Monolithic Kernel

In some UNIX variants and Linux, the monolithic kernel used. In a monolithic kernel, the entire operating system works in kernel space.

Full privilege to access file systems, IPC (inter-process communication), I/O and device managements, fundamental process management, and hardware. These operations are done only by kernel and user applications ask the kernel to do some stuff.

Monolithic kernels are able to dynamically load executable modules at run-time.

Since kernel includes a lot of stuff in monolithic kernels, it gets bigger in size. The kernel is a very big one executable binary and needs to get loaded at boot. Means that, if the kernel gets bigger, it will be harder to boot-up the computer.

Therefore, if you want to modify something, you need to add a new service, you need to modify the entire operating system.