Bad preferences have become a superstition in the X-Plane community.  If anything goes wrong, the first thing anyone says is “delete your preferences”.  This often “fixes” the problem – in that it undoes all of your careful settings and changes about 100 different things, one of which changes enough behavior to fix the problem.  It’s the medical equivalent of curing the common cold by transplanting every single organ.

Of course, every now an then the preferences file is the problem.  It turns out that X-Plane 9.6x and 9.31 use the same version ID for the binary preferences file, and yet they use different binary preferences file formats. This was a screw-up on our part, and the result was a hang on start for 9.6x users if they had their old 9.31 preferences laying around.  In this case, nuking preferences really was the problem.  (Thanks to Andy for getting me the files to see this “in the lab”!)

Send Me Your Preferences!

What is frustrating about the 9.31/9.61 preferences bug is that people have known about it forever, and yet I only received a real bug report about it this week.  Part of the problem is how people cope with these bugs: by deleting their preferences.

Don’t delete your preferences! Once you delete the preferences files, they are gone!  If there was something wrong with them, we’ll never know.

Deleting your preferences is like burning all of your belongings when you get a cold: the Doctor won’t know what bacterium or virus you have because you destroyed every instance of it!

You don’t have to delete your preferences.  You can simply move them out of the preferences folder onto your desktop. This has the same effect as deleting them: X-Plane will not find them in the new location, and will start up with its default settings.

What if moving preferences fixes the problem?  Well, now you have two sets of preferences: the old “sick” preferences on the desktop that cause a problem and the new “rebuilt” ones that X-Plane made when you re-ran.

At this point you can now send me a bug report.  It might go something like this:

You: Hey Ben, I was getting a crash on start.  I moved my preferences files out to the desktop and it fixed it.  Here are the bad preferences and here are the good ones, in two zip files.

Me: Thank you!  That’s great!  I will look at the two sets of preferences to see what changed.  If there’ a sim bug I can identify it and find it.

You: So…do I get any kind of reward?

Me: Only the good feeling of knowing you’ve helped your fellow X-Plane users.

You: Screw you! I’m going to go use Google Earth Flight Simulator.

Okay, that didn’t go quite as well as I had hoped.  But my take-away point is this: if there is a real problem with the preferences system, such that deleting preferences is necessary, we want to look at the files and fix it in the sim!  In the long term this will lead to less need to delete preferences, which will save a lot of users a lot of re-doing settings.

Why Do Preferences Files Matter?

Why does moving your preferences files out of the way (so X-Plane can’t find them) sometimes help?  There are a few causes that I’ve seen:

  1. Incompatible or corrupt binary files.  Sometimes the preferences files actually contain junk, although this is rare.  In some cases, we don’t handle the preferences file version change and we need to fix the version check code (this is what we’re fixing in 970).
  2. Sometimes a single particular setting is problematic for a particular machine.  For example, your machine might have a driver problem that causes it to crash when “per pixel lighting” is on.  If you remove the preferences and the default is to have that setting be off, then you “fix” the problem.  In this case, a comparison of the “bad” preferences with the default ones can reveal settings that might be the problem.
  3. Sometimes settings can be set while you fly, but cause problems when the sim starts with the settings turned on.  This is rare, but with tweaky graphics drivers we sometimes do see this behavior.  Sometimes a setting takes effect on restart, so it’s not until you restart with the new setting that the preferences file causes problems.

Either way, having the “bad” preferences to inspect is critical to catching any one of these cases!

About Ben Supnik

Ben is a software engineer who works on X-Plane; he spends most of his days drinking coffee and swearing at the computer -- sometimes at the same time.

3 comments on “The Cult of Bad Preferences

  1. All these posts lately, sure do bring a smile to my face. You always seems to put a joke in somewhere. I am not sure if i come here for the cool info you give out, or to just get a laugh, but whatever it is, thank you so much.

    1. Agreed!

      I think I speak for us all when I say, “Thank you for the frequent updates, Ben!” And yes, that goes for the puns, too. 🙂

      Blessings, Patrick

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