Re: [gentoo-user] Re: Heads Up - glibc-2.27 breaks my system

[Dale]

Nikos Chantziaras wrote:
> On 03/02/18 07:54, Dale wrote:
>> While on this topic, I have a question about glibc.  I have it set in
>> make.conf to save the binary packages.  Generally I use it when I need
>> to go back shortly after a upgrade, usually Firefox or something.
>> However, this package is different since going back a version isn't a
>> good idea.  My question tho, what if one does go back a version using
>> those saved binary packages?  Has anyone ever did it and it work or did
>> it and it fail miserably?
>
> It is perfectly fine to downgrade glibc if you didn't emerge anything
> that compiled binaries.
>
> If you did, you can still downgrade, but then you need to rebuild the
> packages that you emerged since the glibc upgrade. qlop is your friend
> here; it lets you find out the dates on which you emerged packages.
>
> This whole thing is not actually special to glibc. Other libraries
> work in a similar manner. You can't just link other software against a
> new version of the library, then remove the library and replace it
> with an older one. It might result in breakage. But glibc is used by
> almost everything, it's not "just a library", it is *the* library, and
> so it has a special protection to prevent a downgrade. You can bypass
> that protection and downgrade anyway, but then you need to know what
> you're doing and how to restore your system correctly. If any
> sys-devel packages are affected, you might not be able to do it. If
> only end-user packages are affected which are not used during an
> emerge, then it's quite safe to downgrade.
>
>
>

That makes sense.  So, if worse comes to worse, downgrade, then emerge
-e world if unsure what all has been updated since.  If, using qlop or
friends, you can figure what was done since the upgrade, emerge those to
make sure the linking is correct.  At least that is a option that should
be doable.  That's better than thinking you can't downgrade for any
reason, period. 

I wonder, is this sort of info on Gentoo's wiki?  If not, shouldn't it
be?  I've always read that downgrading is a bad idea and strongly
discouraged but if one runs unstable on a regular basis or just hits
that random corner case bug, one may run into this even if one doesn't
have the experience to know how to put the broken pieces back together
again. 

Thanks for the info.  At least there is a option, even if it might get
interesting.  ;-)

Dale

:-)  :-)