Linux containers are processes with certain isolation features provided by a Linux kernel — including filesystem, process, and network isolation. Containers help with portability — applications can be distributed in container images along with their dependencies, and run on virtually any Linux system with a container runtime.

Although container technologies exist for a very long time, Linux containers were widely popularized by Docker. The word “Docker” can refer to several different things, including the container technology and tooling, the community around that, or the Docker Inc. company. However, in this article, I’ll be using it to refer to the technology and the tooling that manages Linux containers.

What is Docker

Docker is a daemon that runs on your system as root, and manages running containers by leveraging features of the Linux kernel. Apart from running containers, it also makes it easy to manage container images — interacting with container registries, storing images, managing container versions, etc. It basically supports all the operations you need to run individual containers.

But even though Docker is very a handy tool for managing Linux containers, it has two drawbacks: it is a daemon that needs to run on your system, and it needs to run with root privileges which might have certain security implications. Both of those, however, are being addressed by Podman.

Introducing Podman

Podman is a container runtime providing a very similar features as Docker. And as already hinted, it doesn’t require any daemon to run on your system, and it can also run without root privileges. So let’s have a look at some examples of using Podman to run Linux containers.

Running containers with Podman

One of the simplest examples could be running a Fedora container, printing “Hello world!” in the command line:

$ podman run --rm -it fedora:28 echo "Hello world!"

Building an image using the common Dockerfile works the same way as it does with Docker:

$ cat Dockerfile
FROM fedora:28
RUN dnf -y install cowsay

$ podman build . -t hello-world
... output omitted ...

$ podman run --rm -it hello-world cowsay "Hello!"

To build containers, Podman calls another tool called Buildah in the background. You can read a recent post about building container images with Buildah — not just using the typical Dockerfile.

Apart from building and running containers, Podman can also interact with container registries. To log in to a container registry, for example the widely used Docker Hub, run:

$ podman login docker.io

To push the image I just built, I just need to tag so it refers to the specific container registry and my personal namespace, and then simply push it.

$ podman -t hello-world docker.io/asamalik/hello-world
$ podman push docker.io/asamalik/hello-world

By the way, have you noticed how I run everything as a non-root user? Also, there is no big fat daemon running on my system!

Installing Podman

Podman is available by default on Silverblue — a new generation of Linux Workstation for container-based workflows. To install it on any Fedora release, simply run:

$ sudo dnf install podman

Fedora is delightful to use as a graphical operating system. You can point and click your way through just about any task easily. But you’ve probably seen there is a powerful command line under the hood. To try it out in a shell, just open the Terminal application in your Fedora system. This article is one in a series that will show you some common command line utilities.

In this installment you’ll learn how to read files in different ways. If you open a Terminal to do some work on your system, chances are good that you’ll need to read a file or two.

The whole enchilada

The cat command is well known to terminal users. When you cat a file, you’re simply displaying the whole file to the screen. Really what’s happening under the hood is the file is read one line at a time, then each line is written to the screen.

Imagine you have a file with one word per line, called myfile. To make this clear, the file will contain the word equivalent for a number on each line, like this:

one
two
three
four
five

So if you cat that file, you’ll see this output:

$ cat myfile
one
two
three
four
five

Nothing too surprising there, right? But here’s an interesting twist. You can also cat that file backward. For this, use the tac command. (Note that Fedora takes no blame for this debatable humor!)

$ tac myfile
five
four
three
two
one

The cat file also lets you ornament the file in different ways, in case that’s helpful. For instance, you can number lines:

$ cat -n myfile
     1 one
     2 two
     3 three
     4 four
     5 five

There are additional options that will show special characters and other features. To learn more, run the command man cat, and when done just hit q to exit back to the shell.

Picking over your food

Often a file is too long to fit on a screen, and you may want to be able to go through it like a document. In that case, try the less command:

$ less myfile

You can use your arrow keys as well as PgUp/PgDn to move around the file. Again, you can use the q key to quit back to the shell.

There’s actually a more command too, based on an older UNIX command. If it’s important to you to still see the file when you’re done, you might want to use it. The less command brings you back to the shell the way you left it, and clears the display of any sign of the file you looked at.

Just the appetizer (or dessert)

Sometimes the output you want is just the beginning of a file. For instance, the file might be so long that when you cat the whole thing, the first few lines scroll past before you can see them. The head command will help you grab just those lines:

$ head -n 2 myfile
one
two

In the same way, you can use tail to just grab the end of a file:

$ tail -n 3 myfile
three
four
five

Of course these are only a few simple commands in this area. But they’ll get you started when it comes to reading files.

Lots of web developers want to achieve fast loading web pages. As more page views come from mobile devices, making websites look better on smaller screens using responsive design is just one side of the coin. Browser Calories can make the difference in loading times, which satisfies not just the user but search engines that rank on loading speed. This article series covers how to slim down your web pages with tools Fedora offers.

Preparation

Before you sart to slim down your web pages, you need to identify the core issues. For this, you can use Browserdiet. It’s a browser add-on available for Firefox, Opera and Chrome and other browsers. It analyzes the performance values of the actual open web page, so you know where to start slimming down.

Next you’ll need some pages to work on. The example screenshot shows a test of getfedora.org. At first it looks very simple and responsive.

Browser Diet – values of getfedora.org

However, BrowserDiet’s page analysis shows there are 1.8MB in files downloaded. Therefore, there’s some work to do!

Web optimization

There are over 281 KB of JavaScript files, 203 KB more in CSS files, and 1.2 MB in images. Start with the biggest issue — the images. The tool set you need for this is GIMP, ImageMagick, and optipng. You can easily install them using the following command:

sudo dnf install gimp imagemagick optipng

For example, take the following file which is 6.4 KB:

First, use the file command to get some basic information about this image:

$ file cinnamon.png
cinnamon.png: PNG image data, 60 x 60, 8-bit/color RGBA, non-interlaced

The image — which is only in grey and white — is saved in 8-bit/color RGBA mode. That’s not as efficient as it could be.

Start GIMP so you can set a more appropriate color mode. Open cinnamon.png in GIMP. Then go to Image>Mode and set it to greyscale. Export the image as PNG with compression factor 9. All other settings in the export dialog should be the default.

$ file cinnamon.png
cinnamon.png: PNG image data, 60 x 60, 8-bit gray+alpha, non-interlaced

The output shows the file’s now in 8bit gray+alpha mode. The file size has shrunk from 6.4 KB to 2.8 KB. That’s already only 43.75% of the original size. But there’s more you can do!

You can also use the ImageMagick tool identify to provide more information about the image.

$ identify cinnamon2.png
cinnamon.png PNG 60x60 60x60+0+0 8-bit Grayscale Gray 2831B 0.000u 0:00.000

This tells you the file is 2831 bytes. Jump back into GIMP, and export the file. In the export dialog disable the storing of the time stamp and the alpha channel color values to reduce this a little more. Now the file output shows:

$ identify cinnamon.png
cinnamon.png PNG 60x60 60x60+0+0 8-bit Grayscale Gray 2798B 0.000u 0:00.000

Next, use optipng to losslessly optimize your PNG images. There are other tools that do similar things, including advdef (which is part of advancecomp), pngquant and pngcrush.

Run optipng on your file. Note that this will replace your original:

$ optipng -o7 cinnamon.png 
** Processing: cinnamon.png
60x60 pixels, 2x8 bits/pixel, grayscale+alpha
Reducing image to 8 bits/pixel, grayscale
Input IDAT size = 2720 bytes
Input file size = 2812 bytes

Trying:
 zc = 9 zm = 8 zs = 0 f = 0 IDAT size = 1922
 zc = 9 zm = 8 zs = 1 f = 0 IDAT size = 1920
 
Selecting parameters:
 zc = 9 zm = 8 zs = 1 f = 0 IDAT size = 1920

Output IDAT size = 1920 bytes (800 bytes decrease)
Output file size = 2012 bytes (800 bytes = 28.45% decrease)

The option -o7 is the slowest to process, but provides the best end results. You’ve knocked 800 more bytes off the file size, which is now 2012 bytes.

To resize all of the PNGs in a directory, use this command:

$ optipng -o7 -dir=<directory> *.png

The option -dir lets you give a target directory for the output. If this option is not used, optipng would overwrite the original images.

Choosing the right file format

When it comes to pictures for the usage in the internet, you have the choice between:

• JPG or JPEG
• GIF
• PNG
• aPNG
• JPG-LS
• JPG 2000 or JP2
• SVG

JPG-LS and JPG 2000 are not widely used. Only a few digital cameras support these formats, so they can be ignored. aPNG is an animated PNG, and not widely used either.

You could save a few bytes more through changing the compression rate or choosing another file format. The first option you can’t do in GIMP, as it’s already using the highest compression rate. As there are no alpha channels in the picture, you can choose JPG as file format instead. For now use the default value of 90% quality — you could change it down to 85%, but then alias effects become visible. This saves a few bytes more:

$ identify cinnamon.jpg
cinnamon.jpg JPEG 60x60 60x60+0+0 8-bit sRGB 2676B 0.000u 0:00.000

Alone this conversion to the right color space and choosing JPG as file format brought down the file size from 23 KB to 12.3 KB, a reduction of nearly 50%.

PNG vs. JPG: quality and compression rate

So what about the rest of the images? This method would work for all the other pictures, except the Fedora “flavor” logos and the logos for the four foundations. Those are presented on a white background.

One of the main differences between PNG and JPG is that JPG has no alpha channel. Therefore it can’t handle transparency. If you rework these images by using a JPG on a white background, you can reduce the file size from 40.7 KB to 28.3 KB.

Now there are four more images you can rework: the backgrounds. For the grey background, set the mode to greyscale again. With this bigger picture, the savings also is bigger. It shrinks from 216.2 KB to 51.0 KB — it’s now barely 25% of its original size. All in all, you’ve shrunk 481.1 KB down to 191.5 KB — only 39.8% of the starting size.

Quality vs. Quantity

Another difference between PNG and JPG is the quality. PNG is a lossless compressed raster graphics format. But JPG loses size through compression, and thus affects quality. That doesn’t mean you shouldn’t use JPG, though. But you have to find a balance between file size and quality.

Achievement

This is the end of Part 1. After following the techniques described above, here are the results:

You brought image size down to 488.9 KB versus 1.2MB at the start. That’s only about a third of the size, just through optimizing with optipng. This page can probably be made to load faster still. On the scale from snail to hypersonic, it’s not reached racing car speed yet!

Finally you can check the results in Google Insights, for example:

In the Mobile area the page gathered 10 points on scoring, but is still in the Medium sector. It looks totally different for the Desktop, which has gone from 62/100 to 91/100 and went up to Good. As mentioned before, this test isn’t the be all and end all. Consider scores such as these to help you go in the right direction. Keep in mind you’re optimizing for the user experience, and not for a search engine.

Some weeks ago, Steam announced a new addition to Steam Play with Linux support for Windows games using Proton, a fork from WINE. This capability is still in beta, and not all games work. Here are some more details about Steam and Proton.

According to the Steam website, there are new features in the beta release:

• Windows games with no Linux version currently available can now be installed and run directly from the Linux Steam client, complete with native Steamworks and OpenVR support.
• DirectX 11 and 12 implementations are now based on Vulkan, which improves game compatibility and reduces performance impact.
• Fullscreen support has been improved. Fullscreen games seamlessly stretch to the desired display without interfering with the native monitor resolution or requiring the use of a virtual desktop.
• Improved game controller support. Games automatically recognize all controllers supported by Steam. Expect more out-of-the-box controller compatibility than even the original version of the game.
• Performance for multi-threaded games has been greatly improved compared to vanilla WINE.

Installation

If you’re interested in trying Steam with Proton out, just follow these easy steps. (Note that you can ignore the first steps to enable the Steam Beta if you have the latest updated version of Steam installed. In that case you no longer need Steam Beta to use Proton.)

Open up Steam and log in to your account. This example screenshot shows support for only 22 games before enabling Proton.

Now click on Steam option on top of the client. This displays a drop down menu. Then select Settings.

Now the settings window pops up. Select the Account option and next to Beta participation, click on change.

Now change None to Steam Beta Update.

Click on OK and a prompt asks you to restart.

Let Steam download the update. This can take a while depending on your internet speed and computer resources.

After restarting, go back to the Settings window. This time you’ll see a new option. Make sure the check boxes for Enable Steam Play for supported titles, Enable Steam Play for all titles and Use this tool instead of game-specific selections from Steam are enabled. The compatibility tool should be Proton.

The Steam client asks you to restart. Do so, and once you log back into your Steam account, your game library for Linux should be extended.

Installing a Windows game using Steam Play

Now that you have Proton enabled, install a game. Select the title you want and you’ll find the process is similar to installing a normal game on Steam, as shown in these screenshots.

After the game is done downloading and installing, you can play it.

Some games may be affected by the beta nature of Proton. The game in this example, Chantelise, had no audio and a low frame rate. Keep in mind this capability is still in beta and Fedora is not responsible for results. If you’d like to read further, the community has created a Google doc with a list of games that have been tested.

Fedora Classroom sessions continue next week with a session on Fedora Modularity. The general schedule for sessions appears on the wiki. You can also find resources and recordings from previous sessions there. Here are details about this week’s session on Tuesday, October 09 at 1400 UTC. That link allows you to convert the time to your timezone.

Topic: Fedora Modularity 101

As the Fedora Modularity docs page explains, Modularity introduces a new optional repository to Fedora called Modular (often referred to as the “Application Stream” or AppStream for short). This repo ships additional versions of software on independent life cycles. This way users can keep their operating system up-to-date while having the right version of an application for their use case, even when the default version in the distribution changes.

Here’s the agenda for the Classroom session:

Fedora Modularity 101

1. Why Modularity?
2. User demo.
3. Main differences in packager workflows
4.  A walk through the whole process of making a module in Fedora.

Instructor

Adam Samalik is an open source enthusiast using Linux since 2007. He started with many random distributions, then used Arch Linux for a few years, and then switched to Fedora 20 when he realized he needed more stability in his life to get work done.

Adam spends most of his time these days developing and advocating for Fedora Modularity, and also developing the build-side of the new Fedora Docs website.

Other than that, he enjoys giving talks, presenting demos, making graphical designs, and writing — all of that with various levels of proficiency.

Joining the session

This session takes place on Blue Jeans. The following information will help you join the session:

• URL: https://bluejeans.com/6638527489
• Meeting ID (for Desktop App): 6638527489

We hope you attend, learn from, and enjoy this session. Also, If you have any feedback about the sessions, have ideas for a new one or want to host a session, feel free to comment on this post or edit the Classroom wiki page.