How can I install a linux service from the service itself?

Question

I'm not a specialist in Linux, so sorry if my terminology is not 100% correct. I have an embedded device running Debian. The device runs the Node.js webserver. This Node.js application is bundled together with the Node executable and packaged as a .deb file. The package defines a service (daemon?) by including init.d script. So in order to update the application I only have to type "dpkg -i my-service.deb". The Node.js application can upload debian packages (.deb) and store them in a temp folder.

The question: how can I update the service (node executable + node application) from within the node application itself?

... if I call child_process.exec("dpkg -i new-version-of-my-service.deb") it first stops the service and then nothing happens.

Answer 1

Here is how the problem was solved:

function update_self(deb_package_filename) {
    var fileToInstall = path.join(upload_dir, deb_package_filename);
    var out = fs.openSync(path.join(upload_dir, 'out.log'), 'a');
    var err = fs.openSync(path.join(upload_dir, 'out.log'), 'a');
    var child = spawn("dpkg", ["-i", fileToInstall], {
        cwd: upload_dir,               // working directory
        detached: true,                // detach from the parent process group
        stdio: [ 'ignore', out, err ]
    });
    child.unref();
}

The child process is detached from the caller and therefore even when the parent process gets killed the dpkg process still runs.