[svlug] Distro kernels

Karsten M. Self kmself at ix.netcom.com
Thu Mar 3 18:25:02 PST 2005

on Wed, Mar 02, 2005 at 10:45:24PM -0800, William R Ward (bill at wards.net) wrote:
> In all this debate about kernels, I'm starting to rethink how I've
> always run my Linux systems.  
> I first started using Linux with the first release of Slackware, 11
> years ago, and later switched to Debian which I continue to use today,
> except for a short flirtation with Red Hat 6.  Through all this time,
> I've always taken the approach of downloading the distro's kernel
> sources and compiled my own, after adjusting various options for
> drivers and features that I needed.

Dittos myself through about 2002.
> Is it time to change, and start using the pre-compiled kernel binaries
> provided by Debian instead?  

I've found it's largely a matter of convenience.

As others have noted, it's also required in some support contexts.

Moreover, I find that the fewer tweaks I make to a system, generally,
the easier it is to maintain.  Debian moots this somewhat through its
make-kpkg tools, under which you compile your own kernel and create your
own customized kernel-image DEB package for installation.

By specifying, though, say:  kernel-image-2.6-<arch>, you'll always be
tracking the most recent stable version of a given kernel image.  Useful
if tracking bugfixes is a concern.

> How do I know which features and drivers are included in the stock
> kernels?  


> And what about the features and drivers I don't need - will they bloat
> my kernel, slowing my system down?

Well, you can benchmark.  Probably not notably, though boots are slower
if you have to load modules.  I find that's a seldom-seen condition
though....  Allowing module loading/unloading does present a security
vulnerability, though IIRC there's a module lock option which can be
used to prevent additional loads after some point in your boot process
(a feature swiped from BSD).

The biggest impact I've seen is that I have to allow for a _lot_ more
space for a stock kernel's modules.  Currently about 40 MiB for 2.6 (2.4
was ~30 MiB).  If you plan on keeping an additional kernel or two around
as you upgrade, that's at _least_ 80 MiB more for your root filesystem,
and if you factor in additional requirements for 2.8, probably well
north of 100 MiB.  While that's not a lot of space relative to current
storage capacities (at least for a desktop -- embedded's another story),
it means my traditionally tidy 80-100 MiB root filesystem partitioning
is simply no longer sufficient.


Karsten M. Self <kmself at ix.netcom.com>        http://kmself.home.netcom.com/
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