Error Codes › Could not reserve enough space for object heap

Could not reserve enough space for object heap

COAL-003 · Couldn't reserve heap space

The JVM refused to start because it could not reserve the heap you asked for. Why this differs from an out-of-memory crash, and how to pick a size that starts.

What it looks like in the log

Error occurred during initialization of VM
Could not reserve enough space for 8388608KB object heap

What it means

This happens before Minecraft even loads. The JVM tries to reserve the whole heap up front, the operating system refuses, and Java exits instantly. Note the difference from COAL-001: there the server ran and later filled its heap, here it never started because the heap could not be handed out in the first place.

How to fix it

Lower the allocation to something the machine can actually spare. On 8 GB of RAM, ask for 4-6 GB, not 8.
Close other memory users - a Minecraft client on the same machine easily takes 2-4 GB by itself.
Check you are on 64-bit Java. Run java -version; if it does not say 64-Bit, that is your ceiling, and no amount of free RAM will get you past roughly 1.5 GB.
On a VPS, check the plan's real memory. A 2 GB instance cannot host a 4 GB heap even though the numbers look close.