[Fedora-packaging] The role of %{_libexecdir} for using environment-modules

Ed Hill ed at eh3.com
Wed Oct 8 01:15:34 UTC 2008

On Tue, 7 Oct 2008 20:07:39 -0400 (EDT) Jens Petersen wrote:
> > I'm working on a couple of packages (gromacs and gromacs3) that are
> > going to use environment-modules since they have a lot of binaries
> > that
> > otherwise would go to /usr/bin and some of them have very generic
> > names
> > (e.g. wheel, luck and highway). This way a user can have both the
> > new release series and the old stable series installed and decide
> > which version to use.
> It would be better to use alternatives for this.
> Look at MTA packages or other packages that do this kind of thing
> already.
> I am not familiar with gromacs: is it really necessary to include
> both in Fedora?: normally we just tend to ship the latest major
> release. Jens

Hi folks,

*Please* stop suggesting alternatives.

Alternatives is a total failure for user-space applications that are
not *completely* generic and 100% interchangeable.  Lets illustrate
this point with three use cases:

  Use case 1 : Two users (Alice and Bob) are using the same system
    (machine) at the same time.  Alice must use MPI implementation
    "A" since it is the only one that works properly with her 
    application.  And Bob wants to use the "B" implementation since 
    it is the one that works best for his application.  Since
    alternatives is a *system-wide* setting, it can only satisfy one
    user a time -- never both.  Thus, it is a total failure for this
    use case.

  Use case 2 : A single user (Carl), wants to run two programs 
    (Foo and Bar) simultaneously.  The Foo program feeds its results
    to the Bar program.  And the Foo program requires the "A" MPI 
    implementation while Bar requires the "B" implementation.  Since 
    alternatives is a system-wide configuration setting, Carl cannot
    run the two programs at the same time.  Again, alternatives is
    not up to the task.

  Use case 3 : Dan and Evan both want to use the Baz program but Dan
    requires certain features only available with Baz v1.0 while 
    Evan must have features only present in Baz v2.0.  As in use case
    #1, both Dan abd Evan are trying to use the same machine.

Please notice that modules (aka "environment modules") is a perfectly
workable solution for all the above scenarios and it does not require
any help from an admin (or root/sudo perms).


Edward H. Hill III, PhD  |  ed at eh3.com  |  http://eh3.com/
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