LinuxSea：Gentoo Linux 操作系统入门指南

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Chapter 1. What is Linux?

running processes, ...), privilege related tasks (changing ownership of ﬁles, changing user ids, updating

ﬁle permissions, ...) and more.

If you don’t know how to deal with all this stuff, you don’t know how to work with your operating

system. Some operating systems hide these tasks behind complex tools, others have simple tools for each

task and bundle the power of all these tools. Unix (and Linux) is one of the latter. Linux systems usually

have the GNU Core Utilities for most of these tasks.

1.2.4. Development Tools

With the above three components you have a running, working operating system. You might not be able

to do everything you want, but you can update your system until it does what you want. How? By

installing additional tools and libraries until you have your functional system.

These additional tools and libraries are of course written by programmers and they must be able to build

their code so that it works on your system. Some systems, like Gentoo Linux, even build this software for

you instead of relying on the prebuilt software by others. To be able to build these tools, you need the

source code of each tool and the necessary tools to convert the source code to executable ﬁles.

These tools are called a tool chain: a set of tools that are used as in a chain in order to produce a working

application. A general tool chain consists out of a text editor (to write the code in), compiler (to convert

code to machine-speciﬁc language), linker (to combine machine-code of several sources - including

prebuilt "shared" libraries - into a single, executable ﬁle) and libraries (those I just mentioned as being

"shared" libraries).

A tool chain is of the utmost importance for a developer; it is a vital development tool, but not the only

development tool. For instance, developers of graphical applications generally need tools to create

graphics as well, or even multimedia-related tools to add sound effects to their program. A development

tool is a general noun for a tool that a developer would need in order to create something, but isn’t vital

for an operating system of an average non-developer user.

The most well-known development tools are also delivered by the GNU foundation, namely the GNU

Compiler Collection, also known as gcc.

1.2.5. End User Tools

Once a developer has ﬁnished creating its product, you have an end-user tool with accompanying

libraries (which might be required by other tools that are build on top of this product). These end tools

are what makes a system unique for a user: they represent what a user wants to do with his system.

Although not required by an operating system they are required by the end user and are therefore very

important for his system.

Chapter 1. What is Linux?

Most operating systems don’t install all or most of the end-user tools because there are just too many to

choose from. Some operating systems don’t even provide the means to install end-user tools to their users

but rely on the ingenuity of each programmer to create an installer that sets up the tool on the system.

Other operating systems bring a small but considerable subset of end-user tools with them so that their

users can quickly update their system to whatever shape they want without requiring a long and difﬁcult

search across the Internet (or even worse, computer/software shop) to ﬁnd the software they need.

Examples of end-user tools are well known, such as ofﬁce suites, graphic design tools, multimedia

players, communication software, Internet browsers, ...

1.2.6. Okay, I bite, What is this GNU?

The GNU Project is an effort of several programmers and developers to create a free, Unix-like operating

system. GNU is a recursive acronym that stands for GNU is Not Unix, because it is Unix-like but

contains no Unix code and is (and remains) free. The GNU foundation, the legal entity behind the GNU

project, sees free as more than just the ﬁnancial meaning of free: the software should be free to use for

any purpose whatsoever, free to study and modify the source code and behaviour, free to copy and free to

distribute the changes you made.

This idea of free software is a noble thought that is active in many programmers’ minds: hence many

software titles are freely available. Software is generally accompanied by a license that explains what

you can and cannot do with it (also known as the "End User License Agreement"). Free Software also

has such a license - unlike the EULAs they actually allow most things instead of denying it. An example

of such license is the GPL - GNU General Public License.

1.3. Linux as the Kernel of the Linux Operating System

When we look at a Linux Operating System, its core component is its kernel. The kernel all Linux

Operating System use is the Linux kernel, or just Linux. Yes, that’s right, the Linux Operating System is

called after the kernel, Linux.

Now although all Linux Operating Systems use Linux as their kernel, many of them use a different

ﬂavour. This is because the kernel development has several branches. The most important one I call the

vanilla kernel. This kernel is the main development kernel where most kernel developers work on; every

other kernel is based on this kernel. Other kernels introduce features that the vanilla kernel doesn’t want

yet (or has tossed away in favour of another feature); still, these kernels are fully compatible with the

vanilla kernel.

The Linux kernel saw its ﬁrst light in 1991 and is created (and still maintained) by Linus Torvalds. It

grew rapidly (in 1994, version 1.0.0 saw the light) both in size (1.0.0 had more than 175000 lines of

code) and in popularity. Over the years, its development model stayed the same: there are few major

Chapter 1. What is Linux?

players in the development who decide what goes in and what stays out of the kernel code, but the

majority of contributions happen from several hundreds of developers (kernel 4.8 had contributions from

more than 1500 individuals).

The latest kernel version at the time of writing is 4.8.15. The ﬁrst two numbers play the role of the major

version, the third number is the minor version (mostly bugﬁx releases). Sometimes a fourth number is

added when a one-off bug ﬁx was needed. The Linux kernel development generally increments the major

numbers (most of the time the second number) for functional improvement releases: for every increment,

users (and developers) know that the kernel has new features.

Once a new version of the Linux kernel is released, it isn’t distributed to all of its users. No, this is where

distributions come into play...

1.4. Linux Operating Systems: Distributions

If an end user would want to install a Linux Operating System without additional help, he would need to

build a Linux kernel himself, build the components of the operating system (like the libraries, end tools

...) and keep track of changes in the free software world (like new versions or security ﬁxes). And

although all this is perfectly possible (look for the Linux From Scratch project), most users would want

something that is a bit more... user friendly.

Enter distributions. A distribution project (like the Gentoo Project) is responsible for a Linux Operating

System (the distribution) to such an extend that for the end user, the distribution project is the point of

contact for his Linux installation.

Distribution projects make choices regarding the software:

•

How should the users install the operating system?

Perhaps users are encouraged to perform as many steps as possible during the installation process (the

"distribution" Linux from Scratch probably has the most intensive installation process). The very

inverse is an installation CD or USB image that doesn’t even require any conﬁguration or installation:

it just boots the environment and you’re ready to start using the Linux distribution.

•

What installation options are there (CD, DVD, network, Internet, ... ?)

Chapter 1. What is Linux?

Most Linux distributions offer an installation CD/DVD as it is the most popular method for acquiring

software. But many other installation options exist. You can install a distribution from a network using

net booting (a popular approach in enterprise environments as it makes unattended installations

possible) or from within another operating system.

•

What software should be available to the user?

Popular desktop Linux distributions offer a wide range of software to the end users. This allows the

distribution to become widely accepted as it ﬁts the needs of many users. However, more advanced

distributions exist that focus on a particular market (like set-top boxes for multimedia presentations,

ﬁrewalls and network management, home automation appliances, ...) and of course, these distributions

offer different software titles to the users.

•

How is the available software built (speciﬁc system, features ...)?

If a distribution wants the software to run on as many processor types as possible (Pentium, i7, Athlon,

Xeon, Itanium, ...) it needs to build the software for a generic platform (say i686) rather than for a

speciﬁc one (Itanium). Of course, this means that the software doesn’t use all features that new

processors provide, but the software does run on many more systems.

The same is true for features supported by certain software titles. Some software titles offer optional

support for ipv6, ssl, truetype fonts, ... but if you want it, you need to compile this support in the

application. Distributions that offer software in a binary format (most distributions do) need to make

this choice for their users. More than often, they attempt to offer support for as many features as

possible, but not all end-users would need or even want this.

•

Is internationalization of the software important?

Some distributions are targeting speciﬁc user groups tied to their language and geography. There are

distributions that are fully localized to a speciﬁc group (say "Belgian Dutch-speaking users" or

"Canadian French-speaking users"), but also distributions that try to offer localization for as many

groups as possible.

•

How should users update and maintain their system?

Chapter 1. What is Linux?

Many distributions offer an automated software update process, but not all distributions offer a live

upgrade process (where, once installed, your installation gradually builds up and becomes the latest

version of that distribution without any speciﬁc actions). Some distributions even require you to boot

from the latest installation CD and perform an upgrade step.

•

How would a user conﬁgure his system?

If you are a graphical Linux user, you deﬁnitely don’t want to hear about conﬁguration ﬁle editing or

command-line actions to be taken. So, you will most likely look for distributions that offer a full

graphical interface to conﬁgure your system. But some users do like the idea of writing the

conﬁguration ﬁles directly as it offers the largest ﬂexibility (but also the highest learning curve) and

distributions often work on these sentiments. Some distributions don’t even allow you to update the

conﬁguration ﬁles directly as they (re)generate those ﬁles anyway (overwriting your changes).

•

What is the target user group of the distribution?

Most desktop distributions target home/ofﬁce users, but there are distributions that target children or

scientists. Some distributions are made for developers and others for elder people. There are

distributions for visually impaired people and distributions for people without Internet access.

•

What policies does the distribution put on its software?

Organizations like FSF have a vision on how the (software) world should look like. Many distributions

offer a way of implementing these visions. For instance, some distributions only allow software that is

licensed under an FSF-approved license. Other distributions allow users to use non-free software.

There are distributions that implement a higher security vision in the distribution, offering a more

hardened approach to operating systems.

•

Should the distribution be freely available?

Of course, money is often a major decision point as well. Not all distributions are freely downloadable

/ available on the Internet, although the majority is. But even when the distribution is freely available,

it might still be necessary to obtain commercial support, even just for the security updates of the

distribution.

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