How to write a display manager

Whenever I come across some topic of piece or software I don’t completely understand, I always want to try writing it. When I was in high school, operating systems and compilers were two concepts that I tried to understand but couldn’t completely get a grasp of just from reading books or articles online. That’s why I ended up writing both of them. I’ve been curious about how display/login managers and window managers work in Linux now for a while now. There are some tutorials on how to write a window manager online, but when it comes to display managers there’s absolutely nothing. That’s why I tried to write my own display manager and wrote this tutorial so you can write your own as well.

I’ll be writing this in C, but the concepts apply to any language as long as the language you’re using has all the necessary libraries. You can find my final code on Github (this is the tutorial branch, which follows this tutorial more closely), and you might also find the SLiM display manager a useful reference as well. The SLiM website (which hosted the code) went down recently as the project is no longer maintained, so I’ve linked my mirror of the project above.