Re: Dependency problem when "post" runs command from the rpm

[Toralf Lund <toralf@xxxxxxxxxxxxxx>]

Jeff Johnson wrote:
> 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 [ ... ]
> >
> > Perhaps my understanding is wrong - but I believe:
>
>
> Um, yes, wrong.
>
> > [ .. ]
>
> The %pre and %post scripts are run immediately before/after a package 
> is installed,
> not after all the packages are installed.
Exactly. This is what's causing me trouble; essentially, I have a 
command that would be better to run at the end of the entire 
transaction. But I think I understand why rpm doesn't work that way...
> 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.
Quite.
> [ ... ]
>
> 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.
In my case the script and the package itself both need (more or less) 
the same libs. Logically, they may be seen as independent sets of 
dependencies, though, I think...
> 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
Well. It doesn't help me too much with my original issue. But, like I 
said elsewhere, I can't seem to reproduce the problem I thought I had, 
so maybe it doesn't matter. I'm still confused, though.

Question: Can I generally assume the packages are ordered according to 
"Requires" these days, i.e. that if package A requires something 
provided by package B, then B is installed before A (when A and B are 
both part of the same transaction)? I'm fairly sure I couldn't when I 
started using rpm, so I had to mess about with ""PreReq" instead...
> 73 de jeff
>
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