OT yum rollback (was When will Fedora work again?)

[Seth Vidal]

On Thu, 12 Mar 2009, David L wrote:

> On Tue, Mar 10, 2009 at 8:38 AM, Patrick O'Callaghan wrote:
>> On Tue, 2009-03-10 at 11:01 +0000, Frank Murphy (Frankly3D) wrote:
> <snip>
>>>
>>> Then would it be time for some sort of "rollback" utility,
>>> so if "yum update something" breaks, maybe  : yum --rollback something
>>
>> That's been discussed before. It's fantastically hard to do, short of
>> snapshotting the whole system.
>>
>>
>
> I saw this article that seems relevant to this discussion
> a few months back:
>
> http://www.linux.com/feature/155922
>
> It talks about a "next generation" package manager called
> Nix that claims to solve this kind of problem I think:
>
> http://nixos.org/
>
> Whether nix is for real or not, from a naive user's
> perspective it sure seems like it should be possible
> to solve this problem.  It basically seems like what svn
> or other version control systems already do.  They
> remember changes (and for the case of text files,
> they store only differences.  For binaries it should
> also be possible to efficiently store changes... in
> fact I seem to remember a new update feature that
> will do something like that).

binaries are only half of the problem.

You also have to worry about rolling back the users data.

if I upgrade from mysql4 to mysql5, for example and get mysql5 running 
then my databases have been converted. Now, if I rollback the binaries, 
how do I go back?

Mysql is obviously a big item and maybe not that common so let's look at a 
more common one:
firefox
evolution

these two seem to routinely change their config formats in incompatible 
ways.

How does a rollback solve that problem?

-sv