File and directory access modes

Every file has an owner. For new files, the user who creates the file is the owner of that file. The owner assigns an access mode to the file. Access modes grant other system users permission to read, modify, or execute the file. Only the file's owner or users with root authority can change the access mode of a file.

There are the three classes of users: user/owner, group, and all others. Access is granted to these user classes in some combination of three modes: read, write, or execute. When a new file is created, the default permissions are read, write, and execute permission for the user who created the file. The other two groups have read and execute permission. The following table illustrates the default file-access modes for the three classes of user groups:

The system determines who has permission and the level of permission they have for each of these activities. Access modes are represented both symbolically and numerically in the operating system.