System monitoring in Linux and Unix environments encompasses real-time observation and historical analysis of system resources — CPU, memory, disk, network, and processes. From basic utilities like top and ps that ship with every distribution, to modern interactive tools like htop and btop, monitoring helps identify bottlenecks, diagnose failures, and optimize performance. Understanding load average (runnable + uninterruptible processes over 1, 5, and 15 minutes) differs from instantaneous CPU usage — the former reveals sustained pressure, the latter shows a snapshot. A key insight: iowait is not CPU time lost to waiting — it's idle time during which at least one I/O operation was pending, meaning high iowait with low CPU usage often indicates disk or network bottlenecks, not CPU saturation.