As the system is set up to handle multiple users concurrently, it needs to have in place mechanisms with which it can control the security and privacy of the file system. It needs to be able to control access to the file system resources for each individual user. In addition it also has to be able to control access at a group level i.e. users who belong to the same group can be given certain privileges with respect to the file system operations.
To be able to perform these features, associated with each file or folder are the categories (owner, group, others), and the file permissions (read (r), write (w), execute (x)), and the directory permissions (read (r), write (w), access (x)).
Associated with a file are the categories owner, group and others and the permissions which these have on the file. The userid of the user who creates a file by default becomes the owner of the file. Userids on the system are assigned to one or more groups. When a userid is created on the system, a group which has the same name as the userid is also created and the new userid belongs to this group. By default this group (which has the same name as the file owner) is associated with the file. All of the other userids on the system which are not the owner of the file or belong to the group associated with the file, are placed in the category others.
By default the owner has read and write permission for a non-executable file and read, write and execute permission for an executable file. The group associated with the file has read permission for a non-executable file and read, execute rights for an executable file. The others group has read only permission for non-executable file and read, execute rights for an executable file.
The rights and ownership concepts described above apply to directories too. However since a directory cannot be executed, access rights is substituted for execution rights. Access to a directory means that the userid with the appropriate permission can descend into the directory (i.e. change directory to it).
The File Manager application described below may be used to view and modify the ownership and permissions of a file or folder. Only the owner of a file/folder can change its permissions and only the superuser or root can change the ownership of a file/folder.
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Tutorial: Files and Folders On Your Linux Desktop
1. The File System
2. Ownerships and Permissions
3. Using the File Manager
4. Accessing Files and Programs
5. The Trash Can
6. Using A Text Editor
