The Linux kernel is the core interface between a computer’s hardware and its processes, and it is the most important component of a Linux operating system (OS). It communicates between the two, allowing for the most efficient use of resources.
The kernel is so named because it exists within the OS and controls all of the major functions of the hardware, whether it’s a phone, laptop, server, or any other type of computer, much like a seed inside a hard shell.
What the Kernel Does?
The kernel has 4 main jobs as described below.
Memory Management
Keep track of how much memory is being used to store what and where it is being stored.
Process Management
Determine which processes, when, and for how long the central processing unit (CPU) can be used.
Device Drivers
Act as a liaison between the hardware and the processes.
System Calls and Security
Receive service requests from the processes.
If implemented correctly, the kernel is completely invisible to the user, operating in its own little world known as kernel space, where it allocates memory and keeps track of where everything is stored. The user space refers to what the user sees, such as web browsers and files. A system call interface is used by these applications to communicate with the kernel (SCI).
Consider the following scenario: The kernel works as a personal assistant to a high-ranking executive (the hardware). It is the assistant’s responsibility to relay messages and requests (processes) to the executive from employees and the general public (users), to remember what is stored where (memory), and to determine who has access to the executive at any given time and for how long.
Kernel Context within the Operating System
To put the kernel into perspective, consider a Linux machine as having three layers.
Hardware
The physical machine is the system’s foundation, consisting of memory (RAM) and the processor (CPU), as well as input/output (I/O) devices such as storage, networking, and graphics. The CPU performs calculations and reads and writes data to and from memory.
The Linux Kernel
The core of the OS. It’s software residing in memory that tells the CPU what to do.
User Processes
These are the programs that are currently running and are managed by the kernel. User processes are what make up user space collectively. User processes are also referred to as simple processes. Additionally, the kernel enables communication between these processes and servers (known as inter-process communication, or IPC).
The system’s code runs on CPUs in one of two modes: kernel mode or user mode. Kernel mode code has unrestricted access to the hardware, whereas user mode code has limited access to the CPU and memory to the SCI. Memory is separated in a similar way (kernel space and user space). These two minor details serve as the foundation for more complex operations such as privilege separation for security, container and virtual machine construction.
This also means that if a process fails in user mode, the damage is limited and the kernel can recover it. A kernel process crash, on the other hand, can crash the entire system due to its access to memory and the processor. Because there are safeguards in place and permissions are required to cross boundaries, user process crashes should not cause too many issues.
