File Protection and Permissions

UNIX/Linux/Mac uses a set of 9 access control bits, in three groups of three. These correspond to R (read), W (write), and X (execute) permissions for each of the Owner of the file, the users in the Owner's Group, and all Other users of the device (that aren't the owner or in the owner's group.)

A string that allows all of the permissions to all three user categories looks like: rwxrwxrwx. The leftmost triple, rwx, is for the Owner, and tells that the owner can read from, write to, and execute the file. The middle triple, rwx, is for the users in the Owner's Group, and the rightmost triple, rwx, is for any Other user of the device.

When a permission is NOT granted, a dash - appears instead of the corresponding letter. For example, rwxr--r-- means that the the owner can read from, write to, and execute the file, but the users in the Owner's Group and any Other user can only read the file's content, without being allowed to change the file or execute it.