Re: [gentoo-user] two glibcs with different version

[Alan McKinnon]

On Saturday 01 May 2010 10:57:31 Kraus Philipp wrote:
> On 01.05.2010 um 10:32 wrote Volker Armin Hemmann:
> > On Samstag 01 Mai 2010, Graham Murray wrote:
> >> Kraus Philipp <philipp.kraus@×××××××××.de> writes:
> >>> Hello,
> >>>
> >>> I must test a software with a older version of the glibc. I run the
> >>> 2.11.1 now but for one tool I need a previous version (2.6.1).
> >>> How can I compile the glibc without changing my system glibc. I
> >>> would
> >>> like to set the previous glibc with the LD_PATH.
> >>> Can I run two different versions or is a better solution to
> >>> downgrade
> >>> the system glib?
> >>
> >> I think that the only way you can do this is to create a chroot jail,
> >> in which you build everything using the old version of glibc (in a
> >> very
> >> similar way to building a new Gentoo system) and run your
> >> application in
> >> that.
> >
> > no, you can install glibc in /usr/local and then tell apps to either
> > use the
> > libs in /usr/local or /usr.
> >
> > It is just not easy because it easily breaks stuff in horrrible to
> > fix ways.
>
> Okay, can I downgrade my glibc? My Gentoo isn't a big system, it's a
> server
> installation, so I can recompile the whole system. I had forgotten to
> mask the
> glibc on the last update. I have add a line to the portage.mask but
> emerge says
> that it can't compile the older version, because will damage the system.

There is a way to downgrade, but it's far from bullet proof. You might end up 
with mutually incompatible code versions that makes the recompile world freak 
out.

First, quickpkg your existing glibc
Then read the glibc ebuild. You can bypass the version checks, IIRC its an 
envvar something like "I_AM_VERY_STUPID_OR_VERY_BRAVE". Failing that, just 
comment out the version checks, redigest the ebuild and run it.
The rebuild world

Obviously, this is not for the faint of heart.

-- 
alan dot mckinnon at gmail dot com