Linux usage in the modern world
The open source nature of the Linux kernel and its support for multiple hardware architectures made it a very popular choice for custom operating systems, while general-purpose Linux distributions also found wide use in every niche where proprietary Unix systems were used before.
The most popular Linux-based operating system in the world is Android. While most Android applications are written for a custom runtime and never use any functionality of the Linux kernel directly, it’s still a Linux distribution.
Network devices are usually managed through a web GUI or a custom command-line interface, but they still often have Linux under the hood. This applies to consumer-grade Wi-Fi routers, as well as high-performance enterprise and data center routers and switches alike.
General-purpose Linux distributions are also everywhere. Thanks to built-in support for running virtual machines (through Xen or KVM hypervisors), Linux powers the largest cloud computing platforms, including Amazon EC2, Google Cloud Platform, and DigitalOcean. A lot of guest systems are also Linux machines running web servers, database systems, and many other applications.
Linux is also widely used in high-performance computing: all of the most powerful supercomputers in the world are now running Linux on their control and I/O nodes.
Last but not least, the author of this chapter typed these words on a Linux desktop.