Build and package a software update

supports IoT devices across various architectures, so you’ll need GCC compilers for both x86-64 and ARM64.

Check for x86-64 and ARM64 GCC compilers by running the following commands in your terminal:

 x86_64-linux-gnu-gcc --version
aarch64-linux-gnu-gcc --version

If these commands return version information, the compilers are installed and you can continue to Step 2.

If needed, you can install the missing compilers with the following command:

 sudo apt install gcc-x86-64-linux-gnu gcc-aarch64-linux-gnu

Now that your environment is set up with the required compilers, you’re ready to write and compile your application.

To start, create a new file named helloworld.c:

 nano helloworld.c

Now we're going to write a simple C program that outputs "DigiCert Hello World!" to the console. This will form the basis of our software update. Add the following code to the file:

 #include <stdio.h>

int main() {
    printf("DigiCert Hello World!\n");
    return 0;
}

Save and close the file. In nano, press Ctrl + X, then Y to confirm, and Enter to save.

You’re ready to compile the program for both architectures to ensure compatibility with a range of devices.

Compile for x86-64 devices:

 x86_64-linux-gnu-gcc helloworld.c -o hello_x86-64

Compile for ARM64 devices:

 aarch64-linux-gnu-gcc helloworld.c -o hello_arm64

After compiling, it’s important to confirm that the application runs as expected on its intended architecture. Run each executable on the appropriate architecture:

For x86-64 systems:

 ./hello_x86-64

For ARM64 systems:

 ./hello_arm64

When executed correctly, the output should be:

 DigiCert Hello World!

You’ve successfully written and compiled a cross-platform “Hello World” application. Next, you’ll package it as a Debian package to make it deployable across your devices.

To start, create the directory structure that Debian packages require.

 mkdir digicert-hello-world-all
mkdir digicert-hello-world-all/DEBIAN

Each Debian package includes a control file to define its metadata, such as the package name, version, and description. Open a new control file to add this information.

 nano digicert-hello-world-all/DEBIAN/control

Add the following content to the control file:

 Package: digicert-hello-world-all
Version: 0.1
Section: custom
Priority: optional
Architecture: all
Essential: no
Installed-Size: 1024
Maintainer: digicert.com
Description: Sample Hello World Debian package - for demo purposes

After adding this information, save and close the file by pressing Ctrl + X, then Y to confirm, and Enter.

Place the compiled application binaries into the appropriate directory within the package structure.

 mkdir -p digicert-hello-world-all/usr/bin
cp hello_x86-64 hello_arm64 digicert-hello-world-all/usr/bin/

The post-installation script will create symbolic links to the correct binary based on the device’s architecture. This ensures that the helloworld command points to the appropriate binary for each architecture.

To check that the package structure is correctly set up, use the tree command. This command will list the directory contents to confirm your files are in place.

 tree -L 3 digicert-hello-world-all

Your output should look like this:

 digicert-hello-world-all
├── DEBIAN
│   ├── control
│   └── postinst
└── usr
    └── bin
        ├── hello_x86-64
        └── hello_arm64

Once your package structure is in place, use dpkg-deb to generate the .deb package file.

 dpkg-deb --build digicert-hello-world-all

The dpkg-deb --build command creates a .deb package from the digicert-hello-world-all directory, which can be used for local testing or deployed to compatible devices.

To install the package, use the dpkg -i command. This command installs the digicert-hello-world-all package onto your device.

 sudo dpkg -i digicert-hello-world-all.deb

After installation, run the application to confirm it executes properly.

 helloworld

If the package was installed successfully, you should see the following output:

 DigiCert Hello World!