The Linux operating system is primarily written in the C programming language. The Linux kernel, which is the core component of the operating system, is written in C. This is because C is a low-level language that allows for direct access to the system's memory and resources, making it well-suited for operating system development. Additionally, some parts of the Linux kernel are also written in assembly language, which is a low-level language that is specific to a particular computer architecture. Assembly language is used for performance-critical parts of the kernel, such as the system call interface and the kernel's interrupt handling.
It's worth noting that Linux, as an operating system, is not just the kernel. It comes with user-space utilities, applications, shell and other tools which are written in different programming languages, like C++, Python, Shell, Perl, and many more. These user-space tools are not part of the kernel but provide users with a more rich and interactive experience.
Overall, Linux operating system can be described as a combination of C and assembly languages for kernel and various programming languages for the utilities and tools.