All major operating systems come with a more or less standard set of tools that can extract and sometimes visualize important pieces of performance-related information from the network, hardware, and the OS itself. Here, we will mention a few of the most useful grouped by the OS that they come bundled with.
In UNIX and Linux-based operating systems, there are a lot of useful tools available as shell-executable commands. These tools will assist in monitoring system activities. The most common one might be the top command, which will give an interactive and real-time feed of processor activity and memory usage. Its output can be adapted to most needs, so it is, as it always is with UNIX-based commands, a good idea to read through its main pages. A basic output from top in Linux can look similar to the following example (the output has been limited to a few lines, as it normally is very long):
> top Tasks: 230 total, 1 running, 229 sleeping, 0 stopped, 0 zombie %Cpu...