On Sep 15, 2008, at 11:24 PM, Michael A. Peters wrote:
Toralf Lund wrote:
I've run into an installation order issue related to the "post"
scriptlet in one of my packages. Basically, this scripts executes a
(command-line only) program installed by the package, and this
program pretty much needs everything required by the package. The
problem is, if I install my package along with some of the required
software, the requirements are often installed *after* the "main"
package - which means the "post" script won't work because some of
what the program needs isn't installed yet.
So, this is when I use "Requires(post)", isn't it? But how do I set
it up? The Requires of the package is a very long list, and most of
the entries are added via the "AutoReqProv" mechanism, so
duplicating the info by hand for "Requires(post)" is rather hard.
Is there an alternative? Can I somehow say that everything in the
main Requires list is also required by "post"? Or alternatively,
can I enable automatic search for shared objects etc. for
Requires(post) just like for Requires?
Perhaps my understanding is wrong - but I believe:
Um, yes, wrong.
Requires(pre) is when something is required for a pre-install script.
Requires(post) is when something is required for a post-install
script but not necessarily for the package itself - IE you could
remove the dependency after the post script has run.
When installing a group of RPMs together, the post scripts are not
run until after all the packages are installed - so if foo requires
bar and the foo post script needs bar installed - just Requires: bar
should ensure that bar is actually installed before the foo post
scriptlet runs.
The %pre and %post scripts are run immediately before/after a package
is installed,
not after all the packages are installed.
This is also true for %preun/%postun when a package is erased, the
scripts are run
immediately before/after the erasure.
My understanding of this may not be 100%
What is most confusing is that rpm does install before erase. Which
means that %post
scriptlet is run before %preun is run, which is perhaps counter-
intuitive, but is exactly
what is needed if shared libraries are being upgraded on live systems.
The new librrary
must be installed before the old library is removed in ordeer to
minimize the window
where the library is not available.
Another confusion is the relationship on upgrade between the new
installed package and
the older erased package(s) (note that Obsoletes: can/will lead to
multiple packages to be
erased). rpm has never guaranteed any relation between installed <->
erased package
ordering other than "Erasing is after install." As originally
implemented, erasing was immediately
after install. Nothing wrong with that except that forces the erasure
to happen before
the next install is attempted, whgich is slower than delaying all
erasures until later,
as erasures can always be run in parallel (assuming that erasure
dependencies
are accurate and that erasures are well ordered, but even those
details usually
don't matter on upgrade).
And finally that brings the topic to context markers like
Requires(post) etc.
Context markers like Requires(post) are intended to break dependency
loops while
ordering.
A package that "needs" some other package solely while running a %post
scriptlet,
not after being installed, can carry a Requires(post) hint to the
ordering within rpm.
The hint excludes dependency loops between install <=> erase packages.
The other major affect of adding an explicit Requires(post) hint is
that those
dependencies are not registered in an rpmdb because they were needed
solely
for installing, not for using or erasing, a package. There's no need
to keep track
of the install context dependencies after the install has been done
because
the %post scriptlet is run only during install, never run after install.
hth
73 de jeff
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