Messaging Solutions in a Linux Environment

Chapter 1. Introduction to Linux and messaging 3

Similarly, when we talk about versions of Linux we either mean the version of the

Linux kernel or a version of a specific Linux distribution. It is more accurate to talk

about Linux kernel version 2.4 and Red Hat Enterprise Linux version 3 than to

refer to Linux 2.4 or Linux 3.

1.1.2 Linux kernel

The Linux kernel has a monolithic design, which means that most of the

operating system is a single file that runs in

kernel mode, other examples of such

operating systems are DOS, UNIX and VMS. The binary contains:

򐂰 Low-level hardware support for devices such as the processor, interrupt

controller, real-time clock, input devices, CD-ROM drives and so on

򐂰 Memory management

򐂰 Task management and task scheduling

򐂰 Networking protocols such as TCP/IP and Netbios

򐂰 Bus support for PCI, ISA, MCA, USB, FireWire

򐂰 File system support.

򐂰 System call interface, a layer between the kernel and the programs running

on top of it, and its implementation

򐂰 Device driver management

򐂰 Device drivers themselves, which are interacted with by programs through

device specific files, such as SCSI and IDE disk drivers

򐂰 Power management

In order to better understand Linux kernel and its constant development, let us

become familiar with some definitions:

Linux kernel mailing list A virtual space where Linux developers from

around the world discuss the kernel features,

exchange experience, ask questions and help

each other

Bitkeeper repository A source control system used for the official, and

many of the unofficial, development trees

Patch A new kernel feature or modification of an

existing one, sometimes a temporary fix for a

bug until the problem can be solved more

thoroughly with an architectural change

Patch set A collection of patches against an official kernel

release with a certain purpose, such as

4 Messaging Solutions in a Linux Environment

additional experimental drivers, low latency for

enhanced desktop interaction, and so on.

Kernel release A new official kernel level that has been tested

to be stable. In every new version or release

there are improvements or changes to already

implemented architectures and support for new

emerging technologies and optionally for old

obsolete technologies

Custom kernel Some of the major distributions and many Linux

users create their own kernels adding and

deleting features in order to create a kernel best

fit for the additional programs they ship.

Changelog A list of changes and new features compared to

the previous official release.

As an example, we can examine the latest stable Linux kernel, 2.6.5, and its

development process:

1. Developers around the world are fixing bugs and writing new features or

polishing up ones that had not previously been accepted to be included in the

official kernel.

2. All these

patches and patch sets are submitted to Linus Torvalds himself who

works on the

Linus development tree on Bitkeeper together with a few other

trusted associates.

3. Linus himself made the decision which

patches are going to be included in the

new stable kernel.

4. At some point in time, Linus decides to cut off the patch submission process,

effectively freezing the functionality, and releases a

release candidate version.

There may be several of such versions.

5. When the new functionality is tested to a satisfactory degree, the new

kernel

is officially released; announcement is made and source tree together with

changelog is made available at Linux Kernel Archives and its mirrors all

around the world. Many developers who like to follow the

bleeding edge

immediately download the kernel and compile it to take advantage of the new

features it offers. On the Web the Linux kernel archives is found at:

http://www.kernel.org/

6. Major changes and additions according to the changelog in this kernel

include:

– Updates to several file systems including reiserFS, nfs, ext2 and ext3.

– Addition of Netpoll interface.