Re: epoch

["Mike A. Harris" <mharris opensourceadvocate org>]

On Mon, 9 Jul 2001, Alan Eldridge wrote:

>Date: Mon, 9 Jul 2001 12:38:21 -0400
>From: Alan Eldridge <alane@geeksrus.net>
>To: RPM List <rpm-list@redhat.com>
>Reply-To: rpm-list@redhat.com
>Content-Type: text/plain; charset=us-ascii
>Subject: epoch
>
>Jeff, can you give a quick, Reader's Digest summary of epoch, and when you
>should or shouldn't use it?

"Epoch:" should be avoided as much as possible.  It creates user
confusion, and can cause many hassles.

Its usage is intended to get over the problem where a newer
version of something may have a lower sort order for example.
Some version numbering schemes of software are oddball, and when
sorted numerically, a beta might actually seem like a larger
number than the final release.  Epoch can hack around that, but
if you can do it some other way, it is best to do so.

Another thing epoch is useful for is if you have a package that
once built is dependant on a specific version of another package,
but at the source level it can be built against multiple releases
of the package it is dependant on.  ie:

foo-1.2 can be built against bar-4.5 and against bar-4.6.  You
may have shipped bar-4.5 before and now ship bar-4.6.  If foo-1.2
is built against bar-4.5 it only works with bar-4.5, and if built
against 4.6 it only works with bar-4.6.  This leaves you with a
foo package called:

foo-1.2-1 for example, but which bar package should you use it
with?  You can specify the dependancies on a specific bar version
as a build dependancy, but that isn't really correct because it
isn't really dependant on a specific version of bar at build
time.

You can instead use epoch's to solve this.  epoch 1 would be say
for the version built against bar 4.5 and epoch 2 against the
other bar.  When upgrading, a package with a higher epoch will
upgrade a package of a lower epoch regardless of version-release.

You're guaranteed to have a version of foo that matches the
version of bar.



----------------------------------------------------------------------
    Mike A. Harris  -  Linux advocate  -  Open Source advocate
       Opinions and viewpoints expressed are solely my own.
----------------------------------------------------------------------
Windows; (n):  Will Install Needless Data On Whole System