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F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The .apk can be downloaded from their website and has to be installed - of course we have to enable SecurityUnknown sources to get the .apk installed.

However, F-Droid is not a system app[1] and every time we want to install an application from the F-Droid store we would have to enable the Unknown sources checkbox again. We have to install F-Droid as a system app [2] to keep this unchecked.

Download F-Droid:


Use adb to install the package on the phone:

adb push FDroid.apk /mnt/sdcard/
adb shell
mount -o remount,rw /system
cp -i /mnt/sdcard/FDroid.apk /system/app/                 # Use /system/priv-app/ for Android 4.4 and later
chmod 0644 /system/app/FDroid.apk
mount -o remount,ro /system

Reboot the phone, F-Droid should now be a system app.


The OpenVPN Installer failed to install the OpenVPN binary on this Nexus 4 device, so we had to do this manually.

Fetch the package to a local machine:

adb pull /data/app/
unzip assets/openvpn-2.1.1-static-busyboxinxbin
adb push assets/openvpn-2.1.1-static-busyboxinxbin /mnt/sdcard/openvpn

On the device again, as root:

# mount | grep /system
/dev/block/platform/msm_sdcc.1/by-name/system /system ext4 ro,seclabel,relatime,data=ordered 0 0
# mount -o remount,rw /system
# mv /mnt/sdcard/openvpn /system/xbin/openvpn

Remount readonly again:

# mount -o remount,ro /system
# mount | grep /system
/dev/block/platform/msm_sdcc.1/by-name/system /system ext4 ro,seclabel,relatime,data=ordered 0 0

Note: As OpenVPN Installer still would not get the VPN going (and not providing any error messages) I went with OpenVPN Connect after all.

See also:

Rerware Backup

Rerware Backup expects its backups[3] in the following directory structure:


The first part can be configured, the last part seems to be hardcoded.

SD Rescan

With Android 4.4, rescanning the SD card for new/changed files[4] does not work anymore[5], because the "MEDIA_MOUNTED" broadcast intent has been restricted to system applications[6]

This means that apps like Rescan Media won't work on Android 4.4. Use SD Scanner instead.


The native SIP client[7] is a very basic SIP client and tends to have echo issues[8][9] too.

For that reason we're using csipsimple to make internet calls:

  • In Settings, select Media and enable Echo cancellation (if not already enabled)
  • To set a trunk prefix (e.g. "use 0 to dial out") select Modify Account and choose Filters. In here, add two rules:
    • Starts with 0 → Prefix by 0
    • Starts with + → Replace match by 000. Adjust the last 2 zeros with the calling code of your country.