How to Install Mono on Ubuntu 20.04

Mono is a platform for developing and running cross-platform applications based on the ECMA/ISO Standards. It is a free and open-source implementation of Microsoft’s .NET framework.

This tutorial covers the steps required to install Mono on Ubuntu 20.04.

Prerequisites #

The instructions assume that you are logged in as root or user with sudo privileges
.

Installing Mono on Ubuntu #

Mono is not available in the standard Ubuntu 20.04 repositories. We’ll install the Mono packages from the official Mono’s repositories:

1. Install the dependencies necessary to add a new repository
   over HTTPS:

   sudo apt updatesudo apt install dirmngr gnupg apt-transport-https ca-certificates software-properties-common

2. Import the repository’s GPG key:

   sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF

   The output should look something like this:

   gpg: key A6A19B38D3D831EF: public key "Xamarin Public Jenkins (auto-signing) <[email protected]>" imported
   gpg: Total number processed: 1
   gpg:               imported: 1

3. Add the Mono repository to your system sources’ list:

   sudo apt-add-repository 'deb https://download.mono-project.com/repo/ubuntu stable-focal main'

4. Install Mono:

   sudo apt install mono-complete 

   mono-complete is a meta-package that installs the Mono runtime, development tools, and all libraries.

5. The installation may take a few minutes to complete. Once completed, verify it by typing the following command which will print the Mono version:

   mono --version

   At the time of writing this article, the latest stable version of Mono is 6.8.0.123.

   Mono JIT compiler version 6.8.0.123 (tarball Tue May 12 15:11:57 UTC 2020)
   Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
       TLS:           __thread
       SIGSEGV:       altstack
       Notifications: epoll
       Architecture:  amd64
       Disabled:      none
       Misc:          softdebug 
       Interpreter:   yes
       LLVM:          yes(610)
       Suspend:       hybrid
       GC:            sgen (concurrent by default)

That’s it, Mono has been installed on your Ubuntu machine, and you can start using it.

Getting Started with Mono #

To ensure that everything is set up correctly, we’re going to build a Hello World program that prints the classic “hello world” message.

Open your text editor
and create a file named hello.cs with the following content:

hello.cs

using System;

public class HelloWorld
{
    public static void Main(string[] args)
    {
        Console.WriteLine ("Hello World!");
    }
}

Use the csc compiler to build the program:

csc hello.cs

The command above will create an executable named hello.exe.

Run the executable:

mono hello.exe

The output should look something like this:

Hello, World

To execute the program only by typing its name, set an executable flag
:

chmod +x hello.exe

You can now run the hello.exe file by typing:

./hello.exe

Conclusion #

Installing Mono on Ubuntu 20.04 is a relatively straightforward process, and it will take you only a few minutes.

If you hit a problem or have feedback, leave a comment below.