If the server refuses to start or crashes on boot, the problem is often a Java mismatch. In this guide you will learn how to pick the right Java for your mods, set it in SquidServers, and fix common errors.

Check the pack or mod’s Java requirement

Many packs list a required Java version on their page. If a specific version is listed, use that. If nothing is listed, Java 21 is a safe default for many modern setups. Some older mods need older Java. Always follow the mod’s note first.

Set Java inside SquidServers

Open SquidServers and let it detect your installed Java versions. Pick the version that matches your pack or mod list. If you have multiple Javas, check the path shown to make sure it points to the right one.

Fix common errors fast

If you see “unsupported class file version” in the log, your Java is too old or too new for that mod set. Switch Java and try again.
If you see missing dependency errors, add the listed library mods.
If the crash started right after adding one mod, remove that mod and test again.

Keep versions aligned

Match three things every time. Java. Loader. Minecraft version. When all three line up with your mods, SquidServers will start cleanly. When in doubt, test on a copy of your world so you do not risk your main save.