Minecraft Forums

1. Part 1: Introduction
• Why does Minecraft crash?
• Minecraft didn't crash, it only blackscreened. What Do I do?
• The META-INF folder
2. Part 2: Getting a crash report
• Minecraft output
• Crash txt files
• Command line
• McPatcher
• Bat script
3. Part 3: Reading the crash report
• Crash report structure
• Header
• Stack Trace
4. Part 4: Common crashes
• java.lang.NoClassDefFoundError: ...
• java.lang.NullPointerException
• Block ID conflict
5. Part 5: Posting Guidelines
• Checklist
• Posting

Note: This topic is not for you to post your crash reports. This is for you to understand and hopefully fix your crashes yourself. As a final options you should always post the crash to the mod responsible for the crash (the final section of the topic suggests what should be included). I will not be fixing your crashes

Why does Minecraft crash?

In my experience there are a couple of main reasons minecraft crashes

1. Improper installation of a mod or API
2. Incompatibilities between mods
3. Some sort of bug in a mod
4. Pre-existing bug in minecraft

There can be other "fringe" cases of crashes (eg faulty hardware or not enough RAM) but the above will cover 99% of crashes encountered.

Now I just want to say, please don't "blame" anyone for a crash. If it is due to an error in the modder coding (eg 2 or 3) cut them some slack. Most modders are not professional coders, they make mods for fun. If it is due to 1 (i.e. you made a mistake) just take a breath and re-read the installation instructions for both the mod and any APIs (as well as the rest of this guide).

Minecraft didn't crash, it only blackscreened. What Do I do?

I want to start with the TL;DR version black screen = crash.

Sometimes rather than coming up with a nice little crash report, Minecraft will just show a black screen (Possibly flashing up "Saving Chunks" first). This is also a crash, and you should follow Part 2 of this guide. Crashes are generally caused by either exceptions or errors. These may or may not be caught by Minecraft's internal error logger. If the error logger does catch it, you will be displayed with the minecraft crash screen, if not just a black screen. There are ways to obtain the crash report as detailed in Part 2 below.

The META-INF folder

I just want to digress a bit to discuss what the META-INF folder is. Essentially all you need to know is this needs to be deleted if you want to mod minecraft. If you don't really care why then feel free to move to the next section. If you are curious, read on.

A java jar file is just a zip file with an optional META-INF folder. Because jars are not just a collection of .class files and resources, extra information is sometimes required (or desired) by application developers. The META-INF folder is a place to store package and extension configuration data, including security, versioning, extension and services. In Minecraft the security is the reason it must be deleted. The META-INF contains a file called "MAJONG_C.SF". This file contains a little code for each file within the jar which can be used to check if any file has been modified or corrupted. Therefore this file must be deleted to prevent the security check if you want to edit any of the files within the jar.

Now this is a very basic description of the META-INF folder as I was trying to make it as easy to understand as possible. If you are still interested look up the .jar file documentation on the java website

Crash txt files

Both Modloader and Minecraft Forge try and output any crash reports into folders. This should be the 1st place to check. Now you do have to be carefully because occasionally I get people posting the contents of one of these files that doesn't actually contain the crash log (i.e. not helpful). Don't worry if this is the case, I will detail in Part 3 how to read the crash report meaning you will know if you have the wrong file. If this is the case, try another method described below.

Note: When I refer to directories in this section, everything is relative to the .minecraft directory. I will assume if you are installing mods you already know how to find it (It is dependent on your operating system)

BroTip: In windows the directory can be easily found by pressing the windows key + 'R' and typing "%AppData" (without the "'s) in the run dialog and pressing Enter. This should bring up an explorer window withe the .minecraft directory somewhere near the top.

Modloader
Modloader generally tries to output it's crash reports in a file called "Modloader.txt". The file should be located in the ".minecraft" directory. This will only be from the last run of minecraft (i.e overwritten on each run). This obviously will only be present if you have modloader installed (Minecraft Forge has a different way of reporting crashes).


BroTip: If posting from the Modloader.txt file make sure it actually contains a crash, I couldn't tell you how many times people post me the contents of their Modloader.txt file when there is no crash in there.

Minecraft Forge
There is a folder that Minecraft Forge creates devoted to crash logs. The folder is located in the .minecraft directory and is called "crash-reports". Each crash will display the date/time of the crash as well as the describing if the crash was in the client or server. Another thing that should be mentioned about this file is that it is set out differently to other crash logs. The Forge crash logs will have the stack trace at the top and the header information below it (they also contain a "witty" comment).

BroTip: Try to avoid opening the forge crash logs with notepad on windows. Notepad does not recognise the newline character used (because it is quite crappy). Try opening it with wordpad instead (right click, go to open with and selected wordpad or "other programs" and find it).


Command Line

Now because you are hear I am going to assume you are not very technically minded, therefore using the command line may scare you a little. I want to start with, don't be scared, the command line is a very powerful tool. Of course there are more "user friendly" ways, but the command line is quick and does not require downloading on any extra files. Now these do depend on your operating system so only read the relevant one below

Windows

1. Open the command prompt by pressing windows key + 'R' and typing cmd in the run dialog (and press enter)
2. Type "cd %AppData%" and press enter
3. Type "cd .minecraft" and press enter
4. Enter the following command

java -Xms1G -Xmx1G -cp Minecraft.exe net.minecraft.LauncherFrame



Brotip This can be pasted by right clicking on the command line window and pressing paste

5. Login, start minecraft & re-create the crash. The crash should be displayed in the command line window.
6. Highlight the crash report in the window, right click and press copy.

Note: for this to work you must have java as an environment variable. Read more here

OSX
Warning I do not have an Mac computer so I have not tested this and do not know how user friendly the method is. These instructions are from the Minecraft wiki page

• Go to Macintosh HD/Applications/Utilities and open Console.app
• Run minecraft and when it crashes the java log will be added to the console, which you can then select and copy

Linux

• Open a terminal (on distributions such as Ubuntu/Linux Mint, this is done with Ctrl + Alt + T)
• Run

java -Xms512m -Xmx1024m -jar minecraft.jar 




• Watch the console output. You can select and copy it after making the game crash.

Note: Your current directory MUST be wherever the minecraft.jar file is. If you are using linux I am going to assume you know at least basic command line functions.

MC Patcher

MC Patcher can be a great tool for obtaining crash reports (personally I don't like it for it's HD patching capabilities because i don't like it's methods but that's just me). Start by downloading mcpatcher from here

This is what the default interface should look like.



For this purpose I recommend unticking all boxes before proceeding and DO NOT hit patch. Hitting patch will make MCPatcher run through it's patching routine, problem is this has been known to interfere with the proper running of some mods including Minecraft Forge. Pressing "Test Minecraft" (Red Arrow) will launch minecraft in offline mode. Recreate the crash. The output will be displayed in the "log" tab (Red arrow in the picture below)



Now the great thing about mcpatcher is that it actually tries to give you the deobscurificated class/method/field names in the crash report. This can be an unbelievable help to the author of the mod if you have found a new bug or incompatibility.

Bat script

Windows Only

I have also developed a bat script to assist in the gathering of crash logs. Unfortunately I found a bug in it. I will correct the bug and upload it at a later date.

Now right away from this we can see that this user is using the 1.3.2 version of minecraft, has minecraft forge installed, is using Mac OS X (64 bit) is using java 1.6, has 2 mods other than Minecraft Forge/FML both of which were loaded successfully (in this case they are both 2 parts of the same mod). Furthermore because the author (me) is so awesome and put the version of minecraft required in the zip name, we can tell that he is using a mod that is designed for the minecraft version he is using. So far everything looks great.

Brotip: If you are super worried about privacy and do not want to post your username, remove that section of the crash report or start it out like I did above.


The Modloader styled headers are slightly different, However I do not have access to one on hand right now (I only mod with forge) but they also generally show similar information. Crashes may occur without either modloader or forge (jar mods only or bugs in the vanilla game), again these should show the minecraft version/java version/os etc but for obvious reasons will not show loaded mods.

Stack Trace

The stacktrace is the main technical part of the crash log.

Here is an example (in this case it is the other half of the header posted in the above section)

Stack traces are always printed from most recent to the least recent step in the trace (kind of like your browser history is ordered from most recently visited sight to the site you viseted a long time ago). The first line will describe the type of error. Take note of this, it can help you diagnose most of the problems. In the example above this is

java.lang.NoClassDefFoundError: paulscode/sound/SoundSystem

I will go into more detail about this error in the next section as it can be a common crash.

Brotip: When dealing with this remember "Google is your friend" googling the 1st part of the error "java.lang.NoClassDefFoundError" can help you diagnose the general cause quite easily. Going to the 4th result (which is the java documentation tells us that this means "Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.". In other words something that minecraft or the mod thinks is there is not actually there. This could be improper installation or a corrupted file, but right away we know quite a bit about the error.


Under the error name is a whole heap of at (classname).(method).... These can also be quite important to modders as it gives us a way to backtrack through the error to hopefully find the root of it. Again the most recent is at the top and least recent is at the bottom. This can be handy for those even without a background in programing. Sometimes you can find the culprit quite easily by scanning through the trace. For example if you see "mine_and_blade" in any part section, it is a good chance that the Mine & Blade mod is likely the source (In one way or another) of the crash.

For those who have a bit of programing experience what the above trace tells us is that the method a in ayq class had an error, it was called by the a method in the Minecraft class which was called by the next one down and so forth.


Now when we see a "Caused by" that means what we have is a "Chained Exception". This is important because it is often the case that one of the fundamental exceptions underlying the last encountered exception is the real culprit that must be appropriately addressed. So in other words, these secondary exceptions may be just as important. I can not tell you when they are and when they are not because it really depends on the particular error report.

java.lang.NoClassDefFoundError: ...

I wanted to start with the error I have been using in the examples above. Here is the full crash report

A NoClassDefFoundError is thrown whenever a java program can't find a particular class that it thinks should be there. The class will be displayed after the ':' as well as the package/folder it is contained in. In the example above that means that the class that cannot be found is called SoundSystem and it is located in the paulscode/sound package.

There are 3 main reasons this can occur listed below

1. You have not installed a required dependency. This is probably the most common cause of this error. Most of the time you can guess the missed dependency by looking at the classname/package. One common one I have encountered is when people forget to install PlayerAPI. In this case the crash will display java.lang.NoClassDefFoundError: PlayerBase. Always go back and make sure you have installed all dependencies for a mod
2. The next most common reason I have seen for this error is due to a corrupted file. This happens occasionally while downloading mods. Just try and re-download the mod or API and try again.
3. The mod auther has not packaged a particular class file. This will generally mean that part of name/package will have something to do with the mod. Now this is more rare than the other 2 above because if a modder does make a mistake such as this they will generally address it quite quickly. Also remember that your 1st assumption should be a corrupt download (2 above) so try to re-download the mod 1st.

Now the error posted above was actually due to a corrupted download of Minecraft Forge. After the user re-downloaded Forge everything worked again.

java.lang.NullPointerException: ...

The dreaded null pointer exception. The most common cause of this doosy is due to modder error. It can also be caused by incompatible mods or knock on effects from other errors but generally its because of dodgy code. Null pointer exceptions occur when java tried to access an empty object. Because the object doesn't actually exist, java will have a cry and break down. Mostly this can't be fixed by anyone other than the author of the mod(s) in question.

The only recommendations I can say for this is to

1. Try and work out the mod causing the error by looking at the stack trace.
2. Make sure you don't have mods that are known to be incompatible installed
3. Check the forum page to see if anyone else has already posted this error, if so there may already be a solution in the works and there is little point in re-posting the same error (maybe just a "I got the same error as x") but there is really no point in posting the exact same error log

Sorry I don't have an example right now, but these errors can be quite varied. If anyone really wants one I will find one later (or generate one myself) and post it.

Block ID conflict

This happens when you install a mod that is trying to use the same block ID as another mod. They can be identified by the first error being java.lang.IllegalArgumentException: Slot xxx, where xxx is a number.

Here is an example

These are generally easy to fix, most mods have some sort of config file (generally in the config directory of the .minecraft folder) that is generated the first time a mod is loaded. A mod can customise the block/item ids used in this file. So your best bet is to find the offending block id and change it in one of the mods and try again. You may have to try a number of times to find free block ids. Also minecraft does have a limited number of block IDs available for vanilla/modloader the limit is 255 (the 1st ~ 150 or so are taken up by normal blocks) while Forge has increased this to a bit over 4000. I believe vanilla will increase this to 4000 but I don't think it is currently implemented.


Just a note, conflicting Item ids will not cause a crash, but these can be identified by items randomly changing to another item on startup/crafting.

Brotip 1: A tool such as TMI can be used to help identify free block ids. The TMI side bar interface displays the block id used by whichever block you are overing over.
Brotip 2: If you can help it, always change the block ID of the most recently installed mod. Blocks in your world will also change.

1. Obtain the crash report
2. Make sure it is actually a crash report (i.e. has a java stack trace)
3. Do basic diagnostics yourself (read the thread)
4. Make sure it is not one of the common crashes seen here
5. Identify the mod causing the error
6. Try the mod on a fresh jar with only the required APIs, this will help determine if the problem is caused by an incompatability.
7. Read the Troubleshooting/FAQ section of the Mod page to make sure it is not a common problem that can be fixed
8. Read the known bugs on the Mod page to make sure your are not-reposting a known bug
9. Read the Incompatible mods section to make sure that you are not using incompatible mods
10. Read the last page or two to make sure someone hasn't recently posted the same report (no point in reposting unless you have more information to add)
11. Do a quick search on the forum topic using the most recent error (eg java.lang.NoClassDefFoundError: paulscode/sound/SoundSystem) as someone else may have already posted the same error a while ago and it has since been solved.
12. Post your error using the guidelines below.

Always remember that posting the error should generally be your last resort. You will generally solve the problem quicker yourself as a modder is not always online to answer questions. You may not get a response for a few days and you can't blame the modder for this. It is therefore in your best interest to at least try and solve it yourself.

Posting Guidelines

Now before I start, if a modder has another way they like to describe an error report follow theirs. This is just a suggestion.


When posting an crash report having as much detail as possible is the key. If you write stuff that's not needed, who cares? But not having enough detail can be very annoying for those trying to help.

At minimum you want

1. The crash report (the most important part)
2. A detailed description of your problem (when did it crash, what were you doing in game etc). Again the more details the better, even if you don't think they are relevant. Better to be safe then missing an important detail.
3. A list of mods APIs and patches used, sometimes this may not be needed as the might be displayed in the crash log, however sometimes not all are displayed. This includes APIs such as Minecraft Forge & PlayerAPI as well as patches like McPatcher or jarmods like Optifine.
4. Generally the OS that you use is not needed, java is generally cross platform. Although some mods may not like some OS because of the way certain features are written. Use your best judgement on this (especially considering it may already be in the crash report).
5. Any other mod specific information that might be required. This one really depends on the mod you are using and will mainly apply to very special cases\
6. Be Polite, as a modder I am much more likely to be more helpful to someone who has both been polite and actually tried to do a little homework (i.e stuff on this post) then to someone who as not.

Brotip: Crash logs can be quite long. Always put them in a spoiler as this will tidy up the post a bit. A spoiler can be made like this

[spoiler]
Paste crash log here
[/spoiler]

If you do do this it might also be a good idea to also write what the crash was somewhere outside of the spoiler so it can be search for by other users easily.


An example post might look something like this

ExtrabiomesXL is a collaborative open source mod for Minecraft which adds new biomes and an assortment of natural blocks and items that enhance gameplay and make exploring fun and interesting. Keep up-to-date on the latest development news and general interest regarding ExtrabiomesXL on http://extrabiomes.com/. ​The official ExtrabiomesXL wiki is the best place to read any kind of information regarding ExtrabiomesXL.


Prerequisite
ExtrabiomesXL 3.16.3 was tested using Minecraft Forge 10.13.4.1481, which can be found here.

Downloads

ExtrabiomesXL Universal 3.14.1 backported to MC 1.5.2

ExtrabiomesXL on CurseForge;quot;]


• Google Drive folder of all ExtrabiomesXL versions

Installation
ExtrabiomesXL is delivered in a single universal download which can be installed on clients and servers alike.

1. Install Minecraft Forge
2. Drag the ExtrabiomesXL download into the mods folder (Don't unarchive it)
3. Enjoy!

Resource Pack Support
A list of resource packs and texture packs which support ExtrabiomesXL can be found on our wiki. We can't guarantee all of these will be up-to-date, however.

Additional Content
ExtrabiomesXL team member gwydion0917 has utilized Custom Stuff 2 to add special red rock versions of furnaces, buttons, pressure plates, etc. It can be found here.

Changelog
The changlog can be found on our Wiki.

Community

• EsperNet IRC: #Extrabiomes
• Blog: http://extrabiomes.com/
• ExtrabiomesXL on Twitter: @ExtrabiomesXL

Localization
ExtrabiomesXL is currently available in English, French, German, Italian, Polish, Portuguese, Russian, Simplified Chinese, Spanish, and Swedish.As ExtrabiomesXL updates with new content, however, we can't guarantee these localizations will remain up-to-date. We'd greatly appreciate any assistance in ensuring all of ExtrabiomesXL's localizations are up-to-date and accurate. A list of the localization files can be found here. Always feel free to add new languages! Our localizations are done by hand, by speakers of the select language for utmost quality, so please no Google Translate. Thank you!

Modpacks
You are free to distribute ExtrabiomesXL in your modpack, so long as it's not being used to make money.Credits

• Original mod by MisterFiber
• Development, design, quality control, and artwork by the ExtrabiomesXL team
• Plenty additional contributions by open source contributors

Support
If you have any problems or questions, please ask in the forum. Be advised, however, that we can never diagnose or fix anything without a complete log file. You should post your complete log (ForgeModLoader-0.log, or ForgeModLoader-client-0.log) on pastebin (or any other similar text sharing service) and then post a link to it here in the forum. The community around this thread likes solving support issues and the most important step you can take is posting your complete log file. Any support requests should be handled publicly where everyone can benefit. Please do not PM the team members with support requests!

Note: Failure to post complete log files using the directions outlined above severely reduces the likelihood that you will achieve a successful outcome to your support your support issue. How to receive support if you do not have a crash report. In the event that Minecraft didn't crash and you did not get a crash report, don't worry. Crash reports are not helpful or wanted. To receive support for your issue, post a complete log by following the above instructions.

FAQ
A list of frequently asked questions is available on our Wiki.

Screenshots

Videos

Signature Banners
Show your support for ExtrabiomesXL with one of our community made banners available from the wiki!