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Error occurred during initialization of VM Could not reserve enough space for 2097152KB object heap (Same error is The specified size exceeds the maximum representable size and Invalid maximum heap size).

You are likely missing the 64bit version of Java. It's either not installed or needs reinstalling. Want to check if it's installed? Open a command prompt and type: java -d64 -version

If it gives you an error, you don't have it installed. You can download it here (Java 8) or here (Java 11).

Paper 1.17 or above requires Java 11 (info here).

Unable to connect to the server.

As the server owner, try connecting with "localhost" (without the ""). This will only work if you are hosting the server on the same computer. Works? Great! This means there is nothing wrong with the actual server.

However if you want other people to be able to play on your server, you will need to port forward your ip. See section on Port forwarding.

Make sure port 25565 (both TCP & UDP) is allowed through your firewall or else it will Refuse the connection.

Is there a mac or linux version?

No unfortunately there isn't a version for mac. Mcss is Windows only.
Supported OSs: Windows Server (2008R2 SP1/2012/2016), Windows 7, 8 and 10

Is this 24/7?

No, it's software that runs on your computer.
Nothing like Aternos.

MCSS crashes when starting it.

Do you have .NET Framework 4.7.2 (or higher) installed?

How do I regain control of my server if mcss crashes?

To regain control of your servers you need to kill all Java processes,to do this you go to "Quick Options" > "Kill all Java processes"

Screenshot of the Kill all java processes option


This will kill ALL Java processes, not only mcss hosted Minecraft servers. This includes: * Minecraft instances * Any other program running Java or relying on Java to function

Since v11.5.0 the process name requires a different format.

Screenshot of the process name requires different format dialog

This change is required, click 'Yes' to apply the change.

Failed to set performance counters.

Screenshot of failed to set performance counters dialog

Your performance counters are corrupt. Mcss can automatically do this for you. Click "Yes" to fix it.

In case you want to do this manually:

Open a command prompt with administrator rights and execute the following commands:
cd c:\windows\system32
lodctr /R
(if the lodctr command fails, simply run it twice)

More info: Microsoft Support | How to manually rebuild Performance Counter Library values

I have this weird IP address: 2001:0db8:85a3:0000:0000:8a2e:0370:7334, is this normal?

Yes that is completely normal, that is called an IPv6 address. Most people don't have access to IPv6 yet so it's smart to share your IPv4 address instead.

There are 2 versions of the IP protocol.
IPv6: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
More info about IPv6

FUN FACT: IPv6 doesn't have port forwarding, there are no internal and external IPs. Every computer has it's own public IP.

Updating from or older fails.

Due to backend api changes version (and older) was considered End of Life (EOL) as of January 1st 2020. Update from these old builds is no longer possible, they might even break.

You will need to update mcss manually. Download the latest version from the website and rename it to mcss.exe and copy'n replace it with the existing one. (make a backup just in case)

When I click on start, the console remains empty and the server does nothing/Java is not installed.

This is because you don't have Java installed, or it is not in the PATH variable

The PATH is the system variable that your operating system uses to locate needed executables from the command line or Terminal window.

First, make sure to install Java from here. I you know you already have it, try the following steps to add it to the PATH : 1. Open an explorer window. Right-click on This PC and choose Properties. 2. On the left, click the Advanced system settings link. 3. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New. 4. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable by adding the absolute path to you Java installation (in most cases, C:\Program files\Java\jre<version>\bin). Click OK. Close all remaining windows by clicking OK. 5. If you were using a Command prompt window, you will need to reopen that.
(The above steps were adapted from

Mcss has crashed and I want to help fix it.

To help fix it, you can upload your Windows event logs and mcss logs. (please zip all the files and send them to me by email, SpigotMC or Discord)

To get the mcss logs:

Mcss logs can be found in the mcss folder under /logs

To get the Windows event logs:

Go to start and type eventvwr You can follow the other steps on screenshot below.

Screenshot of the event viewer

The UTF-8 encoding doesn't work, I really really need it to work.

The sad reality is that UTF-8 is a second-class citizen in Windows.

As of Windows 10 version 1903, you have the option to set the system locale (language for non-Unicode programs) to UTF-8, but the feature is in beta.

To activate it: * Run intl.cpl (which opens the regional settings in Control Panel) * Follow the instructions in the screen shot below.

Screenshot of the region settings window as part of the control panel

In some cases, the server needs to be started with additional parameters. E.g -Dfile.encoding=UTF-8, this varies from the server type used. More research is required on your end.

After setting this all up, this still doesn't guarantee that it will work. This just shows how bad the UTF-8 console support in Windows really is.

(sources) *, *