Linux is a popular, open-source and free OS that consists primarily of a kernel and a set of GNU utilities. Linux is used as a server OS for shared servers (i.e. web servers, database servers and email servers). It is also widely used on home and enterprise desktops, as well as on smartphones and tablets.
The kernel is the core of an operating system. It controls access to various computer resources and acts as an interface between software and hardware. There are five main types of kernels: monolithic, microkernel, nanokernel, hybrid kernel, and exokernel.
Some kernels have been developed for a specific operating system, as is the case for Microsoft Windows 2000 and Microsoft Windows 98. By contrast, there are many versions of the Linux kernel, which can be modified and configured by users.
The kernels used by Unix-like operating systems, such as Linux, are called monolithic. Despite some disadvantages being pointed out, such as the fact that an error in the kernel could cause the system to crash, or that they are not portable, or that the source code could become very large, supporters claim that they are easier to design correctly and quicker to improve.
On a Ubuntu 20.04 distribution, you can find the Linux kernel in this location:
ls -l /boot
The GNU Project
“GNU is a collection of free software which can be used as an operating system or can be used in parts with other operating systems.” (Wikipedia)
The “GNU Project” was started in 1983 with the purpose of driving cooperation within the computing community, such cooperation being restricted by the owners of proprietary software.
The first step was to create an operating system that was compatible with Unix, so that its users could easily switch to GNU. This was no simple task. It involved tremendous amount of work and resources, but was almost completed by 1990. The only part missing was the kernel, which was developed by Linus Torvald in 1991. The operating system commonly known as Linux resulted by combining the Linux kernel and the partially complete GNU system.
In a nutshell
The efforts of a wide community of like-minded people resulted in a free, open-source, versatile and portable operating system, called Linux, widely used by companies and individuals. And it all started because cooperation was seen as a driving force for progress and innovation.