Hi,

I've got a lenny installation running a 32-bit kernel (2.6.25-2-486) on a 64-bit machine.

I want to install a 64-bit kernel; my googling hasn't turned up any useful guide.

How do I accomplish this, please?

You need to install using the "x86_64" installer rather than "i386". One thing to note with a 64-bit system:

Many proprietary closed-source programs will not run on a 64-bit system, so if you use Skype, Acrobat Reader, Flash, and any other number of such software, you will need to install and maintain some 32-bit libraries as well ("mixed" system)

I don't know of any convenient way to switch from a 32-bit system to a 64-bit system, so I would recommend a reinstall.

You must reinstall using an "amd64" installer (there is no "x86_64" installer in Debian), I recommend installing a recent testing (Lenny) version like "testing-amd64-netinst.iso" if you have internet access during the install. Some applications, like Adobe's flash plugin, are still 32-bit, but they run fine on a 64-bit system through the nspluginwrapper package. The 64-bit version of Debian has come a long way in the past few years, to the point that many 64-bit users (like myself) have now gotten rid of their 32-bit backup installation (had that around "just in case", but never used it anymore).

If you mean drop a 64-bit kernel into a 32-bit installation of Linux, that won't work.

You can drop in replace a 32-bit kernel with some very different 32-bit kernels (replace non PAE with PAE, etc.) without disturbing the rest of the installation. But you can't do that with a 64-bit kernel.

32-bit programs can run with a 64-bit kernel, so you might expect a whole Linux installation of 32-bit programs would run with a 64-bit kernel. But it doesn't. I'm not expert enough to what what extra pieces would be required.

I'm sure a real Linux guru could add/change just a few things in a 32-bit install of Linux to enable everything to run under a 64-bit kernel. But I've never heard of anyone packaging that for ordinary users. I use a Debian based distribution, in which that sort of kludge would be even harder than it would be in some other distributions, such as Red Hat based. Maybe in some distributions it isn't even hard. I haven't heard of anyone doing it, but maybe it exists.

Switching from 32-bit to 64-bit is generally the same process (and as difficult) as switching to a different Linux distribution. You pretty much preserve your home directory while replacing everything else. I've never tried it, so I can't give you any better instructions.

It is simply not possible. If you have a 64-bit kernel, you need 64-bit drivers, modules and programs. Those are all different from you current installation.

If you do dpkg --get-selections > savefile.txt you are able to install exactly the same packages again after your new installation. If you save your home directory as suggested by someone else, you should be able to retain most of your personal settings. All other custom settings which are stored in /etc are lost unless you have saved them as well.

The benefits of a 64-bits version might be limited. I have the idea it brought me about 10-20% speed increase, but even that is doubted by experts. I can access more than 3GB memory, but I seldom use more than 1GB. However, it gives a warm feeling to run a 64-bit OS on a 64-bit processor, while the system was shipped with 32bits Vista because MS was not able to deliver a stable 64bits version.

I did the switch right after the initial installation on the machines - when I realized that the processor was 64bits and reading the problem reports. Currently the only problem I have is Opera + Flash and that seems to be cross architecture for Opera anyway. Mozilla runs fine.

If you have an installation with a long history, over a few months and the machine is important to you, I would leave it 32 bits and do the 64 bits install on the next machine you buy.

jlinkels