R HOME Environment variable is not read or used in Linux (and maybe macOS)

[nmunozgarcia]

In my tests I use Xubuntu 22.04, .Net 6.0.4 (SDK 6.0.202) and two R versions (the one which comes with Ubuntu Jammy Jellyfish repositories (R-4.1.2) and a compiled by my parthner R version (R-4.2.0, the last version right now). In both R versions the results are the same.

First I had a DllNotFoundException:

System.DllNotFoundException: Unable to load shared library 'libdl' or one of its dependencies. 
In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: liblibdl: cannot open shared object file: No such file or directory

Which I solved installing the libc6-dev package and generating a symbolic link from libdl.so to libdl.so.2 (veldrid/veldrid#143)

sudo apt update
sudo apt install libc6-dev
sudo ln -s /lib/x86_64-linux-gnu/libdl.so.2 /lib/libdl.so

But now, when I execute the test, I get:
Fatal error: R home directory is not defined
on the GetInstance() Method (REngine engine = REngine.GetInstance();)

This can be fixed if, for example, in the terminal where the executable program will run, set a global variable R_HOME executing before:

R_HOME="/usr/lib/R"
export R_HOME

(As @gurza said: #122)

But this can not be the final solution because the environment variables are not working in the .Net program (and they are there for something).

The code I used for my test is the hello world example in the RdotNet project page https://rdotnet.github.io/rdotnet/tut_basic_types/

static void Main(string[] args)
{
    REngine.SetEnvironmentVariables(); // <-- May be omitted; the next line would call it.
    
    // I added this code to test if the R_HOME variable is set
    var environmentVariables = Environment.GetEnvironmentVariables();
    if (environmentVariables.Contains("R_HOME")){   // true, the variable is set
        Console.WriteLine($"R_HOME: {environmentVariables["R_HOME"]}");    // output: **"R_HOME: /usr/local/lib/R"**
    }


    REngine engine = REngine.GetInstance(); // **Fatal error: R home directory is not defined**
    // The code stops here

    ...
}

Maybe related to the #151
If the package stats is not found, the cause may be related to the fact that environment variables are not working.

[nmunozgarcia]

I see, in the Getting started zone, a content related to Updating environment variables on Linux and MacOS.

But, at least, in my test environment (Xubuntu) the routes don't exists.
I tried with /usr/local/lib as route, but this didn't work (as I expected).