strongSwan on Android

strongSwan VPN Client for Android

We maintain the strongSwan VPN Client for Android, an App that can be downloaded directly from Google Play. More details can be found on a separate page.

Native Build

Using a standalone toolchain from the Android NDK strongSwan can be built to run as a console application/daemon on rooted Android systems.

Standalone Toolchain

Detailed instructions on how to create a standalone toolchain can be found in the Android NDK docs. Something like the following will do:

$NDK/build/tools/ --arch=<arm|x86|mips> \
    --platform=android-<API level> --install-dir=<path/to/toolchain>

For the instructions in the next section let’s assume the toolchain was created like this:

$NDK/build/tools/ --arch=arm \
    --platform=android-21 --install-dir=/tmp/strongswan-toolchain

Build strongSwan

Using the standalone toolchain created before strongSwan can be built from a source tree (or the repository) pretty much as usual. Therefore, refer to the installation documentation for a general instruction on how to build strongSwan from sources.

To cross-compile strongSwan for Android use the following when running ./configure (--host has to be adapted according to the selected architecture/toolchain):

export PATH=/tmp/strongswan-toolchain/bin:$PATH
./configure --host=arm-linux-androideabi <other options as needed>
Depending on the API level, the older Linux headers included in the toolchain might make it necessary to add some additional headers in src/include or to revert the headers there to versions closer to the ones included in the toolchain.

System Image

strongSwan can also be built for inclusion in an Android system image, i.e. directly within the Android source tree. The rest of this document describes how to do so.

These instructions are quite old and might not work anymore.

Android Source Tree

You will need the complete Android source tree to build strongSwan. Instructions on how to download and build it can be found on the Android website. To checkout a specific branch or tag of the sources, specify it with the -b parameter when using the repo init command.

Since building the whole source tree takes quite a while you should probably start with this first (use -j to speed this up on multi-core machines):

cd /path/to/android/source
. build/
lunch <target>
make -j<jobs>

Android Kernel

The prebuilt kernel that is used for the emulator lacks some modules required for strongSwan to work correctly. It is therefore required to build a custom kernel. To get the current kernel config you can use the Android Debug Bridge to download it from the running emulator. After starting the emulator use

adb pull /proc/config.gz config.gz

to copy the config to the current directory. Then enable the missing modules, this is mainly CONFIG_XFRM_USER and CONFIG_INET_XFRM_MODE_TUNNEL but might include other modules. Please compare your config to the list of required modules. Please note that some modules, especially all the IPv6 related modules, are not really required.

Clone the kernel sources and check out an appropriate tag (check the version of the kernel in the emulator). For example (this is for Android 2.2):

git clone kernel
cd kernel
git checkout -t origin/android-goldfish-2.6.29

You can then copy your config to this directory and compile the kernel sources using

export ARCH=arm
export CROSS_COMPILE=/path/to/android/source/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi-
make oldconfig
make -j<jobs>

To start the emulator using your custom kernel use the following command.

emulator -kernel /path/to/kernel/source/arch/arm/boot/zImage &


Optionally libcurl can be used to fetch CRLs. The library is also required if you intend to build scepclient. You can build the libcurl library with droid-gcc.


Since droid-gcc is written in Ruby you’ll obviously need Ruby installed on your build system. Then download droid-gcc by either cloning the Git tree (clone git:// or by downloading it directly.

If you used Git you can install droid-gcc using make install. If you downloaded it directly, you have to manually create two symlinks to droid-gcc named droid-gcc and droid-ld in a directory that is included in your PATH environment variable.

Build the Library

To simplify building the libcurl library, a build script and an Android Makefile are attached to this page. Download the two helper files to an appropriate working directory and then download and extract the current source tarball of libcurl.

Adjust the variables in the build script (DROID_ROOT and optionally DROID_TARGET and INSTALLDIR). Make sure you specify DROID_ROOT@ as an absolute path. Then build and install *libcurl using

cd curl-x.x.x
. ../


Now you are ready to build strongSwan. Download the current tarball and extract it in DROID_ROOT/external. A symlink to the strongSwan source tree also works with newer Android releases.

If you build directly from the strongSwan Git repository instead of a tarball, the sources have to be prepared properly, otherwise the build will fail. In the root of the strongSwan sources run the following to create the required files (this has some external dependencies, see HACKING for details):

./ && ./configure && make dist && rm strongswan-*.tar.gz

If you changed INSTALLDIR in the build scripts above, you will have to change the top (or accordingly. You can also adjust the plugin list in the that file or enable/disable executables.

The executable you want to include in the system image (charon, scepclient) have to be added to PRODUCT_PACKAGES in build/target/product/ The libraries are automatically installed.

Now just build the Android source tree.

cd /path/to/android/source