jump to navigation

Java 6 and librxtxSerial.jnilib on Intel Mac OS X August 18, 2009

Posted by Robert Harder in Utility.

[UPDATE: This library works with Mac OS X 10.6 Snow Leopard.]

In order to access a serial port in Java, you need the RXTX libraries compiled for your specific hardware. Java uses the Java Native Interface (JNI) to bridge between your platform-independent application code and the hardware-specific serial port drivers.

If you’ve tried this on an Intel Mac (perhaps to play with a Sun SPOT), you may be disappointed, since software keeps shipping from people that is either PowerPC only or isn’t compiled for 64-bit Intel. You’ve probably seen the UnsatisfiedLinkError message. Here you’ll find a librxtxSerial.jnilib file with support for both 32- and 64-bit PPC and Intel architectures, fitting the bill perfectly for both Java 5 and Java 6 on the Mac.

$ file librxtxSerial.jnilib
librxtxSerial.jnilib: Mach-O universal binary with 4 architectures
librxtxSerial.jnilib (for architecture x86_64):	Mach-O 64-bit bundle x86_64
librxtxSerial.jnilib (for architecture i386):	Mach-O bundle i386
librxtxSerial.jnilib (for architecture ppc7400): Mach-O bundle ppc
librxtxSerial.jnilib (for architecture ppc64):	Mach-O 64-bit bundle ppc64

The Need for the RXTX Library

Java’s “write once, run many” theory of operation works because the Java Virtual Machine (JVM), which must be made for each platform, abstracts away the underlying hardware. As a programmer you can draw circles, label buttons, and even play multimedia without specific knowledge of the host operating system.

A computer’s serial ports can be abstracted away in the same way, but the standard JVM does not provide a mechanism for this. Sun decided (reasonably, though regrettably, I think) that the serial port would not be a required component for a JVM, and so there are no built-in classes for working with serial ports.

Sun experimented, for a period of time, with a Java Communications API that would be a sort of plugin for working with things like serial ports (and parallel ports!), but the project and its javax.comm package died.

Thanks to the team at RXTX.org, we now have a gnu.io package modeled after Sun’s javax.comm package that is maintained and works. Thanks!

Why Doesn’t It Work for You?

If you’re reading this, it might be because you can’t get it to work on your Mac. Probably you have an Intel Mac and are using Java 6 or later which requires a 64-bit Intel processor. Perhaps you’ve seen error messages that say thinks like UnsatisfiedLinkError and so forth.

Software talking to the serial port must communicate with the host operating system, and so the underlying native library must be compiled per-platform. Presumably your librxtxSerial.jnilib file is not compiled for your platform. Here’s how to find out. Open the Terminal, navigate to the folder with a librxtxSerial.jnilib file, and use the file command. You’ll probably see this:

$ cd /Users/rob/SunSPOT/sdk/lib
$ file librxtxSerial.jnilib
librxtxSerial.jnilib: Mach-O universal binary with 2 architectures
librxtxSerial.jnilib (for architecture i386):	Mach-O bundle i386
librxtxSerial.jnilib (for architecture ppc7400): Mach-O bundle ppc

If you’re running Java 5 (which comes in 32- and 64-bit flavors on the Mac) you’re OK, but if you’re running Java 6, which is 64-bit Intel only, it won’t work.

A Library with the Right Architectures

No problem; all you have to do is re-compile RXTX from sources for your platform, right? I wish. I can’t even remember all the contortions I went through before I finally got it compiled.

You’re welcome to follow the various instructions online for compiling it yourself, but it gave me a lot of grief, so I’m placing a copy on this site (if you trust me not to insert nefarious code). I finally had to patch SerialImpl.c and SerialImpl.h (manually) based on the patch instructions here and blog posting here.

At the end of the day, we have a librxtxSerial.jnilib file that has 32- and 64-bit PPC and Intel architectures.

Find all instances of librxtxSerial.jnilib on your Mac and replace them with the one you downloaded from here (or compiled yourself). Try the command locate librxtxSerial.jnilib in the Terminal to find extra copies hidden in various Java applications.


1. Pete - October 12, 2009

THanks man, save me trying out the hours of compiling you went through! I’m wondering, will the .jar from RXTX be the one I need for the jnilib? It looks like it’s working so far.

Robert Harder - October 12, 2009

Yes, the standard .jar file from rxtx should be fine. Happy coding to all. -Rob

2. Patrick - November 1, 2009

Thanks for the post. It’s a really useful info!!

A quick question, do I need to compile 64-bit .dll if I want to use rxtx with JDK6 in Windows environment?

Robert Harder - November 1, 2009

Good question. I suppose if you have 64-bit Windows with a 64-bit Java then you’d need a 64-bit RXTX library. I’m sorry I don’t have one compiled for you. -Rob

3. Peter - November 4, 2009

Robert, I had been banging my head against the wall for a couple of days until now. Thanks you so much for working better than Tylenol.

4. andrew - November 25, 2009

thanks for sharing. btw, java comm. is not dead, but they discontinued support for windows and never supported mac.

5. SP - February 3, 2010

Can you please also post RXTXcomm.jar file?


6. Robert Harder - February 4, 2010

Rather than post stale files, and in keeping with good practices, here’s the link to the download page, if you’re having trouble finding it:



7. Ignacio de Córdoba - February 20, 2010

just to be sure… which of the 3/4 versions available in the qbang download page is the one you used for this compile?
Thanks a lot

8. Robert Harder - February 20, 2010

I don’t remember, but surely I chose the line that reads, “rxtx 2.1-7r2 (stable) rxtx-2.1-7-bins-r2.zip rxtx-2.1-7r2.zip.” -Rob

9. Ignacio de Córdoba - February 21, 2010

Hi again Robert and thanks for your help…
I can only put to work rxtx-2.2pre2 with the built in file (3 architectures including Mach-O 64-bit bundle x86_64). I anyway get a full JVM crash when I am finished and do SerialPort.close().
With rxtx 2.1-7r2 and your jndi file I get a gnu.io.PortInUseException: Unknown Application at gnu.io.CommPortIdentifier.open(CommPortIdentifier.java:354)
Thanks for any directions 🙂

10. Robert Harder - February 23, 2010

Ignacio, I’m sorry that I can’t think of anything really useful to try, but if you have other versions of java on your Mac, you might try running your code with them just to see if the crash is unique to one version or another. -Rob

11. Stephane D. - March 5, 2010

Thank you a lot for your help!! I can finally do my application work on Max OS 10.6 . Your librxtxSerial.jnilib fix my problem.
Have a good day!

12. Christoph - March 25, 2010

@Ignacio: The problem is with the lock file. See http://atelier.tkrworks.net/doc/about-picnomeserial?lang=en how to fix it

13. Art - April 11, 2010

Worked splendidly for me on Snow Leopard, after I created the /var/lock file directory (didn’t work without that change). The RXTX installation page talks about how to create the lock file directory using the fixperm.sh script. That page correctly tells you that you need to modify the path in the script to /var/lock, but the script uses niutil, which apparently isn’t part of Snow Leopard anymore. The instructions Christoph pointed to are better.

14. Joe - May 29, 2010

Thank you so much, its always nice to find someone else with the same problem who has managed a solution.

15. Dave - June 3, 2010

Thanks for making this jnilib available. Works great on my Mac. Now if I could just find a solution for the kernel panics caused by the Silabs CP210x Mac virtual com port driver. Anyone else running into that?

16. Dietmar - September 11, 2010

Thanks Robert for your work.

Now also Mac OS 64bit users can use you vna/J.

Have a nice day ahead

Dietmar, DL2SBA

17. Michael Shimniok - September 15, 2010

THANK YOU for your hard work. I really appreciate the time you saved me in recompiling the rxtx jnilib and making it available to the world.

Am on OS X 10.6, was able to get my serial app launched using your jnilib and then fixed the “gnu.io.PortInUseException: Unknown Application” issue with instructions posted in comments above: http://atelier.tkrworks.net/doc/about-picnomeserial?lang=en


18. WHY - November 22, 2010

Thank you SO much!! My application finally works with your librxtxSerial.jnilib.

however, still there is a problem. My device is connected to a MACBook thorugh a usb-serial adaptor. The application can only run once correctly, if I colse the appliction, start again, it will not able to access the serial port. I have to unplug and plug again the usb-serial port adaptor. Do you think anything wrong?

19. Robert Harder - November 22, 2010

@WHY That happened to me before, and I’m trying to remember how I resolved it. I think what it came down to was that the JVM wasn’t releasing the virtual machine, but I don’t remember how that was happening even after I had closed the Java app. I don’t remember what I did to fix it, or if it just stopped on its own.

20. Seb - January 26, 2011

Thank you very much for this. I was trying to find out why it was not working on my macbook until I realised I was running 64-bit.

21. Bill Dunbar - May 2, 2011

Mr. Harder:

Thanks a bunch for the modified librxtx.Serial.jnilib file. It solved a problem we were having with MorseKOB on the Mac, a program that some of us old (and new) telegraph operators use to communicate in authentic landline Morse code (url below).

Problem was that using the Options to change either the Mode or Port resulted in the browser crashing.

Thanks again!

22. togarha - May 12, 2011


I’m an user of rxtx library, I’m trying to compile the rxtx library for mac osx as you say in your web, but I can’t get the same result as you. I can’t compile for ppc64. If I put only -arch i386, -arch ppc, -arch x86_64 it doesn’t not compile for ppc64, If I try to compile with -arch ppc64 the compilation makes error…

Furthermore, my compilation doesn’t work with x86_64 with java6. Your file works fine, but I want this file without lock files, this is why I want to compile a new file…

I hope you can help me…


23. Robert Harder - May 12, 2011

I’ve been meaning to try to recreate my compilation instructions. Maybe I can get around to that. I don’t remember for sure, but I think I had to compile PPC separately and merge it with the other architectures. I don’t remember if I had to do it on a PPC machine or not, but I’m pretty sure it was pre-Snow Leopard, and I hope I still have the ability to cross compile to PPC.

24. togarha - May 12, 2011

Really I don’t need the ppc compilation, I only need x86_64, but my compilation doesn’t work in x86_64 (making changes you say)

25. Stefan - May 20, 2011

I got an gnu.io.PortInUseException on OS X 10.6.7 (x86_64) Macbook Air and had to run:

sudo mkdir /var/lock
sudo chmod a+wrx /var/lock

in the terminal to get it working…

Thanks for the effort!

26. Duncan - August 7, 2011

Many thanks!
This works with Stefan’s fix on OSX Lion 64-bit Intel.

27. Thomas Kilian - August 28, 2011

Thanks for that. I got a message that the file was not on my Lion system. Indeed there was a symbolic link and a directory with that name in /Library/Java/Extensions. But no real contents. I removed the link and the directory, placed librxtxSerial.jnilib there and my problems were gone.

28. Phil Ershler - September 9, 2011

I have downloaded your modified librxtxSerial.jnilib on my 10.6.8 Snow Leopard machine. But I still get the following problem.

CommPortIdentifier:static initialization()
WARNING: RXTX Version mismatch
Jar version = RXTX-2.2pre1
native lib Version = RXTX-2.1-7
Exception in thread “main” java.lang.UnsatisfiedLinkError: no rxtxSerial in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1758)
at java.lang.Runtime.loadLibrary0(Runtime.java:823)
at java.lang.System.loadLibrary(System.java:1045)
at hts.HTS_UI.(HTS_UI.java:689)
Experimental: JNI_OnLoad called.

Please bear in mind that my Java skills are quite primitive.


29. Robert Harder - September 9, 2011

@Phil Try running the command “file $(which java)” (no quotes) and see what architectures you’re shown. There should be overlap with librxtxSerial.jnilib. It’s possible that Java is loading a pre-existing librxtxSerial.jnilib file w/o the right architectures. Look for other librxtxSerial.jnilib files and replace them perhaps.

30. Jim Hannon - September 23, 2011

Thanks so much for the library file. Works great for me. I appreciate it.

31. Rose G - November 8, 2011

Hi I am using Mac OSX Lion 10.7 and receiving the following:
java.lang.UnsatisfiedLinkError: no rxtxSerial in java.library.path thrown while loading gnu.io.RXTXCommDriver
Exception in thread “main” java.lang.UnsatisfiedLinkError: no rxtxSerial in java.library.path

I’ve tried so many solutions such as changing location of the rxtxSerial from extension to the actual src file of my java project as well as using Java 5..

Any Suggestions?

Robert Harder - November 8, 2011

I haven’t tried it since going to Lion, nor do I have a way to test it out right now. Sorry. -Rob

32. Tom - November 30, 2011

Works great on Lion. Thanks a lot!

33. Suhas - January 31, 2012

If you get Portinuse exception, then please do following


As a nice anonymous user comments, these are the steps to go:
Open ‘Terminal’ from Applications->Utilities
Enter the commands:
sudo mkdir /var/lock (hit enter end type your password)
sudo chmod 777 /var/lock (hit enter again)

34. Ankur Oberoi - March 5, 2012

@Rose G, the instructions from Suhas fixed that problem for me. Thank you so much!

35. nandish - April 9, 2012

Thanks it worked for me

36. Diego Beltrán - August 6, 2012

Very impressive Work, thank you so much.

37. Comunicação Serial (RXTX) com Java e Arduino no Mac OS X | Blog do Renato Peterman - September 18, 2012

[…] segundo seu site, suporta tanto as versões 32 quanto 64 bits, Intel ou PowerPC. Na página tem explicação mais detalhada. Pra fazer o download direto clique […]

38. Girts - September 26, 2012

Thank you very much, you saved a lot of time for me! 🙂

39. Marcel Fiechter - November 8, 2012

Thanks a lot for your great work! It helped me a lot. I tested everything the last maybe even more then 7 days. This knowhow i would like to share, just in case somebody else has the same problems. The Version from Robert Harder is 2.1-7. With this Version you have to build a var/lock directory with the right permissions. The problem is that from Mac OS 10.5 this directory isn’t installed. The problem is also that the error message is portinuse-exception. Even the port is not in use. Just the directory is missing. You can loose a lot of time to find the solution this way. RXTXcomm.jar Version 2.2 doesn’t need this var/lock-directory. I tested really almost all possibilities from Cloudhopper to jlog and so far. There are always some disadvantages. Cloudhopper for example doesn’t support Mac. If you do it like I write her, you can save a lot of time. It works for all OS. Go to http://rxtx.qbang.org/wiki/index.php/Download. Download rxtx-2.2pre2-bins.zip. Take RXTXcomm.jar and put it to Java/lib/ext on Windows or Java/Extensions on Mac. For Windows and Linux take the 32 or 64 Bit version of rxtxserial.dll or librxtxserial.so. For Mac OS 10.5 and lower take librxtxserial.jnilib. In Windows put rxtxserial.dll to Java/bin/. On Mac put it to Library/Java/Extensions. There is no librxtxserial,jnilib for 64-bit Mac. OS 10.6 and higher are always 64-bit. The right file you find here: http://code.google.com/p/create-lab-commons/source/browse/trunk/java/lib/rxtx/ Download librxtxSerial64.jnilib. RXTXcomm.jar won’t find librxtxSerial64. You have to rename it to librxtxSerial.jnilib. Put it to Library/Java/Extensions. Like this everything works without creating a var/lock-directory and troubleshooting around the wrong Error Message portinuse-Exception. Anyway it’s better to have Version 2.2 instead of 2.1-7 if there are not any other issues. I didn’t find any so far.

2 hints at the end. On Mac with Version 2.1-7 and 2.2 the program crashed at serialPort.Close;. It took me a hell of time until i found out that there must be a serialPort.removeEventListener(); before serialPort.Close; even I didn’t open AddEventListener. This must be a bug. Just put serialPort.removeEventListener(); and everything works fine.

The second hint: I use usb to serial adapter to open a cashdrawer. The first time when i was writing out the Esc-String it was working. But then nothing was writing out any more. But the program finished successfully. Without any error. Very strange. I found out when i write out twice or more times outputStream.write(messageString.getBytes()); then everything worked fine. It was doing the first write and also the second. But when i wrote just one time outputStream.write(messageString.getBytes()); it was just working the first time. Then i could klick a 100 times it didnt’t work any more. I do it now like this:
var justwriteanything = “rrrr”;
outputStream.write( justwriteanything.getBytes());

this way it works always. Strange but true.

40. rjlzaitz - November 17, 2012

Thank You! I’ve been losing my mind over this all day. Trying to open a serial connection via bluetooth between my Arduino and Processing. This fixed it.

41. Jonathan - November 26, 2012

Thank you so much for posting this!

On my other development machine, I forced the compiler into 32-bit mode and on my second machine, I’m using your file.


42. ajayp - December 11, 2012

just a heads-up that this works on mountain lion 10.8.2 as well. thanks sir, this is super duper extra appreciated.

43. George - December 11, 2012

I can’t seem to get it to install correctly in OSX 10.7.5 machine. I put both files: RXTXcomm.jar and librxtxSerial.jnilib (originally downloaded as librxtxSerial64.jnilib)
in /Library/Java/Extensions
I am using Eclipse Indigo r2, and have added RXTXcomm.jar into the build path of my project. I am getting error messages on the “import gnu.io.xxxxx” lines.
Any suggestions?

44. George - December 11, 2012

I just saw the error message in Eclipse telling me that the file Archive for required library: /Library/….. /RXTXcomm.jar in project xxx “cannot be read or is not a valid zip file”. I have an extension installed that allows me to look into the contents of the .jar’s and the contents look fine. In fact all my projects had the error and I had to remove the entire JRE system library from each project and add it back in again. I assume this is some kind of Eclipse issue and not Java per se.

45. George - December 12, 2012

Problem solved. I had a Processing plugin installed on Eclipse and it had a 32 bit version of the librxtxSerial.jnilib. I should have read this post more carefully, especially this quote:

“Find all instances of librxtxSerial.jnilib on your Mac and replace them with the one you downloaded from here ”

and not jumped around to the latest comments. Lesson learned.

46. Telnet to a BBS, using a terminal program within an emulator | Break Into Chat - December 13, 2012

[…] to run, and my Mac Pro runs in 64-bit mode, which introduces a wrinkle. However, by following instructions from Marcel Fiechter I got RXTXComm […]

47. videos von youtube downloaden - February 15, 2013

Tomb Raider, Mega Moolah, Mermaid’s Millions, and Blackjack are some of the new Android game apps that have been released from Microgaming’s partner,
Spin 3. You will eventually run into the Download Location menu with two options: Wii System Menu and
SD Card. A Twitter app for Zune has been created and is now available for download
through Microsoft’s Marketplace.

48. Jake - March 9, 2013

Thanks so much – worked a treat. Been trying to find a solution to this for ages.

49. Installing RXTX on Mac OS Mountain Lion | Brian's Blog - - March 9, 2013

[…] to Robert Harder’s blog and download his version of the librxtxSerial.jnilib file. Direct link here. Just want to say […]

50. raspberry ketones 100 mg - June 26, 2013

Heya! I just wanted to ask if you ever have any problems with hackers?
My last blog (wordpress) was hacked and I ended up losing a few months of hard work due to
no data backup. Do you have any methods to stop

51. sleeping tablets - July 14, 2013

Oh my goodness! Incredible article dude! Many thanks, However I am experiencing issues with your RSS.
I don’t understand the reason why I cannot join it. Is there anyone else having the same RSS problems? Anyone that knows the answer can you kindly respond? Thanx!!

52. Doug Squires - December 26, 2013

Holy schmoly. Thanks for the lib. I’m working on a silly hobby project and did not want to spend any more time trying to get this stupid thing to build – including finding jdk headers, etc. wowza.

53. Portugal removals - May 5, 2014

You will have access to a helpful message board, learn the latest information on legal issues, and attend
an annual convention if you’d like. The most cost effective option to
move your possessions is nearly always by sea especially if you’ve got several years worth of belongings.

‘ You must check in the internet to find out a company which will serve you when you will be planning to move somewhere abroad.
The last day the Uchidas spent in their Berkeley home before they
were shipped to Tanforan is one such example. They offer a broad range of parallel services that
are designed to further take the pressure off during a move.

54. buy baby bikini onesie - October 8, 2014

buy baby bikini onesie

Think Harder » Java 6 and librxtxSerial.jnilib on Intel Mac OS X

55. corvalgroup.com - October 10, 2014


Think Harder » Java 6 and librxtxSerial.jnilib on Intel Mac OS X

56. zenonia5hackcheattool.wordpress.com - October 10, 2014

Hi, its good paragraph concerning media print,
we all know media is a fantastic source of facts.

57. Talking to Your Arduino with Java | ellipsistechnology - April 24, 2015

[…] by downloading a more complete and compatible version of the native side of the RXTX library from here. Use this to replace the .jnilib file in /path-to-lib/rxtx-2.1-7-bins-r2/Mac_OS_X. Big thanks to […]

58. David - May 4, 2015

I just stumbled upon new serial port library which seems promising and save my time to build for different operating systems https://github.com/RishiGupta12/serial-communication-manager

59. Java RXTX Library doesn't load native library - BlogoSfera - July 3, 2015

[…] RXTX: 2.1-7r2 – modified version for intel mac running 64 bit java, which can be found here. IDE: NetBeans […]

60. Java RXTX Library doesn't load native library - codeengine - July 22, 2015

[…] RXTX: 2.1-7r2 – modified version for intel mac running 64 bit java, which can be found here. IDE: NetBeans […]

61. RXTX for Java + Arduino Communication – Afterday - February 21, 2016

[…] -RXTX Libraries : Can be downloaded at: RXTX Libraries (Warning – If you need the 64 bit libraries, you will have to source them elsewhere. If you need the more rare mac os x 64 bit JNI library, you can get it here: RXTX 64 bit Library) […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: