startx Doesn’t Work After Updating Debian

This is to help my future self.

Sometimes startx won’t load after updating Debian. I’ll often get no error messages in the logs, or the unhelpful message failed to set IOPL for I/O (which is a red herring). There are many reasons why startx might fail, so this issue is particularly difficult to search for.

I usually ask Harry for help.

Here’s what we did this time:

1. Boot into recovery mode
2. sudo tasksel
3. reinstall Gnome

Maybe this will help me next time.