Hi,
I have noticed that on my Linux box there is a nice feature which make it impossible for specified member (owner, group or other) to have an given access if a member from which we would expect it more don't have that access.

So it is impossible to read file by all if others have set read bit but owner or group doesn't have.

But I haven't found that the above feature is guaranteed by any standard. So is it on which really I can rely on?

By the way: I have observed that even experienced users has sometimes problems when asked if a given structure of permissions will give a specified member access to such-and-such operations on the file and on the contents of the file. In the fact that subject isn't really clearly explained even in the books in which I was looked for it.

So to systematize it, what I have found/observed:
- if you want to run native Linux application then x permission is enough to execute it. But it is not the case if you want to run shell (sh, bash, ...) script - then you need to add r permission. As far as I know that it is caused by the fact that shell uses system call read() to read from file,

- if you haven't permission to read directory then it is impossible for you to list a contents of that directory. But still it is possible to read, write and execute files (if they have neccessary permissions); otherwise Linux permissions are not inherited, so if subdirectory has a read permission then it is possible to list files which are in it.

- if you haven't permission to execute directory then it is impossible to read inode of that directory (it is arbitrary arranged that it has completely different meaning from x permission for usual files - it has nothing in common with real executing). Basically it means that you can't cd to it. If a directory "dir" hasn't x permission and there is a file "textfile" in that directory you will not have access to that file. But if you have a subdirectory "subdir" in "dir" then permissions of "subdir" are on his own. For example if it has rwx permissions it is possible to cd to that directory and then successfully edit and write to file.

- if you haven't w permission to a directory then it is possible for you to write to it. But it is possible for you to write to files in that directory.

Please inform me if something from which I have written above is not true - part of that is from my observation. I would be grateful for other examples where one could be confused about permissions and how it affect system file.

Thanks in advance for responses.