Konstantin Tutsch

Grant Docker Access To Volume on SELinux Enforced System

Mon, 17 Nov 2025 15:06:00 +0100

When running Docker on a system enforcing SELinux, Docker Volumes require a special SELinux context to be accessible by the Docker Daemon and Container.

This context is called container_file_t and can be set on a path recursively:

semanage fcontext -a -t container_file_t "<path>(/.*)?"

Afterwards, the context needs to be applied to already existing files:

restorecon -Rv <path>

Your <path> is now usable by Docker as a volume! 🥳

How To Compile a Java Program with Multiple Source Files

Thu, 05 Sep 2024 18:12:52 +0200

This blog post is just another note to my future self. This time, it is about compiling (and running) a Java application (with multiple source files) from only the command line.

The Example Program

Let's say, our application is made up of two files: Main.java and Combination.java. In this example, their contents look like this …

// Main.java

package com.konstantintutsch.Example;

public class Main
{
    private static Combination c;

    public static void main(String[] args)
    {
        c = new Combination("Hello, World!", 42);

        System.out.println(c.getText() + " (" + c.getNumber() + ")");
    }
}

… and like this:

// Combination.java

package com.konstantintutsch.Example;

public class Combination
{
    // Attributes
    private String text;
    private int number;

    // Methods
    public Combination(String text, int number) // Constructor
    {
        this.text = text;
        this.number = number;
    }

    // text
    public String getText()
    {
        return this.text;
    }
    public void setText(String text)
    {
        this.text = text;
    }

    // number
    public int getNumber()
    {
        return this.number;
    }
    public void setNumber(int number)
    {
        this.number = number;
    }
}

In this case, our entry point into the code of our program is the class Main from Main.java.

Compiling

If we want to compile and later execute this code, we need to create a JAR file.

Here's the procedure:

Compile all .java source files to .class files
Bundle these .class files into a .jar file

Commands

The procedure, but translated into commands, looks like this:

mkdir ./build
javac -d ./build Main.java Combination.java
jar cfe ./build/Build.jar com.konstantintutsch.Example.Main -C ./build com

Explanation

javac
- -d ./build: write all .class files to ./build/<PACKAGE>
- *.java: file(s) to be compiled
jar
- c: create a JAR
- f: write the archive to a file (./build/Build.jar)
- e: use a class as the entry point (com.konstantintutsch.Example.Main)
- -C ./build com: bundle all .class files in the directory ./build from the namespace com (also com.konstantintutsch.Example) into the archive

Makefile

If you don't want to retype these same commands every time you change something in your code, write a Makefile:

#
# Package
#

NAMESPACE := com
PACKAGE := $(NAMESPACE).konstantintutsch.Template

#
# Files
#

SOURCES := $(wildcard *.java)

BUILDDIR := build
EXECUTABLE := Build.jar

#
# Compilers
#

JC := javac
JCFLAGS := -d $(BUILDDIR)

JR := jar

#
# Build
#

$(BUILDDIR):
	mkdir -p $(BUILDDIR)

$(BUILDDIR)/$(EXECUTABLE): $(BUILDDIR)
	$(JC) $(JCFLAGS) $(SOURCES)
	$(JR) cfe $(BUILDDIR)/$(EXECUTABLE) $(PACKAGE).Main -C $(BUILDDIR) $(NAMESPACE)

Compiling now looks like this:

make build/Build.jar

Much shorter!

Executing

The last thing to do now is to run the code:

$ java -jar ./build/Build.jar
Hello, World! (42)

Look at that! It worked!

At least on my end …

How-To Use BeaconDB as Your Geolocation Provider on Linux

Tue, 13 Aug 2024 18:35:40 +0200

MLS and It's Alternative

On March 13, 2024, Mozilla decided to retire their geolocation service and database.¹

This is probably the reason you are currently reading this post and I can also safely assume that your system is not able to locate itself anymore. No worries though, there's a quick fix.

It's BeaconDB! An open-source alternative to the Mozilla Location Service. It's still in an experimental stage, but already pretty mature. And to our luck, also uses the same request format as Mozilla.²

The Fix, at least with GNOME via Geoclue

On most Linux distributions, location services are provided by a service called Geoclue. Though by default, current and older versions of Geoclue are configured to use MLS as their geolocation database.

That's a problem when MLS doesn't work. And that is the case forever now. Fortunately, switching over to BeaconDB is easy.

First, find geoclue.conf. It's location differs on different distributions with different package manages. On Fedora, you can find it at /etc/geoclue/geoclue.conf.

Once found, edit the file as root.

[wifi]
enabled=true
url=https://beacondb.net/v1/geolocate

To apply the configuration change, restart the Geoclue service. On systems using SystemD, do this (and be root):

systemctl restart geoclue.service

That's it. Open an app that's using location services and try out your system's regained capabilities!

Troubleshooting

If your system indefinitely tries to locate itself without any success or even fails, your area might not be indexed.³

Have a look at the BeaconDB website to find out which contribution options might be viable to you. Have fun!

Multiple Push URLs for a Single Git Remote

Fri, 12 Jul 2024 10:23:00 +0200

This post is just a note to my future self on how to add multiple push URLs to a single git remote.

Adding The URLs

First, add a new remote to your git repository.

git remote add all git@server1:repo.git

Then, redefine the push URL of the remote.

git remote set-url --add --push all git@server1:repo.git

Finally, add the URL of your second remote.

git remote set-url --add --push all git@server2:repo.git

Confirming The Changes

At the end, confirm that all URLs were set correctly.

git remote -v

The output should now be similar to this:

all	git@server1:repo.git (fetch)
all	git@server1:repo.git (push)
all	git@server2:repo.git (push)