6 min read
How to Read Minecraft (and Lunar Client) Crash Logs

Reading logs isn’t rocket science. It’s not some mystical skill reserved for developers. At the end of the day, it’s just about paying attention to what’s in front of you.

When Minecraft crashes — whether you’re using Lunar Client, Forge, Fabric, or any other loader — the log file is your first (and often only) clue to what’s going wrong.

Most logs fall into two categories:

These happen when a mod you (or Lunar) added is breaking something. In the case of Lunar Client, it’s either a mod you’re adding causing issues with Lunar’s code, or conflicting with a bundled mode. Other than that, mods can also conflict with each other, even if you’re using vanilla fabric, and not Lunar.

In these cases, your job is to scroll until you hit the actual error. You’ll usually recognize it from patterns like:

  • [error] (or any sort prefix that indicates that this specific line is an error)
  • Caused by:
  • Critical injection failure
  • Failed to boot Minecraft

For Lunar specifically, you might also see:

  • An error occurred while launching Lunar Client
  • [Genesis] Failed to transform
  • [Genesis] Failed to apply

Once you spot these, keep in mind: the last relevant error before the crash is usually the one that matters. Not always, but often.

Here’s a quick example:

[error] Caused by: org.spongepowered.asm.mixin.injection.throwables.InjectionError: Critical injection failure: Constant modifier method lunar$editFeedbackConstant(Ljava/lang/String;)Ljava/lang/String; in mixins.meta.lunar.modmenu.v1_21_0.json:IOHCRIOROICRICIICHRHCCORHROOCO from mod (unknown) failed injection check, (0/1) succeeded. Scanned 1 target(s). No refMap loaded.

That first line is the jackpot. It literally tells you:

mixins.meta.lunar.modmenu.v1_21_0.json

Translation? the modmenu mod caused the crash.

If two mods (or a mod and Lunar’s own code) try to modify the same thing via mixins, you’ve got a mixin conflict. That’s also a guaranteed crash. Wait — what’s a mixin? Mixins basically allow mod developers to modify the game’s code without having to change it directly. Mods inject mixins to change things they normally wouldn’t be able to.

“Their primary use case is modifying existing code in the base game, whether it be through injecting custom logic, removing mechanics, or modifying values.” (from the fabricmc docs)

These aren’t about mods at all. They’re about the environment the game is running in. For these, you’re often looking for specific, repeatable log lines. Once you’ve seen them a few times, you’ll know them instantly — no need to read the entire log every time.

Examples:

  • Outdated AMD drivers

If you’re using an AMD graphics card and your drivers are old, Minecraft can run into issues. If you’re on Lunar Client and this happens, you should be able to spot atio6axx.dll in your logs. Otherwise, the behavior is going to be different; You’ll notice a log that’s almost empty, without any information in it. As if the game has totally refused to launch. You’ll then have to look for log files inside your instance’s folder that are named starting with: hs_err_pid

hs_err_pid logs indicate a Java Virtual Machine (JVM) crash. These crashes often happen when Minecraft runs out of memory or has issues with graphics drivers

What to do:

  • Go to AMD’s official site, download the latest drivers for your GPU, and install them.
  • If you’re on a laptop with both integrated and AMD graphics, make sure Minecraft is actually using the dGPU in your system’s graphics settings.
  • Corrupted Lunar native files

Lunar Client has its own set of jar files — libraries the client uses to run. If one of these is corrupted, the game will most likely crash.

What to do:

  • Close Lunar completely (including from the system tray).
  • Go to the Lunar Client directory (on Windows it’s usually in %userprofile%/.lunarclient) and delete the jre and offline folders.
  • Restart Lunar — it will automatically re-download fresh native files.
  • Corrupted game-directory files*

The game’s own files (separate from Lunar’s special ones) can also get corrupted, especially if you’ve been moving versions, installing mods, or had a system crash while the game was running.

What to do:

  • Close the game (and Lunar if you’re using that) completely.
  • Go to %appdata%
  • Rename .minecraft to .minecraft1 or anything else.
  • Relaunch the game — it will create a new .minecraft for you.
  • You can now move your worlds/packs/etc. to the new one!

This solution assumes that you’re using the default game directory. If you’ve changed it in your launcher’s settings, simply set it on another directory and that’ll be it!


Pre-launch Crashes (Lunar-only)

These crashes.. are not even crashes. The launcher refuses to launch the game, and throws an error. These are the ones you see often:

  • EBUSY → Another process is still running and blocking launch. Restart your PC.
  • EACCES → Permission issue. Close Lunar completely (Task Manager or system tray) and run as Administrator.
  • Connection errors → “Failed to download X” or HTTP status codes like 403. That’s a network issue.
  • Unexpected error → Usually mod compatibility, corrupt Lunar files, or corrupt game files — in that order of likelihood. It can be caused by anything.
  • Memory allocation errors → Almost never the real problem. Save it for last.

Final Note

When reading logs, don’t overcomplicate it. Scan for obvious errors, and learn to recognize repeated patterns for common issues.