How to Fix “Could Not Reserve Enough Space for Object Heap”

Direct answer

Reduce -Xmx to a value your environment can actually reserve, confirm you are using 64-bit Java, and make sure the host/container has free memory beyond the requested Java heap.

Check the startup flags

A server with 8 GB available should not automatically be launched with -Xmx8G. The OS, native JVM memory, threads, direct buffers, and other services need headroom. Managed panels may also enforce a lower hard limit than the physical machine.

Confirm the Java architecture and version

java -version

Modern Minecraft server versions require 64-bit-capable environments. If an old 32-bit Java installation is accidentally first in PATH, remove it from the server startup path and use the correct supported 64-bit runtime.

Start with a conservative heap

java -Xms1G -Xmx4G -jar paper.jar --nogui

The right value depends on the server, plugins/mods, player count, and host. The example only illustrates that Xmx should be below the machine/container ceiling, not that every server needs 4 GB.

If a hosting panel still kills the process

Check the panel’s memory limit and container overhead. A startup that works from the host shell but fails inside the panel points to the panel/container environment, not the world files.

Check the actual memory limit

Run java -version and identify whether the hosting panel uses a 64-bit runtime. Check the Java launch arguments for -Xms and -Xmx rather than only the RAM slider in the panel.
On a container, compare the requested heap with the container memory limit; native memory and other processes need headroom.
Reduce an impossible heap reservation or move the server to an environment with enough usable memory; do not turn off memory limits as a general fix.

Official references

These references were checked while preparing this fix. Version-specific behavior can change, so use the project documentation for your exact release when a detail differs.

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