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My favorite Linux top command options Don Watkins Mon, 03/21/2022 - 03:00 Up Register or Login to like.

When I am checking out Linux systems (or even troubleshooting computers running other operating systems), I frequently use the top command to check out the system's RAM and CPU utilization. It provides me with information to assess the computer's overall health. I learned about the top command early in my Linux journey and have relied on it to give me a quick overview of what is happening on servers or other Linux systems, including Raspberry Pi. According to its man page, the top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of processes or threads currently being managed by the Linux kernel.

A quick overview is often all I need to determine what is going on with the system in question. But there is so much more to the top command than meets the eye. Specific features of your top command may vary depending on whose version (procps-ng, Busybox, BSD) you run, so consult the man page for details.

To launch top, type it into your terminal:

$ top

Running processes are displayed below the table heading on the top screen, and system statistics are shown above it.

Top 05:31:09 up 55 min,3 users,load average: 0.54, 0.38, 0.46
Tasks: 469 total, 1 running, 468 sleeping,  0 stopped, 0 zombie
%Cpu(s): 1.0 us, 0.4 sy, 0.0 ni, 98.6 id, 0.1 wa, 0.0 hi,0.0 si,0.0 st
MiB Mem : 32116.1 total,  20256.5 free, 6376.3 used, 5483.3 buff/cache
MiB Swap: 0.0 total,  0.0 free,      0.0 used.  25111.4 avail Mem  

 PID USER  PR NI   VIRT    RES   SHR S %CPU %MEM    TIME+ COMMAND                                                
2566 don   20  0  11.9g 701300 78848 S  3.3  2.1  2:03.80 firefox-bin
1606 don   20  0  24.2g  88084  4512 S  2.0  0.3  0:39.59 elisa
1989 don   20  0 894236 201580 23536 S  2.0  0.6  0:46.12 stopgo-java
5483 don   20  0  24.5g 239200 20868 S  1.3  0.7  0:26.54 Isolated Web Co
5726 don   20  0 977252 228012 44472 S  1.3  0.7  0:41.25 pulseaudio

Press the Z key to change the color of the output. I find this makes the output a little easier on the eyes.

Press the 1 key to see a graphical representation of each CPU core on the system. Press 1 repeatedly to assess core statistics for your CPU cores.

You can display memory usage graphically by invoking the top command and then pressing the m key.

More Linux resources Linux commands cheat sheet Advanced Linux commands cheat sheet Free online course: RHEL technical overview Linux networking cheat sheet SELinux cheat sheet Linux common commands cheat sheet What are Linux containers? Our latest Linux articles Useful top options

If you're looking only for the processes started by a specific user, you can get that information with the -u option:

$ top -u 'username'

To get a list of idle processes on your system, use the -i option:

$ top -i

You can set the update interval to an arbitrary value in seconds. The default value is three seconds. Change it to five like this:

$ top -d 5

You can also run top on a timer. For instance, the following command sets the number of iterations to two and then exits:

$ top -n 2Locate a process with top

Press Shift+L to locate a process by name. This creates a prompt just above the bold table header line. Type in the name of the process you're looking for and then press Enter or Return to see the instances of that process highlighted in the newly sorted process list.

Stopping a process with top

You can stop or "kill" a running process with top, too. First, find the process you want to stop using either Shift+L or pgrep. Next, press K and enter the process ID you want to stop. The default value is whatever is at the top of the list, so be sure to enter the PID you want to stop before pressing Enter, or you may stop a process you didn't intend to.

Top top

There are many iterations of the top command, including htop, atop, btop, and ttop. There are specialized top commands, too, like powertop for power usage and ntop for networks. What's your favorite top?

A quick overview is often all I need to determine what is going on with my Linux system. But there is so much more to the top command than meets the eye.

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Opensource.com

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Upstream first or the path lifting property of a covering space Aleksandra Fedorova Mon, 03/21/2022 - 03:00 Up Register or Login to like.

Don't be scared; when you reach the end of this article, you will understand its title.

Understand spaces

Geometry and Topology is an area of mathematics that deals with spaces, usually topological, and various additional structures you can define on them.

How do you turn a set of elements into a list? "You use the list() function!" say my Pythonic friends. But essentially, you add the idea of an order. You take the set and explain which point in that set is next. Similarly, spaces are sets of elements with these additional concepts:

• For a topological space, add the idea of a neighborhood. You explain how to tell that two points are close.
• For a metric space, add the idea of a distance. You explain how to measure the distance between any two points of the set.

There are many types of spaces in mathematics, from a well-known Euclidean space to a less known but not less common differentiable manifold all the way to exotic structures invented moments ago. And the research in this area circles around finding relationships between different structures and determining whether they define the same basic object.

For example, it is quite easy to prove that a metric space is always a topological space. But it is a bit harder to show that there are topological spaces that can not be expressed in terms of distance.

However, for the casual weekend topologists out there, I recommend two-dimensional surfaces, for example, the good old sphere, torus, or a Mobius strip. Not as square and flat as the Euclidean plane, but still manageable. And the classification theory of two-dimensional compact manifolds is a lot of fun.

Covering space

Take a spring coil and look at it from the top. You will see a circle.

 

Expressing this fact in mathematical language, you would say that the coil itself is the total space. In this case, on its own, it is just a one-dimensional line. It is made up of various components:

• The circle you see is a base space.
• The line of sight defines the covering map.
• If you had a laser sight, the points where the laser would cut the coil would be called a fiber.

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And altogether, total space, base space, and covering map define the covering space or a covering of a circle by a line with discrete fiber.

Homework: Can a circle cover a line?

The critical quality of the covering space, which makes it different from just any projection, is that the neighborhood of each fiber point in the total space works very much the same as the neighborhood of its projection in the base space. This allows you to reason about specific properties of a total space using the pre-existing knowledge of a base space and vice versa.

And mathematicians just love to move between spaces in this way. Once you hit a certain roadblock with the space you are currently researching, you craft a clever mapping of the space onto familiar grounds. You prove something there and then transfer the result back into the original space, where it can lead to new and exciting breakthroughs.

Path lifting property

What does it all have to do with upstream first?, you may ask. (We are yet in the early stages of developing a proper mathematical apparatus for this theory. Feel free to add your suggestions and corrections in the comments section below.)

Look at how code is delivered to an enterprise-level Linux distribution, for example, CentOS Stream. There is an open source project and community which develops a specific version of a piece of software, for example, Firefox. We call such a project upstream. Once the upstream project releases a Firefox version, it gets packaged to Fedora. And then someday, the new CentOS Stream version is bootstrapped using the content of the Fedora package, which contains a specific version of Firefox from the upstream project.

When the upstream project releases a critical update of Firefox, the update is packaged and released in Fedora. But it is also packaged and released via CentOS Stream.

The FOSS space

Consider the set of all patches to all upstream projects, Fedora, and CentOS Stream. Obviously*, this is a topological space, where the Git history defines the neighborhood of a patch.

(*) Sometimes mathematicians use the word obviously to hide the fact that they can not really explain the concept in detail.

This space is not easy to grasp, and while you can connect some of the dots with a path, its global properties are yet to be explored.

The covering map

Take any commit in the FOSS space and map it to a commit in CentOS Stream, which implements the same functionality or fixes the same issue. For a regular commit in CentOS Stream, the map is trivial. The map points to its downstream version for any upstream change or a change in Fedora. Therefore, FOSS space can be represented as a covering space with CentOS Stream as its base.

Lifting a path

The path lifting property tells you that for every path in the base (a change in CentOS Stream), there should be a lifted path in the layers (a change in Fedora and in the upstream project, which maps onto it). In other words, it represents the same bugfix.

And the upstream first principle tells you to build that path.

Wrap up

Applying mathematical concepts to FOSS deployments provides new and interesting ways of understanding the interrelated nature of open source software. I hope this has been an insightful and interesting foray into space and the upstream first principle.

Applying mathematical concepts to FOSS deployments provides new and interesting ways of understanding the interrelated nature of open source software.

Image by:

João Trindade. Modified by Jason Baker. CC BY-SA 2.0.

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