What Is GNU? Exploring Linux’s Core Open‑Source Foundations and Licenses

1. GNU

Linux consists of the kernel and a collection of applications that provide system services and tools. Most of these applications are freely released by programmers under the GNU philosophy, which promotes software freedom and is governed by the GNU General Public License (GPL). GNU, standing for “GNU's Not UNIX,” was launched by the Free Software Foundation founded by Richard Stallman. Its goal is to create a UNIX‑compatible operating system and development environment without the restrictions of proprietary UNIX code.

Key GNU projects released under the GPL include:

GCC – the GNU Compiler Collection, including the GNU C compiler.

G++ – the C++ compiler, part of GCC.

GDB – a source‑level debugger.

GNU make – a free implementation of the UNIX make command.

Bison – a parser generator compatible with UNIX yacc.

bash – the command‑line interpreter (shell).

GNU Emacs – a text editor and development environment.

Other GNU‑licensed software spans spreadsheets, version‑control tools, compilers, interpreters, internet utilities, graphics tools such as GIMP, and full desktop environments like GNOME and KDE.

2. Common Open‑Source Licenses

Mulan License : China’s first open‑source license, covering copyright permission, patent grants, trademark‑free use, distribution limits, and liability disclaimer. It allows contributors to grant perpetual, worldwide, royalty‑free copyright licenses, and is considered more permissive than the Apache License because it does not require listing every modified file.

GPL License : Provides copyright protection and a license for programmers, allowing copying, distribution, and modification of source code while requiring that any derivative work also be released under the GPL. Commercial distribution is permitted if the source and license are provided, but the software cannot be relicensed as proprietary.

LGPL License : Designed for libraries; unlike the GPL, it permits commercial software to link against LGPL libraries without requiring the entire application to be open‑source, though any modifications to the LGPL library itself must remain under LGPL.

BSD License : Offers great freedom to use, modify, and redistribute code, either as open‑source or proprietary. When redistributing source, the original BSD notice must be retained; for binary distributions, the notice must appear in documentation; and the original authors’ names cannot be used for marketing.

3. Summary

This section briefly introduced GNU as a crucial source of Linux applications and outlined several major open‑source licenses, setting the stage for the next section on Linux kernel source structure.