Safest way to go from x86 to x86_64

[Matt McCutchen]

On Tue, 2010-12-14 at 14:07 +0000, Paul Johnson wrote:
> Hi,
> 
> My main box decided to snuff it last week (motherboard and processor
> decided to fry). My erstwhile friend in the computer shop I use has
> said that he has a nice 64 bit processor and motherboard going for a
> small amount of money.
> 
> The problem I have is that if I go the 64 bit route then I'll need to
> install the 64 bit OS (I can stay 32 bit, but what's the point with
> 8Gb of memory).
> 
> Is there a safe way to install the x86_64 system over the 32 bit
> version and then clean off the 32 bit stuff that is no longer needed?

I did that to my Fedora 11 system in October 2009.  It took a
significant amount of manual work and scripting and I hit a number of
minor issues.  I'm not sure I would call the procedure "safe", but it
did work.  The procedure was like this:

- Change /etc/rpm/platform to x86_64-redhat-linux and put
"%_transaction_color 3" in /etc/rpm/macros .
- Install the x86_64 kernel and boot to it.
- Install the x86_64 version of rpm.
- Construct a yum script with "install" lines for the x86_64 versions of
all installed packages.  Repeatedly try to run the script and add
"erase" lines for any i?86 packages that cause file conflicts until it
succeeds.
- Watch the output.  When scriptlets fail, fix things manually.
- Remove all unneeded i?86 packages.  I needed to keep a few proprietary
packages that are only available for i?86, so I used a script to walk
the dependencies and figure out which i?86 packages could be removed.

YMMV with rawhide.

-- 
Matt