 2014