linux file system permission issue

Question

I'm deploying nutch. At first I just left the index file under /root/nutch1.0. This works fine when run from command line. However, when I search from web, it always returns 0 hit.

I finally found the reason: It's because the index file is located under /root that causes the failure to open the file. Things returned to normal when I move the index file to another directory.

But my question is:

I didn't change the permissions of the index file (just cp xxx another-directory). Why did the access rights change?

drwxr-x--- 12 root root    4096 Jun  1 14:49 root
drwxr-xr-x 14 root root    4096 Nov 16  2007 usr

I put files under /usr and it worked.

Answer 1

Because you can't access anything in the root directory unless you're root.

Look at the permissions on /root, it should be something like 700... the execute bit is set so than only root can "execute" the directory. Execution permissions on a directory are what allow you to look at files inside the directory.

It's the same reason you can't "ls /root" while you're logged in as someone else.

Answer 2

To read a file, you need search ('x') permission on the directory the file is in, as well as read permission on the file itself. Moving the file from a directory where the web server does not have search permissions to one where it does will cause the effect you see.

Answer 3

Presumably you're in group "root", and therefore can use the directory. When using a web interface, you're likely in a program with its own user (in the Unix/Linux sense), which is probably not in group "root". From the permissions you've listed, anybody can use the "/usr" directory.