Question

As we can execute such executables in two ways, such as “sudo mono test.exe”, and “mono test.exe”.

Now I want to know how to detect whether this application is running as root inside the application itself.

I tried to check user name like below and see whether they equal to “root”,

Thread.CurrentPrincipal.Identity.Name

Process.GetCurrentProcess().StartInfo.UserName

AppDomain.CurrentDomain.ApplicationIdentity.FullName

The first two are empty strings always, while the third throws NullReferenceException.

Please advise if this is doable on Mono 2.6.

Answer 1

One solution is to DllImport libc and use the getuid() function. If you’re running as root, getuid() returns 0; if not, it returns some other UID:

using System.Runtime.InteropServices;

public class Program
{
    [DllImport ("libc")]
    public static extern uint getuid ();

    public static void Main()
    {
        if (getuid() == 0) {
            System.Console.WriteLine("I'm running as root!");
        } else {
            System.Console.WriteLine("Not root...");
        }
    }
}

This works fine in Mono 2.6.

EDIT: It might be better to access getuid() through the Mono.Unix.Native.Syscall wrapper class in the Mono.Posix assembly:

using Mono.Unix.Native;

public class Program
{
    public static void Main()
    {
        if (Syscall.getuid() == 0) {
            System.Console.WriteLine("I'm running as root!");
        } else {
            System.Console.WriteLine("Not root...");
        }
    }
}

Sorry, I’m not much of a Mono expert. But however you get to it, the process’s UID is what you want to know; if it’s equal to zero then you’re root, otherwise you’re not root.