Updated: May 1, 2019
If you want to know how your Linux machine is behaving, you have a range of options: from GUI tools that show nice graphs to simple command-line dashboards to sophisticated statistics collection programs and profilers like dstat and perf. Typically, the GUI tools are the least powerful ones, with best graphics and scantiest information. Except, it does not have to be that way.
KSysGuard is the Plasma system monitor (hint, K letter in the name), designed to shatter the simplicity reputation. Indeed, if you look across the pond, Windows 7 introduced a refined task manager and resource monitor, and then you also get Process Explorer, which offers a deep, multi-dimensional glimpse into the system behavior, pretty colors notwithstanding. KSysGuard is a tool with comparable capabilities, and you just wouldn't believe that from your first encounter with the program. Explore we must.
Tabs, tabs everywhere
Over the past few Plasma releases, KSysGuard has improved steadily, gaining additional granularity, per-process graphlets, extra tools, and then some. But then, you can also expand the existing set of monitors by adding new tabs. By default, you have the Process Table and System Load tabs. Let's add some more.
Once you've created a new tab (sheet), it will be empty. In the right panel, you will have a long list of available sensors - and it is a very long list, pretty much anything your kernel can support and sample under /proc and /sys, more or less. ACPI events, network throughput, disk throughput, various log files, errors, and more. You can drag 'n' drop sensors onto these new sheets, as well as add more than one sensor per graph/display. You can also remove any display you don't like and start fresh. The only limitation is your patience - and your understanding of Linux internals.
You can also download pre-made tabs. Much like the rest of Plasma's wealthy ecosystem, you have add-ons for the system monitor. Wallpapers, themes, icons - and sensors. I grabbed a few and tried them, and indeed, they save you the time of having to configure things yourself. Very practical.
Additional tools & filtering
The Processes and Tools drop-down menus are also rather useful. The former lets you quickly filter information from the process table - like system processes, your own processes, specific programs, etc. If you're not a command line chef, this comes handy. Then, Tools lets you launch additional utilities that can help you get an even better understanding of your system metrics. You can kill application windows, run commands via krunner, check system information, or open a terminal. Very neat.
Then, of course, you can pretty much tweak anything. For each of the plotted graphs or displays, you can change the presentation layer. You can edit the title of the element and stack multiple graphs, use custom ranges, split the view with vertical and horizontal lines, change the color of displayed sensors, and set the polling interval. Almost like working in a spreadsheet program.
Connectivity (remote, too)
And there's still more. A really great feature is the ability to connect to remote hosts. You can use various protocols to get to remote hosts, and even execute (almost) arbitrary commands. This means you have the ability to use a Plasma system as a central monitoring machine for various system metrics without having to configure any third-party tools. This is extremely useful for real work.
KSysGuard is probably the least-effectively named system monitor in the Linux world, but it is without a doubt the most elegant, flexible and extensible one, bringing good looks, extreme customization and a wealth of information to the table. No compromise, you get it all. Plus, you can also monitor remote hosts, w00t.
This program won't necessarily get much spotlight (cough cough), but it definitely deserves it, as it's a great example of what Plasma can do. It is possible to provide a great deal of information without cluttering the interface or having to lose valuable data as a result, and then it allows the user to make the changes they truly need. That's real minimalism.
New tabs and remote connectivity are killer features. You have the ability to get a visual representation of many arcane, obscure and yet critical system metrics, and today, there are almost no UI software that will show you this. The same goes for remote monitoring. You often need complex third-party tools for this. Plasma lets you do this natively, and in a fun way. Even if you're no great fan of Plasma, but you're a techie at heart, I warmly recommend you give this desktop environment a spin. KSysGuard, barring its name, might just be the thing to win your nerdy heart over ... Over and out.