Where do I set RAM buffer, minimum RAM, and Xms/Xmx, and what values should I use?

Where do I set Xms and Xmx?

On the Settings page, exposed as the Minimum RAM and RAM Buffer variables.

Xms (Minimum RAM) is the memory floor. RAM Buffer shapes the maximum: the value you enter lowers the JVM's usable Xmx by that much, reserving headroom that prevents out-of-memory crashes.

What RAM buffer value should I use?

300–500MB for servers under 3GB, and 1000–3000MB for 3–10GB and larger.

Pick the range that matches your server's total RAM. The buffer is the headroom that keeps the JVM from running out of memory under load.

Should Xms and Xmx be equal?

It is not required, but it is a safe and common choice for Minecraft servers.

When Xms equals Xmx, the JVM allocates the full heap up front and never has to resize it during play, which keeps memory behavior predictable and matches how most server operators run things. The one hard rule is that Xms must stay at or below Xmx.

Why does my server crash the moment it starts?

Almost always because Xms (Minimum RAM) is set higher than Xmx. Lower the minimum.

Setting the minimum above the maximum is the number-one cause of an instant crash on startup. If your server dies immediately after you touch the RAM variables, check those two values first.

How do I apply new RAM values?

Set the values on the Settings page, save, then restart the server so they take effect.

Open the Settings page, set Minimum RAM (Xms) at or equal to Xmx, set the RAM Buffer using the ranges above, save, and start from the Console.