Thinking in a Simple Way


What do r w and x really mean for a directory in Unix Shell environment?

A directory is a file too, and “read” permission means you can read it. But you really cannot do very much without x permission as well. With directories, you usually have both read and execute permission or neither. On a directory, that x is officially called “search permission”. You need x to use a directory in a pathname. So if you try “cat /etc/passwd”, you will need x on / and /etc. You also need x to cd into a directory. Suppose you have read but not search (x) permission on a directory. What can you do? Not much. You can use “ls” to view the file names. Even “ls -l” will not work. Read access without search permission is not very useful. Still that is better than having only write permission on a directory…that is completely useless. I have not seen any other documentation that states this explicitly, so let me repeat it: write but no execute permission on a directory grants nothing at all.Suppose you have search (x) permission but no read permission on a directory. Now you can open files in the directory if you happen to know the file’s name. You can cd into the directory. And that is it. You cannot even create a new file. Adding write permission will allow you to create files. And you can then delete files if you happen to know their name.

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