[gentoo-amd64] Re: system broken?

[Duncan]

Ben de Groot <yngwin@g.o> posted 493FB175.3050204@g.o,
excerpted below, on  Wed, 10 Dec 2008 13:09:25 +0100:

> Martin Herrman wrote:
>> thanks a lot for this link! This seems to be exactly the issue I have
>> (and also caused by the wish to have GCC 4.3). I will downgrade glibc
>> (and gcc) to have a stable system again.
>
> Except you can't downgrade glibc. It won't work. So your best bet is to
> get a tarball of portage-2.1.6 (or 2.2_rc17) from someone with a
> functioning ~amd64 system. (I myself am stuck on ~x86 for the moment.)

Well, you can, but not directly.

Surely you have an emergency boot method, either (like me) a backup root 
partition that you snapshot from your working one periodically when you 
know the system's working pretty smoothly (which means you've rebooted 
since your last merges so you know you can), or a LiveCD of some sort, 
maybe a Gentoo LiveCD, maybe something else, that you can boot to and 
mount your broken system partitions from?  That's the basis from which to 
start.  If you don't have such an emergency boot solution, how do you 
expect to recover in the event you have a broken boot?

When I had a problem with glibc and needed to downgrade, I simply stuck 
the appropriate root=/dev/whatever on the kernel command line from grub, 
and booted to my backup root partition.  The way I'm setup, that gives me 
the exact working system I had at that point, and can mount either my 
normal or backup /home and other data partitions, so I'm still fully 
operational.  I was able to mount my my normal root from the backup, 
along with my packages partition, then set ROOT= to point to the normal 
working partition, and emerge -K an appropriate binpkged glibc over top 
of the broken one.  I must admit I was a bit apprehensive about it as I'd 
never used portage's ROOT= setting before, and after all this is glibc 
we're talking about, but it worked fine, and I was then able to reboot 
back into my normal root again.

Another alternative as long as glibc isn't so broken you can't run 
anything, is to hand-edit the ebuild to kill the downgrade blocker bit of 
the script.

Finally, as posted elsewhere, it's also possible to start with a stage 
tarball once again as a known good starting point, then emerge --
emptytree @system to get back to a current system.  This is sort of the 
equivalent of an OS reinstall on other OSs/distributions and it works 
quite well.  Of course, it helps if you make a backup of your /etc before 
you do it, so you can quickly recover overwritten config files.

So there's ways to downgrade glibc.  You just have to be smarter than the 
child-safety-locks portage has in place to prevent you from doing it 
inadvertently and breaking a system further, as doing so after remerging 
a bunch of packages thus linking them to the new glibc might do.  But if 
you have a backup to operate from if necessary, you don't have to worry 
so much about breaking a system which is probably already partially 
broken or you'd not be having to worry about downgrading glibc.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman