What is the difference between processes and threads in Linux? How does Linux see them internally?

In Linux, processes and threads (threads) are implemented through a unified mechanism — tasks (task_struct). The main difference between a process and a thread is the degree of resource separation:

• Process — a separate address space, own resources (files, memory, etc.).
• Thread — shares the address space and resources with other threads of the same process, differing only by the thread identifier (TID).

In Linux, threads are simply processes that share certain resources. This is achieved through the system call clone(), where you can specify which resources will be shared.

Inside the Linux kernel, each thread is represented by a task_struct structure. A process is a group of such tasks, combined into a process group (thread group), where the first thread is the main process.

Thus, Linux does not make a fundamental distinction between a process and a thread; they are simply tasks with a different set of shared resources.