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

15. File Attributes > File Permissions

File Permissions

In this section, we describe the permission scheme applied to files and directories. Although we talk about permissions here mainly as they apply to regular files and directories, the rules that we describe apply to all types of files, including devices, FIFOs, and UNIX domain sockets. Furthermore, the System V and POSIX interprocess communication objects (shared memory, semaphores, and message queues) also have permission masks, and the rules that apply for these objects are similar to those for files.

Permissions on Regular Files

As noted in Retrieving File Information: stat() , the bottom 12 bits of the st_mode field of the stat structure define the permissions for a file. The first 3 of these bits are special bits known as the set-user-ID, set-group-ID, and sticky bits (labeled U, G, and T, respectively, in Figure 15-1). We say more about these bits in Set-User-ID, Set-Group-ID, and Sticky Bits. The remaining 9 bits form the mask defining the permissions that are granted to various categories of users accessing the file. The file permissions mask divides the world into three categories:


  

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