A fully running Linux system consists of many subsystems (introduction, Cpu,memory,io,network, ...). ), monitoring and evaluating these subsystems is part of the performance monitoring. We often need macroscopic view of the whole system state, also need microscopic look at the operation of each subsystem. Fortunately, we don't have to reinvent the wheel to monitor these subsystems with the tools available, and the time-tested, simple and elegant gadgets that grow with Unix are an integral part of our daily unix/linux work.
The following picture summarizes the various subsystems of Linux and the tools needed to monitor them, and if you are interested in Linux system Management (sysadmin & DevOps) and want to get started, you can begin to understand and familiarize yourself with the tools from this diagram. For the skilled Linux cock wire, you should be able to answer this picture with ease. (Image from: Linux performance analysis and Tools, slide is also very exciting, recommend reading against.) )
Linux Performance monitoring: Tools