Architecture of the GNU / Linux

[LinuxScho]

As with any operating system, Linux kernel is an interface between programs and hardware devices. Access to these devices is done via system calls that are identical regardless of the machine. This encapsulation material frees software developers to manage complex devices: the operating system that does that. Thus, if the operating system exists on multiple architectures, user interface and programming will be the same on all. We shall then say that the operating system provides a virtual machine to the user and the programs it runs.

GNU / Linux is considered a monolithic operating system, written as a set of procedures that can call each other. To the user it appears as one large file. However, it contains a set of components each performing a specific task. This monolithic construction induces an important aspect: the concept of kernel space (kernel space) and user space (userspace). In kernel space, no restrictions are imposed. In user space, a number of restrictions are imposed (eg, the creation of a file can not be achieved unless the rights are sufficient), and the process can only access memory areas that have been allocated. The Linux kernel is composed of five major subsystems. A subsystem can be defined as a software entity that provides a particular feature.

[LinuxScho]

Subsequently, many implementations of UNIX were developed. The University of Berkeley was at the base of the BSD version, Hewlett Packard offers the HP-UX, etc. ... Despite good intentions were, there were inconsistencies between these Unix, so that porting an application from one UNIX to another was difficult. To reduce these disparities, the AT & T proposed a standard UNIX in 1983, known as System V. In 1986, the Institute of Electrical and Electronics Engineers (IEEE) proposed another standard known as POSIX. POSIX is a standardization to ensure the portability of applications from one UNIX to another. The operating system Linux behaves like a UNIX and implements the POSIX specification, with extensions System V and BSD.

[RogerFielden]

• Process Management, Scheduler, Scheduler : This subsystem is responsible for equitable distribution of access between the processor all running applications. This process includes not only users but also the subsystems of the kernel itself. This function is performed by the Scheduler.
  
• Memory management : This subsystem is responsible for assigning each program a memory area. It also has a protective role: the memory for a process is private and it should not be read or altered by another.
  
• Virtual File System : The sub-file system ensures proper management of files and control access rights. To reduce the complexity associated with many existing file systems, Linux adopts the concept of Virtual Filesystem (VFS). The principle is to provide the VFS system calls identical regardless of the file system. It is the responsibility of the core standards to divert calls to specific calls to the file system.

[Rebella]

All GNU / Linux distributions provide the kernel sources at the same time as compiled versions. The aim is to cover distributions maximum hardware configurations. For this reason, there is a tremendous amount of modules with the nuclei come with distributions. Linux kernel packages come with the Debian GNU / Linux include the list of configuration options selected. This list is available as a text file sources. For example, if we identify the kernel related packages installed on a Linux system as follows:

 $ Dpkg-l linux-image * | 
grep ^ ii ii linux-image-2.6-amd64 2.6.26 16 
Linux 2.6 image is AMD64 ii linux-image-2.6.26-1-amd64 2.6.26-8 
Linux 2.6. 26 image is AMD64

In this case, the package linux-image-2.6.26-1-amd64 contains the file /boot/config-2.6.26-1-amd64 in which we find all the options chosen to build it. Without prior handling, these are the options in this file that will be used to compile a new kernel from source. This solution is beneficial for beginners because it can not change that part of the options a functional configuration set.

[Christina 80]

The solution can compose a core exactly suited to its hardware configuration. Thus, use of the resources of the computer. However, it must know very precisely the components of the machine to configure. This is the second solution: download the kernel source and compile manually, which is retained for the remainder of the presentation. The main site of release of the Linux kernel source is called The Linux Kernel Archives. It provides a list of different kernel versions active a list of mirror sites. The cores are available in tarball format. This format is actually a large file archive created with tar that contains all the source tree into a single file. There are 2 types of downloadable files that are distinguished by the compression tool used.

• Files of type linux-2.6.xx.tar.gz have been compressed with gzip.
  
• Files of type linux-2.6.xx.tar.bz2 have been compressed with the bzip2 compression utility.

In both cases, decompression is performed using the same command. Here's an example:

$ Cd / usr / src /
 $ Tar xf linux-2.6.xx.tar.bz2

[Lawford]

In the usual hierarchy of the GNU / Linux, the source storage directory is: /usr/src . This directory is writable to the group src . So from a user account belonging to that group that is running the following list of commands "ritual" after downloading the kernel sources. In this example, the characters xx are to replace the current version of the kernel.

$ Mv linux-2.6.xx.tar.bz2 / usr / src 
 $ Cd / usr / src
 $ Tar xf linux-2.6.xx.tar.bz2 
 $ Ln-sf linux-2.6.x linux 
 $ Cd linux

• Extracting the kernel source tree.
• It is possible to maintain multiple source trees LINUX kernel. We then use a symlink linux to the directory tree work.

[Acalapati]

It has three different user interfaces to configure a kernel: text mode, text mode with menus and graphics mode. As in manipulation presented above, we assume that the normal user account is part of the systems src and it has write permissions on the directory tree /usr/src/. The text is limited to minimum hardware and nostalgic VT100 consoles. It is not very convenient to use.

$ Pwd
 / Usr / src / linux
 $ Make config

The text mode menu is very convenient for handling on remote servers without a GUI or a screen or keyboard. Generally, the configuration operations are done via a console ssh secure with the tool. It is necessary that the package ncurses development libraries installed on the system where it performs the configuration. We make sure you install the package with a command like:

dpkg-l libncurses *- dev | grep ^ ii.