Logfiles are an essential part when it comes to debugging your server and figuring what went wrong. This page contains logfiles from SpongeForge and SpongeVanilla servers including short descriptions.

Configure Logging

Sometimes plugins log messages that the server owner does not need, or the sheer number of messages hide some more important information. In other cases, plugins or the server will log debug messages that normally don’t appear in any logs. This section explains how to configure the logging. It is also possible to configure the logging in a way that splits the logs in two or more separate files. One could be optimized for the moderators that pay attention to their users’ activity/behavior and other logs could be used to monitor plugins that are important to the admins.


If you think that a plugin logs too many/few messages or on wrong log levels, please report it to its author.

The simplest way to configure the logging is modifying the log4j2.xml configuration file that will be used by Minecraft/Forge itself. You can find and extract it from the root of the forge-...-universal.jar and minecraft_server.jar. Do NOT edit the file inside the jar.

You can tell log4j2 to use the new config file by adding a start parameter to your server launch script.

java -Dlog4j.configurationFile=log4j2_server.xml -jar server.jar

The default configuration looks similar to the following example.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" packages="com.mojang.util,net.minecraftforge.server.console.log4j">
        <TerminalConsole name="Console">
            <PatternLayout pattern="[%d{HH:mm:ss}] [%t/%level] [%logger]: %msg%n"/>

        <RollingRandomAccessFile name="DebugFile" fileName="logs/debug.log" filePattern="logs/debug-%i.log.gz">
            <PatternLayout pattern="[%d{HH:mm:ss}] [%t/%level] [%logger]: %msg%n"/>
                <SizeBasedTriggeringPolicy size="200MB"/>
            <DefaultRolloverStrategy max="5" fileIndex="min"/>
        <Logger level="info" name="org.spongepowered"/>
        <Logger level="info" name="com.example.mod"/>
        <Root level="all">
            <AppenderRef ref="Console" level="info"/>
            <AppenderRef ref="DebugFile"/>


This example lacks some comments that are present in the original, make sure you read them to understand why they are there.

The Appenders section defines the output channels for the log messages. This could be a file, the console, or even a central log collection and analysis server. Read more about configuring appenders here.

The Loggers section defines filters for loggers and to which targets the messages should be forwarded to. This is usually the section you must edit if you want to mute a specific plugin in the logs. Let’s look into this a bit more:

<Logger level="info" name="com.example.mod"/>

This will limit the logs of com.example.mod to info and higher messages. Beware, this affects all output channels and also any logger that is created for a sub-package of the given path. Read more about filters here.

<Root level="all">
    <AppenderRef ref="Console" level="info"/>
    <AppenderRef ref="DebugFile"/>

This section configures two output channels. First, the appender called Console with a log level filter of info and higher, and last, the appender called DebugFile. It is recommended to keep at least one logger to a persistent target such as a file for later error search.


If you are wondering why your new plugin’s log messages don’t seem to show up: The Console’s log level is configured to be at least info by default which hides your debug messages.

If you don’t want to reconfigure the entire logging, but want to hide a certain plugin from the logs you can also use composite logging options. This can be achieved by referencing both the original logging config and your specialized config that only contains the changed logging options. The following example shows this:

java -Dlog4j.configurationFile=log4j2_server.xml,log4j2_custom.xml -jar server.jar
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
        <Logger name="com.example.logspammer" level="off"/>

In this example all logs from the com.example.logspammer package won’t be shown or saved. For debugging purposes, it might be useful to include your plugin’s log messages in the console so you don’t have to tail the debug log. This can be achieved using the following example:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
        <Logger name="com.example.newplugin" level="all" additivity="false">
            <AppenderRef ref="Console"/>


Logging affects performance. If you log too much you might lose a small amount of tps. Also remember that it will become harder to reproduce errors if there are no/incomplete logs available.

SpongeForge logfiles

SpongeForge writes several logfiles to the /logs folder located inside your server’s directory. As of Forge 1.12.2 - these are:

  1. debug.log

  2. latest.log



Only a few example lines are shown here. To read the full example log, follow this link: SpongeForge 1.12.2 - 7.1.0-BETA-3126 debug.log file

[main/INFO] [FML]: Forge Mod Loader version for Minecraft 1.12.2 loading
[main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_162, running on Windows 10:amd64:10.0, installed at C:\Program Files\Java\jre1.8.0_162
[main/DEBUG] [FML]: Java classpath at launch is:
[main/DEBUG] [FML]:     forge-1.12.2-
[main/DEBUG] [FML]: Java library path at launch is:
[main/DEBUG] [FML]:     C:\ProgramData\Oracle\Java\javapath

The example log indicates that we’re running:

  • Forge (Version 2705)

  • Java 8 64bit Update 162

  • Windows 10 x64

  • the directory Java was installed to (Line 4)


In order to run Sponge, you must be running Java 8 Update 20 or above. Older builds or newer Java major versions (like 9 or 10) are not supported.

[main/DEBUG] [FML]: Examining for coremod candidacy spongeforge-1.12.2-2705-7.1.0-BETA-3136.jar
[main/INFO] [FML]: Loading tweaker org.spongepowered.asm.launch.MixinTweaker from spongeforge-1.12.2-2705-7.1.0-BETA-3136.jar

This indicates that SpongeForge 3136 was found and loaded by Forge. For further help regarding the SpongeForge naming scheme, have a look at Reading the Download Filename.



Only a few example lines are shown here. To read the full example log, follow this link: SpongeForge 1521 latest.log

This is the output that you would see in the Minecraft server GUI.

SpongeVanilla logfiles



Only a few example lines are shown here. To read the full example log, follow this link: SpongeVanilla 1.12.2-7.1.0-BETA-54 latest.log

This is the output that you would see in the Minecraft server GUI.

Reading logfiles

If you’re unsure on how to read a common crashlog, you’ll find help here, but first we need a crashlog. For this short introduction we will just use an example crash from the Feilretting page: Example crashlog of an outdated SpongeForge build.

WARNING: coremods are present:
SpongeCoremod (sponge-1.8-1499-2.1DEV-575.jar)
Contact their authors BEFORE contacting forge

The first thing you’ll notice is a Warning that coremods are present. Nothing to worry about here, that’s not an error, just a warning to contact Sponge support, not Forge.

java.lang.NoClassDefFoundError: org/spongepowered/api/event/game/state/GameStartingServerEvent

A few lines below the actual error is found. In this case it’s a NoClassDefFoundError If you’re unsure what that means, head over to our Feilretting page. If it’s a common error, it will be listed there. If it isn’t, you can always ask on the forums for help! Make sure you provide the full crashlog.

Luckily your systems details are included at the bottom of the crashlog:

Minecraft Version: 1.8
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 515666256 bytes (491 MB) / 782761984 bytes (746 MB) up to 1847590912 bytes (1762 MB)
JVM Flags: 0 total;
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v9.10 FML v8.0.99.99 Minecraft Forge 5 mods loaded, 5 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UC     mcp{9.05} [Minecraft Coder Pack] (minecraft.jar)
UC     FML{} [Forge Mod Loader] (forge.jar)
UC     Forge{} [Minecraft Forge] (forge.jar)
UC     Sponge{1.8-1499-2.1DEV-575} [SpongeForge] (minecraft.jar)
U      Core{unknown} [Core Plugin] (Core.jar)
Loaded coremods (and transformers):
SpongeCoremod (sponge-1.8-1499-2.1DEV-575.jar)

This indicates that

  • Minecraft 1.8 with Forge 1521 was running on

  • Java 8 Update 51 (64bit version) and that

  • 2 additional mods were installed

    • SpongeForge 1.8-1499-2.1DEV-575 (which is build #575) and

    • Kjerne


Please note that the other three installed mods (mcp, FML, Forge) are required on every Forge server and necessary to run properly.

Now the following assumptions can be made:

  • maybe the plugin crashed the server

  • SpongeForge doesn’t match the Forge version: 1499 required, 1521 installed

If you want to know how to solve this, head over to our checklist on the Feilretting page.

Common errors

Head over to Feilretting to read about common errors and exceptions.