Re: Using Lilo to select different Kernels
"Doug MacFarlane" <madmac@covad.net> writes:
[snip]
> I'm in the process of learning to compile my own kernels, and since
> I do everything the Debian way, i'll be a kpkg guy and build .debs
> of my custom kernels, which will install in identical fashion, as
> the prepackaged kernels.
make-kpkg is a *very* nice piece of software. Makes maintaining your
own kernels relatively painless.
> That said, as near as I can tell from looking in /boot, when one
> installe a kernel in this fashion, everything is still there from
> the previous kernel except the symlink from vmlinuz to the kernel or
> initrd image, so . . .
Actually, I think the default behavior for Debian is to set up
/etc/lilo.conf to keep two kernels in the boot menu. The current one
you just installed and the old one. This is done using the links
/vmlinuz and /vmlinuz.old. So if you were running 2.2.20 (from a
default Debian install) and then installed a prepackaged
kernel-image-2.4.19 the new kernel package would likely have reset
/vmlinuz.old to point to /boot/vmlinuz-2.2.20 and set /vmlinuz to
point to /boot/vmlinuz-2.4.19 and if you let the package script run
lilo for you, and assuming you have a default /etc/lilo.conf file, you
can boot either of those two kernels from the LILO prompt. For a new
install, of stable, I think your choices are Linux and LinuxOLD. Of
course you can hit TAB (I think) at the LILO prompt and it'll give you
the list of possibilities.
> Is it possible to have multiple LILO entries to boot different
> kernels off of the same /boot partition?
My replay above should give you a hint. Yes, you can have as many
kernels, of different kernel versions (like 2.2.20, 2.4.18, 2.4.19,
etc.), as you want. If you want different kernels of the same kernel
version, i.e., you want to install multiple copies of the 2.4.19
kernel, you'll have to look at kernel "flavors" (--append_to_version
in newer make-kpkg speak) I believe. Otherwise it will install over
any previous kernel of the same kernel version.
If you want to have more than two kernels in LILO you'll probably have
to set that up yourself by editing /etc/lilo.conf. It'd be easy to do
by just copying the already existing Linux and LinuxOLD sections and
replacing the appropriate fields to coincide with your kernel,
including specifying the kernel image in /boot.
> And as a followup, what's the difference between booting a kernel,
> and booting an initrd image? Why have the prepackaged kernels moved
> to initrd? Why would I want to build my custom kernels to boot as
> initrd images? Why wouldn't I?
initrd allows pretty much any and all drivers to be built as
modules. The bare-bones kernel is then booted, via initrd, and it
loads the modules necessary to continue booting your computer, for
example your disk controller (IDE, SCSI). This allows you to build a
single generic kernel that will boot on pretty much any hardware
supported by Linux. In contrast, distributions used to have to build
kernels for different drivers. You'd have kernels like
kernel-image-2.2.x-idepci, kernel-image-2.2.x-scsi, etc., so that you
could install on a specific computer with the specified hardware. They
had to do this because building all the necessary drivers into the
kernel, so that you could boot on any conceivable hardware, made the
kernel too big to fit in memory at boot time.
I, personally, don't like using initrd for my own custom kernels. Just
adds another layer to the boot process that I'd rather avoid. Since
you, in theory, know what you need to compile into your own custom
kernel in order to boot your machine you shouldn't need to use
initrd. Now if you were maintaining a custom kernel for a large
variety of machines it might be worth it so that you could avoid
compiling custom kernels for each machine, but that's the only reason
I am aware of for using initrd for custom kernels.
All of this is to the best of my understanding, and I'm hardly an
expert on initrd since I don't use it, so take it with a grain of
salt.
Gary
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