7:45 a.m.
Fedora has shipped "alternatives" for a while now, but I still don't get
it.
Why is "alternatives" better than setting your PATH appropriately? Why
should "alternatives" override your path?
The notion of having an "editor" symlink which points to vim/emacs seems
okay at first, but in practice, who's not going to just type 'emacs'?
If "alternatives" exists for the convenient use of users, I think that
the UI needs work. Every time I need to configure a new alternative, it
takes me quite a while to figure out what all the appropriate flags are
(in particular, the "link" field seems to require knowledge of where
"alternatives" is storing its directory of symlinks-- shouldn't this be
automagic via a alternatives configuration file? The result should be
that you would only need to provide name and path.)
I ask these questions sincerely hoping for answers-- I'm not trying to
be difficult. At the moment, it seems like it'd be saner to NOT have
alternatives, since I don't see what advantages the extra hoop-jumping
yields.
-Ed
PS: My latest experience went like this:
1. installed sun jdk to /opt/jdk
2. export PATH=/opt/jdk/bin:$PATH
3. cd into one of my java code bases
4. ant
5. gcj is invoked by ant, apparently due to alternatives.
6. gcj can't compile my code and I'm sad.
8:12 a.m.
Edwin Olson wrote:
Fedora has shipped "alternatives" for a while now, but I
still don't get
it.
Why is "alternatives" better than setting your PATH appropriately?
There are cases where "alternatives" are appropriate (with no better
implementation alternative), and there are cases were alternatives is not
appropriate.
Using alternatives soley to avoid augmenting $PATH is not. jpackage's use
of alternatives is imo appropriate, since it does a lot more than what can
be accomplished via setting PATH.
-- Rex
8:17 a.m.
On Fri, 2006-10-06 at 08:45 -0400, Edwin Olson wrote:
Fedora has shipped "alternatives" for a while now, but I
still don't get it.
Why is "alternatives" better than setting your PATH appropriately? Why
should "alternatives" override your path?
The two big reasons I'm familiar with are:
1) not everything respects your path (e.g. may be executed outside the
context of your login).
2) it's a convenient way to manage a group of "pointers" which all must
be updated in lock-step (e.g. getting any one of many links wrong can be
disastrous).
The context I'm most familiar with is the use of alternatives for
modifying your MTA (e.g. postfix vs. sendmail) for which both above
points are critical. Whether alternatives is appropriate for some other
scenario/context could be debated but alternatives does serve a useful
purpose.
--
John Dennis <jdennis(a)redhat.com>
8:57 a.m.
Once upon a time, Edwin Olson <eolson(a)mit.edu> said:
Fedora has shipped "alternatives" for a while now, but I
still don't get it.
Why is "alternatives" better than setting your PATH appropriately? Why
should "alternatives" override your path?
Many many many shell/perl/etc. scripts and mail clients call
"/usr/sbin/sendmail" (or even still "/usr/lib/sendmail") to submit an
email message. Any local MTA needs to provide that program, but with
RPM, you can only install one program that provides it.
With alternatives, you can (for example) install both sendmail and
postfix, and use the alternatives system to select which one is called
when "/usr/sbin/sendmail" is run.
You may want to have both installed while converting a system (so you
can be preparing and testing one as a replacement for the other). Also,
if both included their own "/usr/sbin/sendmail", the RPMs would
conflict, making it difficult for the average user to convert from one
to the other (since both provide "smtpdaemon" which is required by a
number of other packages). You can't "rpm -e sendmail; rpm -i
postfix*rpm" due to dependencies. You can use the yum shell to do
things like this now, but there is no nice GUI way to do it.
PS: My latest experience went like this:
1. installed sun jdk to /opt/jdk
2. export PATH=/opt/jdk/bin:$PATH
3. cd into one of my java code bases
4. ant
5. gcj is invoked by ant, apparently due to alternatives.
6. gcj can't compile my code and I'm sad.
If you used the jpackage nosrc SRPM to install the Sun JDK, it would
have been much easier, as it properly uses alternatives to select a JDK.
--
Chris Adams <cmadams(a)hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.
10:12 p.m.
Edwin Olson <eolson(a)mit.edu> wrote:
Fedora has shipped "alternatives" for a while now, but I
still don't get it.
Why is "alternatives" better than setting your PATH appropriately? Why
should "alternatives" override your path?
The notion of having an "editor" symlink which points to vim/emacs
seems okay at first, but in practice, who's not going to just type
'emacs'?
Or get terminally confused when <TypeSomeFunkyCommandHere> does something
completely unexpected... this really makes very little sense.
But for selecting the right lpr, or sendmail, or... from a collection of
alternatives that might be installed side by side it does make sense. Sure,
for just one it would be OK to tweak the PATH, but for a half dozen
alternates it gets very messy.
--
Dr. Horst H. von Brand User #22616 counter.li.org
Departamento de Informatica Fono: +56 32 2654431
Universidad Tecnica Federico Santa Maria +56 32 2654239
Casilla 110-V, Valparaiso, Chile Fax: +56 32 2797513
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participants (5)
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Rex Dieter