Monday, October 28, 2013

RXTX on Mac with Oracle Java 7

I've been using RXTX on the mac for quite some time with the -d32 vm argument. This was necessary with 64-bit Java since the native libraries for RXTX are only compiled for 32-bit mode. Without -d32, you'd get the following error:

java.lang.UnsatisfiedLinkError: librxtxSerial.jnilib: no suitable image found

Apple had always bundled Java with OS X, but about 3 years ago they announced they would no longer do so. Now, to get Java 7 for the mac you need to get it from Oracle. Recently I tried running one of my RXTX apps with Oracle's Java 7 and I got the following error:

Error: This Java instance does not support a 32-bit JVM.

Please install the desired version.

It seems that Oracle no longer supports the -d32 vm argument. You can still run the Apple version of Java 6. The Apple bundled Java versions can be found in


For example:

$ /System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home/bin/java -d32 -version
java version "1.6.0_37"
Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909)
Java HotSpot(TM) Client VM (build 20.12-b01-434, mixed mode)

So to run Oracle Java 7 we need a 64-bit version of RXTX. A few searches led me to Arduino article that mentions Robert Harder's blog post In this post Robert describes how he compiled RXTX for 64-bit Java (apparently not a trivial task). After downloading his librxtxSerial.jnilib it worked, the first time; the second time I got an exception:

“ Unknown Application”

This was super annoying since I didn't have any other Java processes running that had the port open. I read through the comments and found a solution:

sudo mkdir /var/lock

sudo chmod a+wrx /var/lock

Apparently RXTX needs this directory to manage locks. This was also mentioned on the Arduino article but I missed it the first time. It seems that the Arduino IDE must rely on Java 6 since the RXTX library that comes with the IDE is 32-bit. At some point I imagine (Java 8 perhaps), we'll see more interest in 64-bit RXTX. Please leave a comment if you have any insight on this problem and/or alternative solutions.


  1. Hey Andrew, I wonder if there are any news about a 64-bit version of the RXTX library ans I am using it in a university project. It is getting more and more difficult to get the xbee-api for Java running and I wonder what the future will look like when there is no 32-Java support anymore.

  2. It seems projects are migrating from RXTX to JSSC. The latest Arduino release now uses JSSC