Troubleshooting — minecraft-launcher-lib 8.0 documentation

# Troubleshooting

Here is a quick checklist for you, if Minecraft doesn’t starts.

- Start the Version in the official Launcher

  > At first you should try to start the Minecraft version in official Launcher. If it didn’t start there, the problem is not in minecraft-launcher-lib or your code.

- Call install_minecraft_version()

  > Before you start Minecraft, you should first call `install_minecraft_version()`. This function ensures that everything is right and installs parts if needed. It should even be called, if you installed a version with a installer e.g. Optifine.

- Use the subprocess module

  > There are many ways to call a shell command in Python. Maybe your GUI Tooolkit brings it’s own function e.g. QProcess from Qt. But nor all of them supports a list of strings. To make sure this is not the problem try to start the command with `subproces.run(command)`. Do not use `os.system()`.

- Check the Java version

  > While newer versions of Minecraft has a Java runtime version in it’s client.json, older versions don’t have it. Some older versions requires a older Java version. Make sure to launch this old versions with the right Java version. Check out the command module documentation to learn how to set the Java version.

- Check your JVM Arguments

  > If you use custom JVM Arguments, make sure all of them start with `-` and not a other char e.g. a whitespace.

If all of the steps above failed, please fill a Bug Report.