GNU

GNU (German and English [ˈgnuː], listen^{? /i}) is a Unix-like operating system and completely free software developed as a software collection of applications and libraries under the GNU Project, started in 1984. GNU is licensed under the GNU General Public License (GPL). Since the project's own kernel, GNU Hurd, is not suitable for practical use, the system is today usually combined with the Linux kernel and called GNU/Linux, but mostly simply Linux.

The name GNU is a recursive acronym of "GNU's Not Unix" and, to avoid confusion, should be pronounced like the animal gnu in German, not like in English (i.e. not like new). The head of an African wildebeest antelope was also chosen as the logo.

History

After the announcement in 1983 and the subsequent creation of the GNU Project in 1984, which aimed to develop GNU, the GNU operating system has been actively developed ever since. GNU was designed to be as compatible as possible with Unix. There were several reasons for this decision: First, it was certain that most companies would reject a fundamentally new operating system if the programs they used would not run on it. On the other hand, the architecture of Unix allowed for fast, easy, and distributed development, since Unix consists of many small programs, most of which can be developed independently.

In 1990, a development system with the GNU C compiler and many system programs was ready, but a kernel was still missing. The Free Software Foundation then decided (after much back and forth) to use the Mach kernel. Based on this, a multiserver operating system was to be written so that the system could be extended more easily by further components and users without administrator rights could also integrate their own components without endangering the stability of the overall system.

The multiserver system was christened GNU Hurd. However, since it made heavy use of multithreading, debugging proved to be very difficult. The project became very large and difficult to manage. At the same time, developers were drawn to the much more pragmatically developed Linux, thus missing GNU Mach and GNU Hurd. The development of these parts was slow. During this time, a running gag developed where users would ask when Hurd would be ready, and the answer would refer to the respective next year. Hurd is therefore often referred to as vaporware.

In 1998, Marcus Brinkmann started the Debian GNU/Hurd project to give development more momentum again. The infrastructure of the Debian project was made usable for GNU Mach and GNU Hurd, allowing a larger number of applications to be ported to the system for the first time. A usable installation routine was created as part of Debian GNU/Hurd, also X11, Gnome and KDE were ported to the platform. In addition, it benefited from the mature package management using apt-get, dpkg, and the other tools Debian provides for system management. Brinkmann also extended GNU Hurd with a Unicode-enabled console that is based on a client/server architecture and thus clearly surpasses the Linux console in flexibility.

In 2001 there were also efforts to port GNU Hurd from the Mach microkernel GNU Mach to an L4 kernel, a second generation microkernel. This L4 Hurd project, like Debian GNU/Hurd, was also significantly driven and coordinated by Marcus Brinkmann. In February 2005 the first phase of this port was finished. First small programs can be executed under a GNU-Hurd-L4 system since then. However, neither a shell nor the GNU software is available yet, so interaction with the system is limited to using the kernel debugger for the time being. In January 2006 there were considerations to use Coyotos instead of the L4 microkernel.

Kernel

The GNU Project envisions the GNU Hurd kernel for GNU. The decision for this experimental kernel was an important reason for the stagnant development of a usable GNU operating system.

GNU Mach is the GNU Project's favored microkernel for hardware abstraction. It is an implementation of the Mach kernel and currently (as of December 2015) the default microkernel of GNU Hurd. GNU Mach so far only runs on machines of the deprecated Intel 32-bit architecture. More ports are planned for the future, though development is stagnating. Since the combination of Mach and Hurd is thus still difficult to use productively, Linux is very often used as the kernel and the entire system is just called "Linux" instead of GNU/Linux.

"Hurd/L4" or "L4-Hurd" is a project that was supposed to port "GNU Hurd" to the L4 microkernel and thus replace GNU Mach in the long run. However, L4 has turned out to be unsuitable.