http://groups.google.com/groups?selm=8ufpoa%24aoe%241%40iac5.navix.net

Newsgroups: comp.os.linux.setup, comp.os.linux.misc
Date: 2000-11-07 12:01:39 PST

> I installed RH 7.0, however I want to have this drive as a primary slave
> to my NT install which is on the primary master.  When I use the boot
> disk it gives a kernel panic cannot mount 3:20 or something....

I ran into this problem several times before I finally figured out what was happening. I was using a different distribution, but that's not part of the issue.

When a kernel is created, it has some default values built into it. The kernel can be loaded several different ways. One way is to write it in binary mode to a floppy diskette. Another is to use a boot loader. The boot loader allows you to choose what partition you are going to boot and, if it's a good boot loader, like "lilo", will also allow you to pass override parameters to the kernel.

Regardless of how the kernel is loaded, it has to know what device has the root file system on it. Linux, like all *nix, has a single-rooted file heirarchy. In DOS, you have drive A:, B:, … Z: each of which has its own root directory.

In Linux, there's only one "root directory". It's on the root device. Various physical disks are grafted into a directory tree at mount points. But the tree has to have a root somewhere. What's happening with the kernel panic, is that the kernel is getting loaded from the floppy, and it thinks the root directory (root device) is supposed to be /dev/hda20 (3:20 = hda20?). When the kernel goes out to mount the root file system, it doesn't find the root file system (root directory) it wants and it goes into a "panic".

What you need to do now is to override the default setting in the kernel so that it expects to find the root file system on the actual device where you installed the root file system. Either that, or you need to use a boot loader that allows you to pass parameters to the kernel. Kernel parameters passed this way will override the default parameters in the kernel. You can tell your boot loader to ignore the root device pointed to by the kernel, and to use the file system on /dev/hdb5. It will be quite happy. Or you can boot with a kernel that has /dev/hdb5 set for its default.

I don't know much about NT, but from what I've read, you can use NT loader to boot Linux as well as NT. That would allow you to have a boot menu started from the hard drive. Pretty nice, useable solution. To make it work smoothest, modify the kernel to look for the root file system on /dev/hdb5. That doesn't take a recompile. There's a utility called "rdev" that changes the root device pointer in the kernel. There are a couple other items you can change in the kernel using this utility, so I recommend you use "man rdev" to get the low-down on it.

Once you've used rdev to modify the root device pointer in the kernel, you won't get kernel panic anymore. You will also want to consider swapdev, etc. ("man rdev" explains this) and the other kernel settings. With the proper minor adjustments, you will be able to boot using any of the popular methods. (NT boot loader, floppy with raw kernel, floppy with lilo, OS2 loader, loadlin, …)

If you like booting from a floppy, you might consider installing just the lilo boot loader on the floppy. It takes only a second to load. Much faster than the 10-20 seconds it takes to load the entire kernel from a floppy.

Gene Wiggins

: from the floppy, and it thinks the root directory (root device) is
: supposed to be /dev/hda20 (3:20 = hda20?).  When the kernel goes out

: I don't know much about NT, but from what I've read, you can use
: NT loader to boot Linux as well as NT. That would allow you to have

: the root file system on /dev/hdb5.  That doesn't take a recompile.
: There's a utility called "rdev" that changes the root device