Fixing Minecraft on Ubuntu with OpenJDK

Minecraft! On Ubuntu! It actually runs great, once you actually get it to run, but there were two little things mere mortals can’t be reasonably expected to debug.

Can’t connect to minecraft.net

My Internet connection worked, minecraft.net was up, friends were able to connect just fine, but I couldn’t. Running it from the terminal via java -jar minecraft.jar showed the error message java.security.InvalidAlgorithmParameterException: the trustAnchors parameter must be non-empty.

Basically, Minecraft uses SSL to protect your login, but Java didn’t have the certificates needed to verify. The Minecraft launcher really should give a better error message, but this was really Ubuntu’s fault. You need the ca-certificates-java package installed, but on my Ubuntu install, it was broken. Try doing ls /etc/ssl/certs/java/cacerts. If it comes up missing, then you need copy it from a friend or a different Unix machine. You don’t want to copy security files from strangers…

Black screen

Looking in the terminal showed the error java.lang.UnsatisfiedLinkError: ...: libjawt.so: cannot open shared object file: No such file or directory. There’s no good reason why an OpenJDK install can’t find its own damn libraries, but you can manually set your LD_LIBRARY_PATH variable to contain it.

Try doing locate libjawt.so. You’ll want to set your LD_LIBRARY_PATH to include one of the directories it gives you (just the directory, not included the file). Depending on whether you have OpenJDK 6 or 7, you’ll do something like:

LD_LIBRARY_PATH=/usr/lib/jvm/java-7-openjdk-i386/jre/lib/i386/ java -jar minecraft.jar

Again, check the results of locate versus your OpenJDK version (if you’re not sure, run java -version).

Getting the Sparkfun EL Escudo to work

I’m really disappointed in Sparkfun. I recently purchased the EL Escudo shield for driving EL wire with a microcontroller, and woe be upon anybody who doesn’t do hours and hours of Internet research before plugging the thing in. There were 3 years of questions from poor customers with only a few answers, and the few answers that were there were often contradictory. Here are my conclusions from my Internet research, and the amazing Will Byrd helped me finally get it to work. Long story short, Sparkfun sets you up to fail and hasn’t fixed things in 3 years.


Continue reading Getting the Sparkfun EL Escudo to work

Ubuntu works great with the MSP430 Launchpad

I got my MSP430 TI Launchpad more than a year ago simply because of the price. It was (and still is) $4.30 (with free shipping!) for a development board, two MSP430 microcontrollers, external crystal, and USB cable. Unfortunately, Windows was the only supported OS at launch time with a couple proprietary bundled IDEs. It still is the only officially supported OS, but setting up Ubuntu 11.10 and newer for the msp430 has become trivial:

sudo apt-get install gcc-msp430 gdb-msp430 mspdebug

To test your Launchpad, try compiling “blink” from https://github.com/mrothe/ti-launchpad.

The build process goes something like:

msp430-gcc -Os -mmcu=msp430x2012 -o main.elf main.c
msp430-objcopy -O ihex main.elf main.hex # generate hex file
mspdebug rf2500 "prog main.hex" # download to the launchpad

Do mind your O, o, and 0.