Paper, Spigot, Folia, Purpur, Velocity, BungeeCord, Forge, NeoForge and Fabric: what each console message means and what to change. 43 errors, each with an example of the console line, the cause and the fix.
In the console
You need to agree to the EULA in order to run the serverFailed to load eula.txt
Minecraft servers refuse to start until eula.txt contains eula=true, which confirms you accept Mojang's End User License Agreement.
Links: Minecraft EULA
In the console
Can't keep up! Is the server overloaded? Running msms or ticks ticks behindCan't keep up! Did the system time change, or is the server overloaded? Running msms behind
A tick should take 50 ms (20 TPS). The server fell several ticks behind, so players see rubber-banding, delayed blocks and mobs freezing. Occasional messages during world generation or startup are normal; repeated ones mean the server is overloaded.
In the console
The server has stopped responding![Watchdog Thread/ERROR]A single server tick took seconds secondsServer Watchdog/FATAL
The main server thread was stuck on a single tick for a long time, so the watchdog printed a thread dump (and may have killed the server). Something blocked the tick: a slow plugin task, a huge redstone or entity build, a deadlock or very slow disk.
In the console
Exception in server tick loopEncountered an unexpected exceptionFailed to start the minecraft server
An unhandled error escaped the main game loop and the server shut down. Minecraft writes a crash report that names the cause.
In the console
This crash report has been saved to: pathCrash report saved to path
Minecraft saved a crash report to crash-reports/. It contains the exact error and the mods or plugins involved.
In the console
Could not load 'file'Could not load plugin 'file'Error loading plugin file
The server skipped a plugin. The lines that follow say why: it is built for another server version, a dependency is missing, the jar is corrupt, or it is not a Bukkit/Paper plugin at all (a Forge/Fabric mod or a Velocity plugin in the wrong folder).
In the console
Error occurred while enabling pluginError occurred while disabling pluginError occurred (in the plugin loader) while enabling pluginPlugin plugin v … has failed to register events for
The plugin loaded but crashed during its setup, so it is disabled. Usual causes: broken config, a database it cannot reach, or a version mismatch.
In the console
Cardinal Review[plugin] … disabling pluginA plugin switched itself off right after it started, so its commands, listeners and features are not running. Plugins do this when a startup check fails: an unsupported Minecraft or server version, a missing dependency, a broken or missing config, a database it cannot reach, or an error while enabling. The plugin prints the reason in the lines just before it disables; Cardinal Review lists that reason as its own finding when it recognises it.
In the console
Unknown dependency plugins: [deps]can't load plugin plugin due to missing dependency depsmissing dependency … [deps]missing dependency: deps
A plugin needs another plugin (named in the error) that is not installed, is the wrong version or failed to load itself, so the plugin that needs it is disabled or only partly works.
In the console
Unsupported API version versionInvalidPluginException … api-version
The plugin declares it needs Minecraft API version which is newer than this server. It was made for a newer Minecraft version.
In the console
version of plugin does not support your server version[plugin] … does not support your server versiondoes not support your server versionunsupported server version
A plugin checked which Minecraft and server version it runs on and reported that it does not support it. It may still load, but anything that relies on the server's internals (NMS, packets, inventories, entities, world data) can silently break or throw errors later. This usually happens after the server was updated and the plugin was not, or when an old build of the plugin is used on a newer server.
version in the console) with the versions the plugin supports (listed in the log line or on its download page).In the console
Ambiguous plugin name 'plugin'Two jars in plugins/ declare the same plugin name, usually an old and a new version. The server loads only one of them, which may be the wrong one.
In the console
Could not pass event event to pluginA plugin crashed while reacting to a game event. The action may still have happened, but the plugin's part of it did not.
In the console
Cannot load fileInvalidConfigurationException: reasonin 'reader', line line, column column
A config file is not valid YAML, so the plugin ignores it and runs on its defaults, or does not start. The YAML reader stopped near line (see the lines below): reason
Links: YAML validator
In the console
at com.example.listener.JoinListener.onJoin(JoinListener.java:42) ~[ExamplePlugin-1.4.jar:?]Stack traces in the log run through code from a plugin. When an error does not name its plugin, the jar in its stack trace is usually the one that caused it.
In the console
Plugin plugin generated an exception while executing taskA scheduled task (timers, autosaves, async jobs) of the plugin threw an error. Repeating tasks may spam this every tick and cost performance.
In the console
Command exception: commandUnhandled exception executing command 'command' in plugin plugin
Running a command threw an error, so it did nothing or only part of it. The stack trace under this line shows where it failed: when it runs through a plugin's jar, that plugin (named in the trace) owns the command; when it only runs through the server jar (paper, spigot, purpur), it is a bug in the server software or the command ran at a moment the server could not handle.
In the console
CommandSourceStack.getLevel() is nullA command typed in the console crashed because its command source had no world: Minecraft reads the world's game rules before it runs a command, and the console's source returned none. The stack trace runs only through the server jar, so this is the server software, not a plugin. It happens when a command is sent before the worlds have finished loading, and on early builds for a new Minecraft version where the console has no world set. The command did not run; the server keeps going.
Links: Paper builds · Paper issue tracker
In the console
Nag author(s):Loaded class … from … which is not a depend or softdepend of this pluginInitializing Legacy Material Support
The server is warning that a plugin does something discouraged: uses deprecated APIs, loads another plugin's classes without declaring it, or has no api-version (which triggers slow legacy material support).
In the console
*** Error, this build is outdatedYou are behind version behindThis server is running … (Implementing API version … ) and is outdatedOutdated server! I'm still on version
A newer build of the server software exists. Builds often fix crashes, exploits and performance problems.
In the console
Outdated client! Please use versionlost connection: Outdated client
A player's game version does not match the server (version).
In the console
/client: … lost connection: Internal Exception: io.netty.handler.codec.DecoderException: … login/serverboundPacket login/serverbound/minecraft:packet (…) was larger than I expected(ServerboundHelloPacket) was larger than I expectedFailed to decode packet 'minecraft:hello'
Something connected to the server's port and sent a login packet the server could not read, so the connection was dropped before any player joined. Repeats are shown as one finding, with each address listed once. The usual causes are a client, proxy or version-translation plugin (ViaVersion, Geyser) speaking a different protocol version than the server, or a bot or port scanner probing the server with malformed packets.
In the console
Username 'player' tried to join with an invalid sessionlost connection: Failed to verify username
The server asked Mojang to confirm a player's login (a player) and Mojang said no, so the player saw 'Failed to verify username!'. The usual causes are a stale launcher session, a non-genuine (cracked) client, a proxy in front of a backend that still checks accounts itself, or prevent-proxy-connections rejecting players whose IP changes (VPN, mobile data).
In the console
Couldn't verify username because servers are unavailableAuthenticationUnavailableException
The server could not reach Mojang's session servers to check a player's login, so players saw 'Authentication servers are down'. Either Mojang is having an outage, or the server's own network or DNS cannot reach sessionserver.mojang.com.
In the console
lost connection: Took too long to log inDisconnecting player … : Took too long to log in
A player took more than 30 seconds to finish logging in and was disconnected. Common causes: the server was lagging at that moment, a login plugin (auth, anti-bot, database lookup) was slow, the player's connection is poor, or a large resource pack or modpack handshake held things up.
In the console
Server attempted to load chunk saved with newer version of minecraft! saved > currentServer attempted to load chunk saved with newer version of minecraft
The world was opened by a newer Minecraft version (data version newer) than this server runs (older). Minecraft cannot downgrade worlds, so these chunks are refused to keep them from being damaged.
In the console
Failed to load datapacks, can't proceed with server loadErrors in currently selected datapacks prevented the world from loading
The world's data packs could not be loaded, so the server stopped. It usually happens after mods or a modpack were changed while keeping the same world (the world still lists data packs from the old mods), or when a data pack in world/datapacks has a broken file.
In the console
[DUPE-UUID] Duplicate UUID found used byKeeping entity entity that already exists with UUID
Two entities were found with the same UUID. It is usually left over from a crash, a rollback or a plugin that copies entities, and the duplicate is ignored or removed. A few lines are harmless; a flood of them can mean a duplication glitch or a plugin cloning mobs.
In the console
JsonSyntaxException: reasonMalformedJsonException: reason
A JSON file (a mod config, a data pack file, whitelist.json, ops.json or similar) has a syntax mistake: see the line. JSON allows no comments and no trailing commas, and a missing bracket or quote breaks the whole file.
In the console
Couldn't load server iconserver-icon.png in the server folder is not a valid icon, so the server list shows the default one. It must be a PNG exactly 64 x 64 pixels.
In the console
Cannot reply to EncryptionRequestPacket without profile and access tokenGeyser was asked to log a Bedrock player in to an online-mode Java server but had no Java account to do it with. Either Floodgate is not set up where it should be (or its key is duplicated), or the Java server is in online mode while Geyser's auth-type is offline.
In the console
player moved too quickly!player moved wrongly!
The server rejected a player's movement and pulled them back. Usually caused by server lag, a laggy player connection, elytra or vehicle speed, or a movement cheat.
In the console
SERVER IS RUNNING IN OFFLINE/INSECURE MODEonline-mode is false, so the server does not check accounts with Mojang. That is correct behind a BungeeCord/Velocity proxy with forwarding set up, but on a public server anyone can join as any player, including admins.
In the console
If you wish to use IP forwarding, please enable it in your BungeeCord config as wellThis server requires you to connect with VelocityUnable to verify player detailsPlayer info forwarding is disabled
The proxy (BungeeCord/Waterfall/Velocity) and the backend server disagree on how player information is forwarded, so players are kicked or appear with the wrong UUID.
In the console
Failed to save chunkCouldn't load chunkChunk file at [ … ] is in the wrong locationRegion file … is truncated
Part of the world on disk is damaged or could not be written. Common causes: the server was killed while saving, the disk filled up, or a world was copied while the server was running.
In the console
Failed to load level.datException reading … level.datlevel.dat … corrupt
level.dat stores the world's settings and spawn. If it cannot be read the world will not load, or Minecraft may create a new one.
In the console
Encountered an exception while ticking entityTicking entityEntity being ticked:
A specific mob, item, minecart, chest or machine caused an error when the server updated it. If it repeats, every restart can crash at the same spot.
In the console
session.lock … lockedFailed to check session lockThe directory … is already lockedDirectoryLock$LockException
Another server process still holds the world's session.lock file, typically a previous instance that did not shut down, or two servers pointing at the same world.
In the console
Unknown command. Type "help" for help.Unknown or incomplete command, see below for error
A command sent to the console does not exist. Often a schedule or a plugin sends a command for a plugin that is no longer installed.
In the console
Incompatible mod setMod resolution failedMissing or unsupported mandatory dependenciesrequires … of dependency, which is missing
The mod loader checked every mod's requirements and something does not fit: a dependency (listed below the error) is missing, a mod targets another Minecraft or loader version, or two mods conflict.
In the console
Mixin apply failedMixinApplyErrorMixin transformation of … failedInvalidInjectionException
A mod patches game code with Mixins and the patch no longer fits, usually because the mod is for another Minecraft version or conflicts with another mod patching the same code.
In the console
for invalid dist DEDICATED_SERVERAttempted to load class net/minecraft/client/Environment type CLIENT is required
A mod that only works in the game client (minimaps, shaders, HUD or rendering mods) was put on the server, which has no client code.
In the console
Mod File file needs language provider provider:needed or above to loadneeds language provider provider:needed or above to load
A mod (one of the mods) was built for a newer loader than the server has: it needs the loader:a newer version or above. This also happens when a mod for a different Minecraft version was dropped into the mods folder.
Paste your log into the live demo, or install Cardinal Review Lite and it will point at the line for you. Lite is free.