Thread: Why df -h needs root for particular devices?

This command:

$ df
Filesystem 1K-blocks Used accessible Use% Mounted on
/dev/sda2 14610964 6682044 7186720 49% /
(...)

Works very well, shows space usage for all devices. But this one doesn't work:
$ df /dev/sda2
df: `/dev/sda2': Permission denied
df: no file systems processed
But, it works when implemented by root:
$ sudo df /dev/sda2

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda2 14610964 6682044 7186720 49% /

Why is it so? If I can make out space left on ALL devices, why cannot I make out it on a particular one? It's not logical, df -h without added parameters gives me additional information after all.

Look like no logic in it +1.

From "man df":

If an case is the complete file given name of a disk device node with a build up file system, df illustrates the space open on that file system rather than on the file system with the device node (which is always the root file system).

And to acquire information on the device node it wants at least read access to it.