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From: barmar@think.com (Barry Margolin)
Subject: Re: Saving a file in emacs without the right permission bits
Message-ID: <1991Apr19.052504.2074@Think.COM>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
References: <1991Apr18.220342.25107@sj.ate.slb.com>
Distribution: usa
Date: Fri, 19 Apr 91 05:25:04 GMT

In article <1991Apr18.220342.25107@sj.ate.slb.com> konath@sj.ate.slb.com (Kannan Konath) writes:
>  I alter the file and when I try saving it, emacs responds by
>asking me whether I really want to save the file, to which I reply
>yes.  It saves the file and changes the ownership of the file to
>the new user.
>Isn't it illegal for another user to be able to overwrite a file over
>which he does not have "w" status?  

Yes -- that's why it asks permission first :-)

Actually, it's not overwriting the file, and it's not changing its
ownership.  GNU Emacs renames the old file to filename~ or
filename.~<version#>~, and then creates a *new* file with the old file's
name.  Since you created the new file, you are its owner.

The only access you need to do this is write access to the directory; the
access on the file itself doesn't matter, because you aren't actually
modifying the file, just the directory entry that refers to it.

To verify this, use "ls -i" before and after saving the file, and notice
that it has a different inode number.
 
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar