WHAT EXACTLY IS A KERNEL in Software

Draw Denso QR Bar Code in Software WHAT EXACTLY IS A KERNEL

Before we jump into the process of compiling, let s back up a step and make sure you re clear on the concept of what a kernel is and the role it plays in the system Most often, when people say Linux, they are usually referring to a Linux distribution for example, OpenSuSE Linux is a type of Linux distribution As discussed in 1, a distribution comprises everything necessary to get Linux to exist as a functional operating system Distributions make use of code from various open source projects that are independent of Linux; in fact, many of the software packages maintained by these projects are used extensively on other UNIX-like platforms as well The GNU C Compiler, for example, which comes with most Linux distributions, also exists on many other operating systems (probably more systems than most people realize)

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So, then, what does make up the pure definition of Linux The kernel The kernel of any operating system is the core of all the system s software The only thing more fundamental than the kernel is the hardware itself The kernel has many jobs The essence of its work is to abstract the underlying hardware from the software and provide a running environment for application software through system calls Specifically, the environment must handle issues such as networking, disk access, virtual memory, and multitasking a complete list of these tasks would take up an entire chapter in itself! Today s Linux kernel (version 26*) contains almost six million lines of code (including device drivers) By comparison, the sixth edition of UNIX from Bell Labs in 1976 had roughly 9000 lines Figure 9-1 illustrates the kernel s position in a complete system Although the kernel is a small part of a complete Linux distribution, it is by far the most critical element If the kernel fails or crashes, the rest of the system goes with it Happily, Linux can boast its kernel stability Uptimes (the length of time in between reboots) for Linux systems are often expressed in years

(Device Drivers/Virtual Memory/Process Managment)

Hardware (CPU/Memory/Disk)

Your distribution of Linux probably has the source code for the specific kernel version(s) it supports available in one form or another These could be in the form of a compiled binary (*srcrpm), a source rpm (*srpm), or the like If you need to download a different (possibly newer) version than the one that your particular Linux distribution provides, the first place to look for the source code is at the official kernel website: wwwkernelorg This site maintains a listing of web sites mirroring the kernel source, as well as tons of other open source software and general-purpose utilities The main kernelorg site is mirrored around different parts of the world The mirrors are intuitively named using a two-letter country code Although you can connect to any of the mirrors, you ll most likely get the best performance by sticking to your own country or any country closest to you Go to wwwxxkernelorg, where xx is the Internet country code for your country As an example, for the United States, this address is wwwuskernelorg

The web site listing of kernels available will contain folders for v10, v11, v25, v26, and so forth Before you follow your natural inclination to get the latest version, make sure you understand how the Linux kernel versioning system works Because Linux s development model encourages public contributions, the latest version of the kernel must be accessible to everyone, all the time This presents a problem, however: Software that is undergoing significant updates may be unstable and not of production quality To circumvent this problem, early Linux developers adopted a system of using oddnumbered kernels (11, 13, 21, 23, and so on) to indicate a design-and-development cycle Thus, the odd-numbered kernels carry the disclaimer that they may not be stable and should not be used for situations for which reliability is a must These development kernels are typically released at a high rate, since there is so much activity around them new versions of development kernels can be released as often as twice a week! On the other hand, even-numbered kernels (10, 12, 20, 22, 24, 26, and so on) are considered ready-for-production systems They have been allowed to mature under the public s usage (and scrutiny) Unlike development kernels, production kernels are released at a much slower rate and contain mostly bug fixes The version of the kernel that we are going to work with in the following section is version 2627, which is available at wwwkernelorg/pub/linux/kernel/v26/ linux-2627targz TIP You can use the wget utility to quickly download the kernel source into your current working directory by typing