## Developing and Running C# Programs on Linux

Recently I was asked about running C# on Linux, and I remembered that I haven't actually written a blog post on it! This is that blog post I never wrote: A beginner's guide on how to develop, compile, and run C# programs on Linux. Here I assume a debian-based system (specifically Ubuntu 16.04), but it can be just as easily adapted to work with other flavours.

To start off, you'll need to add the mono repository to your system's apt repository list. Taken from the official mono website, here are the commands to do that:

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

The more experienced may notice that although I'm installing on a, Ubuntu 16.04 system, I'm still specifying wheezy when installing mono. This shouldn't make too much of a difference - currently mono only supports wheezy upon install.

Next, it's time to actually install mono itself. This is easy:

sudo apt install mono-mcs

The above ought to install the mono runtime and compiler. If you experience issues down the line, simply install the mono-complete package instead.With this installed, you should now be able to launch compiled programs written C♯ by double-clicking them in your file manager - without any modifications. C♯ programs compiled on Windows can be run on Linux, and vice versa (this is because C♯ actually compiled into something called the Common Intermediate Language, or CIL).

If you're on a server, then you can run your programs by prefixing the executable name with mono, like this:

mono program-of-awesomeness.exe

If your program crashes, however, the output is not very helpful at all. Thankfully though there's a way to remedy that. First, make sure your program is compiled in debug mode, and then add the --debug flag when running your program:

mono --debug another-awesome-program.exe

This is all very well, but what about compiling? That's relatively easy as well. mcs is the linux version of csc on Windows, and behaves almost identically with some minor syntactical changes (read up about it by typing mcs --help or man mcs). For Visual Studio solutions, there's xbuild. Xbuild is a new-ish build too for Linux that is capable of compiling almost any Visual Studio solution file without any modifications (though there are some undocumented difficulties that you might run into as an advanced user).

To use it, first install the mono-xbuild package (sudo apt install mono-xbuild), and then, in a terminal, cd into the directory that contains the solution you want to compile, and then type xbuild and hit enter. That's it!

All this work in the terminal is cool for running C♯ programs on GUI-less boxes and servers, but it's no way to develop a larger application. Thankfully, there's a solution to that too! Monodevelop is the best C♯ IDE out there at the moment - it's like Visual Studio for LInux. It's easy to install, too - simply install the monodevelop package (sudo apt install monodevelop).

(Above: Monodevelop running on my Linux laptop. The project open here is my sprite packing tool.)

The package in the official repositories should be good enough for general use (though it's probably out of date). For the latest version with all the latest features though, you'll have to compile it from source.

Sadly this is not a trivial process. To do it you need to be comfortable with the terminal and know your way reasonably well around a Linux system. If you still want to go ahead anyway, start by downloading the latest release and follow the instructions. You'll probably find it keeps complaining about things not existing - usually a quick apt search {thing} reveals which package you need to install in order to get it to work. If you have trouble, post a comment below and I'll try to help you out.

Even without compiling monodevelop from source, it's still a pretty good IDE. It lets you create Visual-Studio-compatible solution files, and compile your code on the fly at the touch of a button.