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From: tp@ndm20
Newsgroups: net.sources.bugs
Subject: Re: What happens during an unlink(2
Message-ID: <900001@ndm20>
Date: Sat, 24-May-86 09:17:00 EDT
Article-I.D.: ndm20.900001
Posted: Sat May 24 09:17:00 1986
Date-Received: Tue, 27-May-86 07:24:49 EDT
References: <341@adiron.UUCP>
Lines: 14
Nf-ID: #R:adiron.UUCP:341:ndm20:900001:37777777600:896
Nf-From: ndm20!tp    May 24 08:17:00 1986


The problem of  zeroing a  file no  longer in  use is  tricky in unix
because the user has no way to delete a file.  rm  simply unlinks it,
i.e.  removes it from a directory.   Others have  mentioned that this
does not imply that there are no other links, and indeed  in order to
rm a file, you do not need any permission to read or  write it, since
an rm is a function applied to the  containing directory  and not the
file itself.  What is needed  is code  in the  kernel to  zero a file
after the last link is removed.  The kernel implicitly deletes a file
with no links.  This is the only time  the zeroing  could take place.
Of  course  systems  not  worried  about  security  wouldn't want the
overhead.  Maybe this should be a configuration parameter.  Of course
it would be nice if it were  filesystem dependent,  then you wouldn't
have to have the overhead on "non-secure" file systems.