Linux 是当今大众媒体中关于自由／开源软件最热门的字眼。但是 Linux 这个词在被广泛使用的同时其含义也越来越宽泛。在关于自由／开源软件的讨论中，了解 Linux 的不同定义是非常重要的。

=作为内核的 Linux=

Linux 最初是 Linus Torvalds 开发的操作系统内核的名字。内核是操作系统的核心部分，它控制中央处理器，管理内存和硬件设备。操作系统内运行的不同程序也需要内核来协调和通信。一些 BSD 版本使用的 Mach 内核也是自由／开源核心中的一种。

核心在某种程度上是可以更换的。大多数自由／开源应用很容易就可以在 Mach 内核，Linux 内核甚至实验性的 GNU Hurd 内核上运行。但是，内核的类型对性能和自由／开源系统硬件平台的兼容性有很大影响。例如，尚不成熟的 GNU Hurd 内核只能在 x86 （PC）架构上运行。Linux 内核已被移植到几乎所有的计算架构上，包括 PlayStation 2 [85]，大型机和嵌入式设备。

=作为发行版的 Linux =

Linux 如今更普遍地用于指称一个内容远不止于内核的 Linux 发行版本。Linux 发行版本（有时被称为 GNU/Linux 以强调 GNU 项目的巨大贡献）包括作为心脏的 Linux 核心以及所有用于实现完整操作系统功能的自由／开源软件组件，包括系统函数库，图形用户界面，各种数据库，网页服务器，email 程序，等等。同样的组件也包含在其他自由／开源的甚至是私有的操作系统中。例如 Linux 和 BSD 缺省的图形服务器 XFree86 也被用于私有的 Unix 系统，如 Solaris，HP-UX 和 IBM 的 AIX 系统。

新闻报道“慕尼黑最终倾向于 Linux”[86] 中的 Linux 是指包括字处理、绘图和 email 软件的发行版本。虽然 Linux 内核二进制文件的长度只占整个 Linux 发行版本的 0.25％，其重要性足以让整个发行版本被称为 Linux。

世界上没有统一的 Linux 发行版本。虽然所有的发行版本都包含 Linux 内核，但它们包括的自由／开源应用软件和配置都各有不同。Linux 有许多商业发行版本，其中一些可以免费获取，还有大量的定制发行版本满足不同用户的独特需求。虽然不同 Linux 发行版本的自由／开源内容大都相同，它们也对从高端服务器到桌面系统甚至嵌入式系统等不同的用途进行了优化。本地化的发行版本至少包括字体、输入法和必要的地区语言菜单翻译。

Linux is the most frequently heard FOSS buzzword in the mass media today. However, because of its common usage, the term Linux has been used to refer to broader and broader definitions. It is important to understand the different definitions of Linux to be able to follow the discussions on FOSS.

Linux as the kernel

Linux was originally the name of the kernel created by Linus Torvalds. A kernel is the critical center point of an operating system that controls CPU usage, memory management and hardware devices. It also mediates communication between the different programs running within the operating system. There are other FOSS kernels, including the Mach kernel that is the core of some of the BSD distributions.

Kernels are to a certain extent interchangeable. Most FOSS applications will run on a Mach kernel, Linux kernel or even the experimental GNU Hurd kernel, without too much difficulty. However, the kernel type greatly influences performance and the hardware platforms that the FOSS system can run on. For instance, the less mature GNU Hurd kernel can run only on the x86 (PC) architecture. The Linux kernel has been ported to run on almost any computing architecture, including the Playstation 2i, mainframes and embedded devices.

Linux as a distribution

The more common usage of Linux today refers to a Linux distribution, which includes far more than the kernel. The Linux distribution (sometimes referred to as the GNU/Linux distribution in recognition of the GNU Project’s significant contribution) contains the Linux kernel at its heart and all the FOSS components required to produce full operating system functionality. This includes the system libraries, GUI, various databases, web servers, email utilities, and others. These same components are also often found on other FOSS and even on proprietary operating systems. For instance, XFree86 is the default GUI foundation in Linux and BSD. XFree86 is also used on proprietary Unix systems such as Solaris, HP-UX and IBM’s AIX system.

Reports that say “Munich May Opt for Linux After All”ii refer to the Linux distribution, including word processing, printing and email software. Even though the Linux kernel forms less than 0.25 percent (binary file size) of a Linux distribution, its functionality is critical enough to allow the entire distribution to be called Linux.

There is no single Linux distribution. While all distributions contain the Linux kernel at its heart, the FOSS applications included and the configurationssupported vary. There are multiple commercial distributions, several freely available, and numerous customized distributions that are targeted to the unique needs of different users. While the FOSS contents of different Linux distributions are mostly identical, they are optimized for different uses such as for high-end servers, user-friendly desktops or even embedded systems. Localized distributions at a minimum include the fonts, input methods and menu translations necessary to use the software in the regional language.