[Beowulf] cloning issue, hidden module dependency

Tim Cutts tjrc at sanger.ac.uk
Tue Dec 9 01:07:14 PST 2008

On 8 Dec 2008, at 11:15 pm, David Mathog wrote:

> Bogdan Costescu wrote:
>> Having a monolithic kernel that "just works" on a large variety of
>> hardware means answering "y" to most drivers; the kernel itself would
>> then grow as large as the "immense initrd" that you mention.
> I don't think so. It only has to work with a large variety of disks,  
> and
> at that, not necessarily at optimal speeds.  Basically it just has to
> function well enough to access the OS files on disk, where the rest of
> the modules are, so that those drivers can be loaded later.  The boot
> kernel need not have every video, network, etc. driver in it.
> In any case, the sizes of the vmlinuz/initrd files discussed so far
> are:
> Distro            Kernel     vmlinuz  initrd Kernel has IDE builtin
> Mandriva 2007.1  (  1607583  357892   Y
> Mandriva 2008.1  (  1787352 2214302   N
> Ubuntu 8.04.1    ( 1903448 7906356   N
> Sure this is apples and oranges, but to me it looks like taking the  
> stuff (and maybe other drivers) out of the boot kernel is resulting
> in larger and larger initrd files, with the size of initrd going up
> faster than the size of vmlinuz, by a lot.

Ubuntu put quite a lot of other stuff into the initrd which has  
nothing to do with device drivers.  For example, the initrd includes  
casper and all its support scripts, which provide support for things  
like persistent USB storage when running as a Live CD.

But they also do put the entire kitchen sink in there in terms of  
device drivers; Ubuntu does aim to cover as wide as possible a range  
of possible hardware.  It's very easy to build a custom kernel package  
with just what you want using the 'make-kpkg' command, and then you  
can strip out all the extraneous cruft if you want (I never bother -  
it's only modules that don't get loaded, and the only performance  
issue would be if you're PXE booting)


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