PZ Server JVM Tuner
Generate optimized Java startup flags for your Project Zomboid dedicated server. Uses Java 21 (ZGC) settings — the runtime required by Build 42.
Server Configuration
Total RAM installed on the server machine
Recommended Xmx
8G
OS Reserve
8G
Java Version
21
Included JVM Flags
-XX:+UseZGC -XX:+ZGenerational
Uses ZGC with generational mode — the best garbage collector for Java 21. Reduces GC pause times that cause lag spikes on busy servers.
-XX:+AlwaysPreTouch
Commits all heap RAM upfront at startup rather than on demand. Prevents OS memory allocation delays during play.
-XX:+PerfDisableSharedMem
Disables JVM performance counters written to shared memory. Reduces unnecessary disk I/O.
-XX:+DisableExplicitGC
Prevents mods from calling System.gc() directly, which could cause unexpected GC pauses mid-game.
-XX:+UseStringDeduplication
Deduplicates identical string objects in the heap. Especially helpful with heavy mod loads that repeat many string constants.
Find the -Xmx line in ~/Zomboid/server/StartServer64.sh and replace with:
-Xmx8g -Xms8g -XX:+UseZGC -XX:+ZGenerational -XX:+AlwaysPreTouch -XX:+PerfDisableSharedMem -XX:+DisableExplicitGC -XX:+UseStringDeduplication
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