Directory Access Permissions/Representation

Directory is represented as a file where the data block where each files/subdirectory inside it has an entry:

• Name of file/subdirectory
• inode number

Therefore, when we list directory, we read the names from each entry. When we add/rename/remove files/subdirectories, we update the file by adding/updating/removing the entry that corresponds to the file we added.

Meaning of access permissions on a directory:

• read: List files in the directory
• write: Add/remove/rename files in the directory
• execute: Search/lookup files in the directory. It allows us to change into the directory. execute permission is needed to do anything with a directory. Even if we have read or write permissions, we can NOT do anything w/o execute permission.

touch test              // would create a directory with rwx permissions
chmod u-x test          // Remove execute permission
cd test                 // Error: permission denied
touch test/test.txt     // Error: permission denied

We as users never update directory file directory, ONLY kernel does the update and we only get to read its entries.