Category Archives: Linux

F-Droid and installing .apk files

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This post is about getting F-Droid or any. apk file on your phone. I’ve used the steps below to get my IceCo mobile android application on my own and families phones.

Developer mode (and USB debugging)

Faiphone 4

My Fairphone 4 has Android 13 on it (Api level 33). To turn developer modus on, perform:

  • Goto ‘Settings’ / ‘Instellingen’.
  • Scroll down to ‘About phone’ / ‘About device’ / ‘Over de telefoon’.
  • Scroll down to ‘Build numer’ / ‘Buildnummer’.
  • Tap this 7 times.
  • To turn it off again: goto ‘Settings’ / ‘Instellingen’.
  • Scroll down to ‘System’ / ‘Systeem’.
  • Scroll to ‘Developer option’ / ‘Ontwikkelaaropties’.
  • Sidenote: turn USB debugging on here if you want to build from your laptop.
  • Turn them off in this screen.

Old Samsung phone

My old Samsung A520 phone has Android 8 on it (Api level 26). To get into developer modus try:

  • Goto ‘Settings’ / ‘Instellingen’.
  • Scroll down to ‘About phone’ / ‘Info telefoon’.
  • Goto ‘Software information’ / ‘Softwaregegevens’.
  • Tap ‘Build number’ / ‘Buildnummer’ 7 times.
  • To turn it off again: goto Settings’ / ‘Instellingen’.
  • Scroll down to ‘Developer options’ / ‘Ontwikkelaarsopties’.
  • Use to switch to turn if ‘On’ or ‘Off’ / ‘Aan’ or ‘Uit’.
  • In this same menu, toggle the USB debugging option.

Samsung Galaxy Watch(4)

To get a Gear Watch(4) into developer modus, perform:

  • Go to ‘Settings’ / ‘Instellingen’
  • Scroll down to ‘About Watch’ / ‘Over het horloge’
  • Scroll to ‘Software Information’ / ‘Software informatie’
  • Then tap 5 times on the ‘Software version’
  • In the ‘Settings’ menu, you’ll have a lot more options now
  • To turn it off again, tap it 5 times again

Copy paste .apk files (dangerous)

To get an Android .apk, like F-Droid or your own build .apk file on your phone, you’ll have to allow installation of external sources.

Make sure, once you have your .apk file installed, to disable to installation from unknown sources again.

Android 13

  • Goto ‘Settings’ / ‘Instellingen’.
  • Goto ‘Apps’.
  • Below the apps displayed, scroll down to ‘Special app access’ / ‘Speciale app-toegang’.
  • Find and select ‘Install unknown apps’ / ‘Onbekende apps installeren’.
  • My list of apps was very short and missed a file explorer or something like that.
  • I selected ‘Adblock browser’ because that app was present in this list, then installed the .apk file (like F-Droid). Then deselected the ‘Adblock browser’ for safety reasons.

Android 8 or Android 11

  • Goto ‘Settings’ / ‘Instellingen’
  • Goto ‘App & notifications’ / ‘Apps’
  • Select the three dots in the upper right corner, select ‘Special app access’ / ‘Speciale toegang’, or ‘Security/Privacy’ then ‘Installation sources’.
  • Scroll down to ‘Unknown apps’ / ‘Onbekende apps installeren’.
  • On my Android 8 phone, the ‘File explorer’ / ‘Mijn bestanden’ was available here : )
  • Select the app you think will do.

Once the app you want to install is present, make sure you disable the ‘Install from unknown source’ option again! And now F-Droid is installed, you can select F-Droid as a safe option to installe from.

Ubuntu for mobile (Android) Java development

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Linux

This blog is about setting up a proper Linux Ubuntu environment to use when developing mobile applications for Android. Goal is to use 100% Java using JavaFX and IntelliJ.

I took an old laptop and luckily it had a SSD drive which still functioned. Here are some steps I took to get this laptop up and running for mobile Java development running Ubuntu.

First step is to goto https://ubuntu.com/download/desktop and download the iso image. Then proceed to https://rufus.ie/en/ to get the (portable) version of Rufus. Format a USB stick, put the iso image on the stick using Rufus. Actually, https://phoenixnap.com/kb/install-ubuntu-24-04 is a great guideline to install Linux. Most difficult part for me was to get my laptop to boot from USB (as you can imagine that should be quite easy, you understand installing Linux is easy).

Java

Install some java distributions:

apt install openjdk-17-jre-headless
apt install openjdk-21-jre-headless
apt install openjdk-17
apt install openjdk-21

Of course, download IntelliJ from https://www.jetbrains.com/idea/download/?section=linux and install it for example in /pub/software (and create a symbolic link called ‘idea’ to it).

Not really necessary, but sometimes useful, I installed SQL Developer (choose other platforms and just download the zip version). I’ve unpacked it in /pub/software/sqldeveloper. To get it to work using Java 17:

vi /pub/software/sqldeveloper/sqldeveloper/bin/sqldeveloper.conf

And put this on the second or third line

SetJavaHome /usr/lib/jvm/java-17-openjdk-amd64

The mentioned Java versions are for many reasons useful to have present on your system, but to develop mobile applications on your system, I use GraalVM with Gluon to build native images you can deploy and run on your phone. It is my experience that it’s a very delicate process to get all your add-ons versions aligned properly.

GraalVM (with Gluon)

So, next step is to goto https://github.com/gluonhq/graal/releases and download some latest stable and latest dev versions.

Besides the GraalVM with Gluon builds, it’s also useful to have a GraalVM JDK present (without Gluon), use https://github.com/graalvm/graalvm-ce-builds/releases for this. I’ve downloaded and extracted them in /pub/software.

Besides the JDK, it’s also required to download Android NDK (for C or C++ usage) and the Android SDK (because I don’t want to use Android Studio). I’ve downloaded them to /pub/android from https://developer.android.com/ndk/downloads and https://developer.android.com/studio/index.html#command-line-tools-only

Maven

When you’ve installed your favorite IntelliJ version, it comes with a Maven version (mine has 3.9.9 shipped), maybe download the 3.8.8 version as well from https://dlcdn.apache.org/maven/maven-3/3.8.8/binaries/ and put it in /pub/software. It might look like the following now.

Some packages needed for JavaFX in the future:

apt-get install libfreetype6-dev
apt-get install libgtk-3-dev

From https://github.com/gluonhq/substrate, I read that also the following has to be installed:

apt-get install libasound2-dev libavcodec-dev libavformat-dev libavutil-dev libfreetype6-dev
apt-get install libgl-dev libglib2.0-dev libgtk-3-dev libpango1.0-dev libx11-dev libxtst-dev zlib1g-dev

I use the following startup script to launch IntellilJ


#!/bin/bash
export M2_HOME="/pub/software/idea/plugins/maven/lib/maven3"
export GRAALVM_HOME="/pub/software/graalvm-gluon-23"
export JAVA_HOME="/pub/software/graalvm-gluon-23"
export ANDROID_NDK="/pub/android/ndk"
export ANDROID_SDK="/pub/android/sdk"
export ANDROID_HOME="/pub/android/sdk"
export ANDROID_SDK_ROOT="/pub/android/sdk"
export ANDROID_NDK_ROOT="/pub/android/ndk"

# export AR="aarch64-linux-android-ar"
# export CC="aarch64-linux-android30-clang"
# export CXX="aarch64-linux-android30-clang++"

export PATH="$ANDROID_NDK/toolchains/llvm/prebuilt/linux-x86_64/bin:$ANDROID_HOME/platform-tools:$ANDROID_HOME/cmdline-tools/latest/bin:$GRAALVM_HOME/bin:$M2_HOME/bin:$ANDROID_NDK:$ANDROID_SDK:$PATH"

cd ~/.m2
rm settings.xml
ln -sf $M2_HOME/conf/settings.xml settings.xml

cd /pub/software/idea/bin
./idea

The AA CC and CXX exports are necessary when you want to compile to native libraries. You’ll also notice the link from ~/.m2 to the Maven settings. This because IntelliJ sometimes resets the Maven settings back to ~/.m2

settings.xml (maven)

As you might have linked to the $M2_HOME/conf/settings.xml file. Or not, keeping a ~/.m2/settings.xml file is just as good. In all cases, the settings.xml should look something like this:

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>/pub/repository</localRepository>
  <profiles>
    <profile>
      <id>artifactory</id>
      <repositories>
        <repository>
          <id>gluon-releases</id>
          <url>https://nexus.gluonhq.com/nexus/content/repositories/releases/</url>
        </repository>
        <repository>
          <id>maven-central</id>
          <url>https://repo.maven.apache.org/maven2/</url>
        </repository>
      </repositories>
      
      <pluginRepositories>
        <pluginRepository>
          <id>gluon-releases</id>
          <url>https://nexus.gluonhq.com/nexus/content/repositories/releases/</url>
        </pluginRepository>
        <pluginRepository>
          <id>maven-central</id>
          <url>https://repo.maven.apache.org/maven2/</url>
        </pluginRepository>
      </pluginRepositories>
    </profile>
  </profiles>
  <activeProfiles>
    <activeProfile>artifactory</activeProfile>
  </activeProfiles>
</settings>

IntelliJ

If you start IntelliJ using the script mentioned earlier, open a terminal and type the following:

native-image --version
mvn -version
java -version

When upgrading any part of your setup, make sure to keep the old versions and create a new startup script. Using this method, you can be sure to build the newer version of your mobile app alongside a current version which works.

First step is actually get it to work on your mobile phone, that’s the difficult one. After that, nothing is holding you back.

IntelliJ toolbar back and forward to file button

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I’m a fan of using the Ctrl-Alt-Left and Ctrl-Alt-Right keyboard shortcuts, but in some environments (remote desktop connection within a Citrix connection) they just do not work and without enough privileges to change the desktop shortcuts for Linux, the following is nifty.

If not so already, make the toolbar visible: View -> Appearance -> Toolbar

Next, rightclick the Toolbar and select Customize Toolbar. In the Main Toolbar section, below General Actions press Add (Action) or on the dashed line, select add action below from the rightclick-mouse-menu.

Open the Main Menu, open the Navigate Menu. The first 2 options are Back and Forward : ) Hopefully, you have now this:

Automatically reload / renew java cacerts in keystore

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In our current project we have a Nexus server as artifactory repository manager. Setup is not entirely finished and one drawback is that the certificate is only valid for 3 days.

The following script downloads the certificate and uses keytool to import the certificate only when it’s a new one (using the same alias)

#!/bin/bash
true | openssl s_client -connect nexus.mycompany.com:443 2>/dev/null | openssl x509 > ~/Downloads/nexus-crt.crt
DIFF=$(diff ~/Downloads/nexus-crt.crt ~/Downloads/nexus.mycompany.com.crt)
if [ "$DIFF" ]
then
   echo "Reloading Nexus certificate"
   cp ~/Downloads/nexus-crt.crt ~/Downloads/nexus.mycompany.com.crt
   cd ~/.sdkman/candidates/java/current/bin
   ./keytool -delete -alias nexus-crt -cacerts -storepass changeit
   ./keytool -importcert -noprompt -trustcacerts -cacerts -alias "nexus-crt" -file ~/Downloads/nexus.mycompany.com.crt -storepass changeit
   cd -
fi

If you want to display the certificates enddate:

echo "cert enddate: cat ~/Downloads/nexus-crt.crt | openssl x509 -noout -dates | tail -1 | sed 's/[^ ]*=//' "

gitlab git mvn pull all clean all

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Suppose you have a directory /pub/gitlab with all your git projects, but also a logs directory which can be skipped.

user@server:~$ cat > cleanall
cd /pub/gitlab
for d in */ ; do
log=$(basename $d)
[[ $log =~ ^(logs)$ ]] && continue
cd "$d"
echo -n "$d : "
mvn clean
cd ..
done

user@server:~$ cat > pullall
cd /pub/gitlab
for d in */ ; do
log=$(basename $d)
[[ $log =~ ^(logs)$ ]] && continue
cd "$d"
echo -n "$d : "
git pull
cd ..
done