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NOTE: this method is out of date (but correct for 1.6). On 1.7 and higher just drop Optifine in the mods folder after installing Forge. No changes to the jar are needed, other than the changes Forge makes when installing.

Find your .minecraft folder

Before you begin you must find your .minecraft folder. This folder will not exist if you have not run the minecraft launcher at least once. This tutorial will work from within this folder.

OS Path
Linux ~/.minecraft
Windows %appdata%\.minecraft
Mac OS X ~/Library/Application Support/minecraft

In many Linux file managers dot files (files and folders prefixed with a period ".") will be hidden. In Nautilus press ctrl+h to toggle the display of dot files.

Exit from Minecraft and the Minecraft launcher

Exit both Minecraft and the Minecraft launcher.

Install Forge

Install Forge according to the official instructions on http://www.minecraftforge.net/wiki/Installation/Universal, summarized here:

  • download the current or recommended installer version from http://files.minecraftforge.net/
  • double-click on the downloaded jar file, or run it from a command line like this:
java -jar minecraftforge-installer-1.6.2-9.10.0.804.jar

(replacing the filename as necessary).

If you only need the smaller Forge Mod Loader (FML), you can download its installer from http://files.minecraftforge.net/fml/ and use that instead. Forge already includes FML.

Download OptiFine

Download the current OptiFine version from <http://optifine.net/downloads.php>.

Rename the jar file so it starts with "optifine-" (with a hyphen/minus at the end) instead of "OptiFine_" (with an underscore at the end), like "optifine-1.6.2_HD_U_B4.jar".

Create folders in your Minecraft folder like this:

Minecraft folder 
    \- libraries
        \- net
            \- optifine
               \- optifine
                  \- 1.6.2_HD_U_B4

where the last folder name should be the current version number of OptiFine. Put the OptiFine jar file in that folder.

Modify the version JSON

Find the Forge version you'll be using in your Minecraft folder:

Minecraft folder 
    \- versions
        \- 1.6.2-Forge9.10.0.804

In that folder, there is a .json file. Edit that file with a text editor.

Most of that file is a list of libraries:

       "libraries": [
               {
                       "url": "http://files.minecraftforge.net/maven/"
                       "name": "net.minecraftforge:minecraftforge:9.10.0.804"
               },
               {
                       "serverreq": true,
                       "name": "net.minecraft:launchwrapper:1.3"
               },
...
               {
                       "extract": {
                               "exclude": [
                                       "META-INF/"
                               ]
                       },
                       "name": "net.java.jinput:jinput-platform:2.0.5",
                       "natives": {
                               "windows": "natives-windows",
                               "osx": "natives-osx",
                               "linux": "natives-linux"
                       }
               }
       ],
       "mainClass": "net.minecraft.launchwrapper.Launch",
       "minimumLauncherVersion": 4,

At the end of the list of libraries, just before the "]" that ends the list, add a comma after the "}", then fill in an entry for OptiFine that looks like this:

                       "natives": {
                               "windows": "natives-windows",
                               "osx": "natives-osx",
                               "linux": "natives-linux"
                       }
               },
               {
                       "name": "net.optifine:optifine:1.6.2_HD_U_B4",
                       "url": "file:///nonexistent"
               }
       ],
       "mainClass": "net.minecraft.launchwrapper.Launch",
       "minimumLauncherVersion": 4,

Be careful with the positioning of {, } and commas - it does matter!

If you're using FML, the version will look like 1.6.2-FML6.2.29.717 rather than 1.6.2-Forge9.10.0.804. Similar steps apply.

Configuring fml.ignorePatchDiscrepancies=true

Forge is expecting to see an unmodified Minecraft, but we've just modified the version to include OptiFine instead. By default, Forge will refuse to run on a modified Minecraft; now we need to tell it not to worry.

Run the Minecraft launcher. In the bottom left corner, select the Forge profile. Click on "Edit Profile".

File:Fml.ignoreDiscrepancies-step1.png

In the profile details, there's an input box for "Java Arguments", with a checkbox next to it. Check the checkbox, and put this in (If there is anything other than plank space in the box, make sure to put a space in front of it. :)

-Dfml.ignorePatchDiscrepancies=true

File:Fml.ignoreDiscrepancies-step2.png

Save the profile, and play Minecraft. If all goes well, after the Mojang logo has disappeared, the bottom left corner of the Minecraft window will indicate that you're running Forge and OptiFine:

File:Fml.ignoreDiscrepancies-done.png

If you're using FML, select the FML profile instead of Forge. The rest of the steps are the same.

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