Downgrading a 2.6 Kernel to 2.4
 

I'm sorry for asking such a simple question (and the fact that I haven't been on LQ since like forever doesn't help either).

A couple of months ago, I designed an openMosix cluster running RedHat 9 and openMosix 2.4.26-openmosix1. Everything worked very well in RedHat 9. There are 4 nodes (more on the way), one of them being the master.

But after gettting bored (famous last words?) with RedHat, I decided to move to something faster, more powerful, etc. Well, I don't know if I actually achieved that, but I went to SUSE 9.1 because of its excellent support for hardware and its integrated environment. I installed all of the packages from a mirror server ;).

Anyways, as you may know, SUSE 9.1 uses a 2.6 kernel (2.6.5-7.201 for me). The support for the 2.6 kernel in openMosix, however, is very weak, and I don't wish to use it.

So, I'd like to downgrade to a 2.4 kernel (2.4.26 to be exact). This is going to be quite a job, I know, but if I can do so, I can have openMosix running very well.

I found a similar topic at http://www.linuxquestions.org/questi...hreadid=370254, but it didn't really give any information.

I've had very bad experiences in building kernels in the past (i.e. if I didn't use make oldconfig, I'd be getting all sorts of problems with OS integration). Building one from a source RPM with openMosix patched in was scary enough. However, it is pretty much imperative now that I run the 2.4.26-openmosix1 kernel for my cluster.

So, I'd greatly appreciate it if someone could give me a brief explanation of things that could go wrong, things that won't work because of the downgrade (I heard ALSA isn't going to work properly among other things), and any tips for some automatic configuration of the kernel would also be great.

Thanks so much.

To automate kernel configuration and compilation, you should investigate buildkernel. I've used it some years back with CalderaSystems OpenLinux (worked very well because the OpenLinux kernel compile was quite straightforward). I haven't tried it yet with SuSE 9.3 (the kernel compile is much more complex because of SuSE's way of doing things).

Anyhow, with buildkernel, you can build several versions of the same kernel, each with it's own /lib/modules (to prevent conflicts between versions). Setting it up to build a 2.4 kernel should not be a problem.

Note: buildkernel also has an option in the script to add a patch file to the compilation (you move/copy the patch to the SOURCES directory and proceed with compilation. If the script knows about the patch, it will apply the patch during compilation).

After the kernel compilation, what problems could you run into? To start with, software applications compiled for the capabilities of the 2.6 kernel: all would have to be recompiled for the 2.4, unless you have software which didn't change much between the two kernel releases.

Is that a steep enough hill to climb?

I'll look into buildkernel, thanks for the tip.

Generally, when I've rebuilt kernels in the past (on Slackware among other distributions), I run into all kinds of errors involving modules. I can't recall them off the top of my head, but they usually have been symbol loading errors, incorrect module errors, etc.

Considering how much software that I have installed on the system, I'm quite weary of recompiling everything for a 2.4 kernel. I'm wondering if I should just wait until full support for 2.6 comes out yet. When you have installed about 10gB of software, it's kind of hard to see what you'll need to recompile. Plus, I'll be pretty much on my own with installing and configuring things and so forth, and that's precisely what I wanted to get away from. So right now, I'm thinking installations of Redhat and SUSE. Plus, that gives me another reason to buy a new hard drive :). In that time, I'll wait for the 2.6 support to come out.

Thanks for you help and I do intend to look into buildkernel soon for some other purposes that I have.

While I am "morbidly intrigued" by what it is that would motivate you to downgrade your system to an earlier kernel, you can certainly do that if you wish. The key will be to make sure that any other parts of your system which may be reliant upon the availability of 2.6 services (such as, particularly, your all-important glibc library) will continue to run successfully in an earlier environment.

In any case, you can download a 2.4 kernel, compile it, install it, and boot from it. All other things being equal, your present system will now be running (or, attempting to do so) with a 2.4 kernel. Either it will work successfully or it will not... in which case you can reboot and select your previous kernel.

I am still, however, "morbidly intrigued" by what, exactly, causes a dependency upon an earlier version of the Linux kernel. As far as I am aware, very few applications speak directly to the kernel at all... they interact with a library such as glibc, which in turn issues kernel-level calls.

When you deal with "the kernel," bear in mind that loadable modules are part-and-parcel of "the kernel!" When a kernel-module is loaded, it becomes a full-fledged part of the kernel... as though it had been compiled-in from the start. You cannot mix the two: you can't use a 2.6 kernel-module with a 2.4 kernel or vice-versa.

Offhand, I would suggest that you begin by staying precisely where you are, and contact the vendor/supplier of openMosix for advice. "Follow the leader" and do exactly what they advise. If they are working on 2.6 support but don't have it ready yet, then install the latest 2.4-based distro you can find. The overarching concern for you is that "you have in your possession 'a system that will run openMosix reliably.'" Period, end-of-sentence. Don't try to carve out new territory here... ask them, and follow their advice.

There is a patch for the 2.6 kernel, just without automatic migration of processes. It is supposedly still in development, but the last bit of news over at http://openmosix.sourceforge.net/ was from July and the community seems to be somewhat dead. I can't really tell what's going on over there. I'll try emailing someone.

I'm looking at OSCAR right now; it might be my temporary choice while I wait for 2.6 support to come out.