Build a Statically Linked or Mostly-Statically Linked Native Executable

GraalVM Native Image by default builds dynamically linked binaries: at build time it first loads your application classes and interfaces, and then hooks them together in a process of dynamic linking.

However, you can create a statically linked or mostly-statically linked native executable, depending on your needs.

A static native executable is a statically linked binary that you can use without any additional library dependencies. A static native executable is easy to distribute and deploy on a slim or distroless container (a scratch container). You can create a static native executable by statically linking it against musl-libc, a lightweight, fast and simple libc implementation.

A mostly-static native executable is a binary that links all the shared libraries on which the native executable relies (zlib, JDK-shared static libraries) except the standard C library, libc. This is an alternative option to statically linking everything. Also, depending on the user’s code, it may link libstdc+ and libgcc. This approach is useful for deployment on a distroless container image.

This guide shows how you can take advantage of Native Image linking options including fully dynamic, fully static, and mostly-static (except libc) to generate an executable ideal for your deployment scenario.

Prerequisites and Preparation

The easiest way to install GraalVM is with SDKMAN!. For other installation options, visit the Downloads section.

To create statically linked applications with Native Image, you require a musl toolchain with the zlib library. For the best compatibility, use musl-1.2.4 or later. We recommend building musl from source as shown below:

# Specify an installation directory for musl:
export MUSL_HOME=$PWD/musl-toolchain

# Download musl and zlib sources:
curl -O https://musl.libc.org/releases/musl-1.2.4.tar.gz
curl -O https://zlib.net/fossils/zlib-1.2.13.tar.gz

# Build musl from source
tar -xzvf musl-1.2.4.tar.gz
pushd musl-1.2.4
./configure --prefix=$MUSL_HOME --static
# The next operation may require privileged access to system resources, so use sudo
sudo make && make install
popd

# Install a symlink for use by native-image
ln -s $MUSL_HOME/bin/musl-gcc $MUSL_HOME/bin/x86_64-linux-musl-gcc

# Extend the system path and confirm that musl is available by printing its version
export PATH="$MUSL_HOME/bin:$PATH"
x86_64-linux-musl-gcc --version

# Build zlib with musl from source and install into the MUSL_HOME directory
tar -xzvf zlib-1.2.13.tar.gz
pushd zlib-1.2.13
CC=musl-gcc ./configure --prefix=$MUSL_HOME --static
make && make install
popd

With the requirements set up, create the demo.

Build a Static Native Executable

  1. Save the following source code in a file named EnvMap.java: 
     import java.util.Map;

 public class EnvMap {
     public static void main (String[] args) {
         var filter = args.length > 0 ? args[0] : "";
         Map<String, String> env = System.getenv();
         for (String envName : env.keySet()) {
             if(envName.contains(filter)) {
                 System.out.format("%s=%s%n",
                                 envName,
                                 env.get(envName));
             }
         }
     }
 }

    This application iterates over your environment variables and prints out the ones that contain the String of characters passed as a command line argument.

  2. Compile the application: 
     javac EnvMap.java
  3. Build a static native executable by running this command: 
     native-image --static --libc=musl EnvMap

    This produces a native executable with statically linked system libraries. Run it with ./envmap.

    You can confirm the application is fully statically linked using the ldd command:

     ldd EnvMap

    The output should be “not a dynamic executable”.

Build a Mostly-Static Native Executable

With GraalVM Native Image you can build a mostly-static native executable that statically links everything except libc. Statically linking all your libraries except libc ensures your application has all the libraries it needs to run on any Linux libc-based distribution.

To build a mostly-static native executable, use this command:

native-image --static-nolibc [other arguments] <Class>

To build a mostly-static native executable for the above EnvMap demo, run:

native-image --static-nolibc EnvMap

This produces a native executable that statically links all involved libraries (including JDK-shared static libraries) except for libc. This includes zlib. Also, depending on the user’s code, it may link libstdc+ and libgcc. One way to check what dynamic libraries your application depends on is to run ldd with the native executable, for example, ldd envmap.

Frequently Asked Questions

A fully static native executable gives you the most flexibility to choose a base container image—it can even run on a scratch image. A mostly-static native executable requires a container image that provides libc, specifically glibc, but has no additional requirements. In both cases, choosing the base container image generally depends on your native executable’s specific requirements.