$ java -jar Downloads/minecraft.jar
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Exception in thread "Minecraft main thread" java.lang.UnsatisfiedLinkError: /home/desktop/.minecraft/bin/natives/liblwjgl.so: /home/desktop/.minecraft/bin/natives/liblwjgl.so: wrong ELF class: ELFCLASS32 (Possible cause: architecture word width mismatch)
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1928)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1825)
at java.lang.Runtime.load0(Runtime.java:792)
at java.lang.System.load(System.java:1059)
at org.lwjgl.Sys$1.run(Sys.java:69)
at java.security.AccessController.doPrivileged(Native Method)
at org.lwjgl.Sys.doLoadLibrary(Sys.java:65)
at org.lwjgl.Sys.loadLibrary(Sys.java:81)
at org.lwjgl.Sys.<clinit>(Sys.java:98)
at org.lwjgl.opengl.Display.<clinit>(Display.java:132)
at net.minecraft.client.Minecraft.a(SourceFile:187)
at net.minecraft.client.Minecraft.run(SourceFile:644)
at java.lang.Thread.run(Thread.java:722)
https://bugs.gentoo.org/show_bug.cgi?id=391243
solution: add 64 bit natives and fix natives paths, townsgame does it properly.
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Comments

Not fixed.
I said before this is a problem with minecraft only, other java games detect libraries properly.
PLEASE FIX. update your LWJGL or whatever libs that is causing this problem.
In ticket MC-4496 is the solution: