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From: "David S. Miller" <davem@redhat.com>
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Date: Mon, 30 Apr 2001 12:07:44 -0700 (PDT)
To: root@chaos.analogic.com
Cc: Torrey Hoffman <torrey.hoffman@myrio.com>,
        "'Kenneth Johansson'" <ken@canit.se>,
        Jonathan Lundell <jlundell@pobox.com>, linux-kernel@vger.kernel.org
Subject: RE: 2.4 and 2GB swap partition limit
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Richard B. Johnson writes:
 > On Mon, 30 Apr 2001, Torrey Hoffman wrote:
 > > In general, is there a safe way to replace executable files for
 > > programs that might be running while their on-disk images are
 > > replaced?
 > 
 > Yes. Perfectly safe:
 > 
 > mv /usr/bin/exeimage /usr/bin/exeimage.sav
 > cp /wherever/exeimage /usr/bin/exeimage
 > 
 > 
 > The executing task will continue to use the old image until it exits.

Even more effective is:

mv /wherever/exeimage /usr/bin/exeimage

The kernel keeps around the contents of the old file while
the executing process still runs.

This is also basically how things like libc get installed.
A single mv is not only preserves currently referenced contents,
it is atomic.

Later,
David S. Miller
davem@redhat.com
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