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Use ‘top’ to display a dynamic, real-time view of system processes, CPU usage, and memory.
Use ‘sar’ to collect, report, and save system activity information. Part of the sysstat package.
The ‘free’ command displays the total amount of free and used physical and swap memory in the system.
Network connections, routing tables, interface statistics, masquerade connections, and multicast memberships are all displayed by "netstat."
‘ss’ (Socket Statististics) is a utility to investigate sockets. It can display more information than ‘netstat’.