When I try to edit my /etc/hostname file, using sudo nano /etc/hostname (or any other editor) I get the following:

Error writing /etc/hostname: Permission denied

I then tried:

sudo chmod u+w ./hostname

And got the error:

chmod: changing permissions of `./hostname': Operation not permitted

I get the same error trying to add write permissions to any use or group.

This is what ls shows:

-rw-r--r-- 1 root root 22 2012-06-18 12:25 /etc/hostname

Any idea why and what can I do about it?

I'm running Ubuntu 11.10.