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Custom Java startup parameters for Minecraft and Project Zomboid
For Minecraft and Project Zomboid, you can enter custom Java startup parameters, for example to load a Java agent or set a system property. RAM and CPU cores are not included. They depend on your tier and are set automatically at startup.
Entering parameters
- In the customer portal, open your server and the card „Einstellungen“ (Settings).
- Enter the parameters in the field „Java-Startparameter“ (Java startup parameters), separated by spaces.
- Save the changes. The parameters take effect from the next server start and are kept after game updates.
The customer portal rejects invalid parameters when you save. A maximum of 30 parameters with a total of 1,500 characters is allowed.
Allowed parameters
| Type | Example | Note |
|---|---|---|
| Java agent | -javaagent:ZombieBuddy.jar |
The file must be located in the data folder of the server. You can upload it from Flex M in the file manager or via SFTP. |
| System property | -Dname=value |
Names starting with java., jdk., sun., user., log4j or deployment. are not allowed. |
| -XX flag | -XX:+UseStringDeduplication |
Only the flags from the following list. |
Permitted -XX flags
ParallelRefProcEnabled, DisableExplicitGC, UseStringDeduplication, PerfDisableSharedMem,
UnlockExperimentalVMOptions, OptimizeStringConcat, ZProactive, MaxGCPauseMillis,
G1ReservePercent, G1MixedGCCountTarget, G1MixedGCLiveThresholdPercent,
G1RSetUpdatingPauseTimePercent, SurvivorRatio, MaxTenuringThreshold, ZUncommitDelay, ZCollectionInterval.
In addition, UseZGC and ZGenerational for Project Zomboid, and UseG1GC for Minecraft.
Not allowed: RAM and CPU
Settings for RAM and CPU such as -Xmx, -Xms, -Xss, -Xmn or -XX flags for heap, threads and CPU cores are blocked. The RAM is determined by the tier. The overview is available under Tiers and prices. You can change the tier at any time in the customer portal.
Example: ZombieBuddy for Project Zomboid
ZombieBuddy loads Java mods for Build 42. Upload the file ZombieBuddy.jar to the data folder and enter -javaagent:ZombieBuddy.jar=policy=deny-new as a Java startup parameter. You decide in the customer portal for each mod which Java mods are loaded, as described in Setting up Java mods with ZombieBuddy.
Frequently asked questions
- Why can I not set -Xmx?
- RAM and cores are part of the tier. The server sets them accordingly at startup. If you need more, switch to the next tier.
- Do the parameters still apply after a game update?
- Yes. The server carries them over after every update.
- Why is my parameter rejected?
- The parameter is not on the list of allowed parameters, or the specified JAR file is not in the data folder of the server.
See also: File manager for game servers Setting up SFTP access How much RAM does a Minecraft server need?