If you're on Gentoo and trying to play minecraft, this guide is for you. This is a modified version from here. However for completeness sake, I'll have the entire guide here too.

First you need to install icedtea, a FOSS JVM. To install it, emerge it

sudo emerge icedtea

That might take a while to emerge. Once its done, set is as the default system JVM

sudo eselect java-vm list; sudo eselect java-vm system

Of course substitute the number for the list entry that says icedtea. If you want to only set this for your user, don't use sudo.

Now download the executable file for minecraft. Its on mojangs site, but this should be a link to it as of this writing

Now extract it to wherever you would like minecraft to live on your system

tar xvf Minecraft.tar.gz; cd minecraft-launcher

Now that you've cd'd into the launcher folder, run the minecraft-lancher. You may run into an error along the lines of

MessageBox(Minecraft Launcher): Couldn't load launcher core from /home/USER/.minecraft/launcher/liblauncher.so: LoadErrorNotPresent

If you poke around you'll find that shared object file exists and lives in the right place, it just seems to be linking against non existant libraries, but that's OK. (On a unrelated note, its very interesting that the launcher is an electron app that also forces itself to live in your home directory. Just thought that was interesting)

So you need to install the correct libraries for minecraft to load, and its looking for libsecret. So we can emerge that

sudo emerge app-crypt/libsecret

On my system it pulled in 3 other dependencies, so your mileage on may vary on how much it pulls in. Now all you have to do is pull in.

After this all you have to do is run the launcher, sign in and it should work right out of the box! Hope this was helpful, and have fun!