linux Kernel

[Kent Borg]

On Sat, Oct 28, 2006 at 10:48:27PM +0530, Cheatah 0#@!^ wrote:
> What is the real concept of a linux kernel ? What all are the
> constituents if it ?

The Linux kernel is a single computer program, it isn't very big, when
compressed it is less than 2 megabytes.  There are additional files
that hold "modules" that know how to talk to specific pieces of
hardware, but when the needed modules are loaded into the kernel it is
still pretty much just one program.

So when a Linux computer boots, it runs the kernel, and the kernel
keeps running until the computer shuts down.  The kernel is *the*
program that is always running.  The kernel, in turn, runs other
programs, and parcels out access to CPU time so those programs can
run.  When a program wants to access some hardware, it has to go
through the kernel, when a program wants some RAM, it has to ask the
kernel for that RAM.  And when a program quits (or crashes), if it
doesn't clean up after itself (returning used RAM, closing hardware
drives, etc.), the kernel does that cleanup.

On Ubuntu the kernel is usually in /boot, and is called something like
vmlinuz-2.6.15-27-686.  In this case the corresponding modules are
located in /lib/modules/2.6.15-27-686.

When people say "Linux" they usually mean a lot more than just the
kernel (gigabytes more these days), and there is plenty of other stuff
that happens.  For example, the first program that the kernel runs is
usually "init", it also keeps running as long as the computer runs,
and it runs other programs...and the whole cascade is complicated.
[In fact, Ubuntu actually mounts a RAM disk (on my computer it is
stored in /boot/initrd.img-2.6.15-27-686) and does sort of a pre-boot
from there, that gets things ready for the real copy of init to load.
For example, init might be sitting on a disk that can't be accessed
until a module is loaded that knows how to access that kind of disk.]

> Are all the folder which we see in the "/"(root folder) the
> constituents of a kernel, or is it a single file ??

/root is the home directory for the root user (a user that you never
want to login is as).  Nothing crucial for Linux operation is kept in
/root.


-kb, the Kent who gets behind in reading his mailing list messages.