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java-linux@java.blackdown.org FAQ by Stephen Wynne September 12, 1998 This document attempts to answer the most commonly-asked questions on the java-linux@java.blackdown.org mailing list. Its focus is the Blackdown JDK. More information on running Java on Linux is available at http://www.blackdown.org/java-linux.html. ______________________________________________________________________ Table of Contents: 1. Introduction to the Blackdown JDK and Mailing List User Guide 1.1. What is the Blackdown JDK? 1.2. Suggestions for List Participants 1.3. How can I get subscribed? Unsubscribed? 1.4. Where Can I Find Archived Postings from this List? 2. Could You Give Me An Overview of Running Java on Linux? 2.1. What is the Currently-supported Version of the Blackdown JDK? 2.2. What System Configuration do I Need to Run the JDK? 2.3. OK, Which Version of the JDK Should I Download? 2.3.1. JDK 1.02 2.3.2. JDK 1.1 2.4. What Are These Files? 2.5. What Other JDK Ports are Available for Linux? 2.6. There's a pure Java Package I Want to Run. Can I? 2.7. When is the JDK 1.2 Going to be Released for Linux? 2.8. Can I Take a Look at the JDK 1.2 Now Anyway? 2.9. Is Javasoft Going to Support Java on Linux? 2.10. What are Green Threads? 2.11. Is There a Native Threads Port of the Blackdown JDK? 2.12. Does Javasoft's Activator JVM work on Linux with Netscape? 2.13. Is there a JIT (Just in Time Compiler) for the Blackdown JDK? 2.14. What Other Java Resources are Available at Blackdown? 2.15. Other Sources of Information about Java on Linux 3. Blackdown JDK Installation Questions 3.1. Where to obtain JDK 1.02 and 1.1? 3.2. How Do I Install the JDK? 4. Troubleshooting the Blackdown JDK on Linux 4.1. Typical Questions to Ask Yourself When Debugging Problems 4.2. Where Can I Report Bugs? 4.2.1. What Should I Report? 4.3. Are There Any Debugging Techniques I Can Try Myself? 4.4. That Didn't Help. What Else Can I Do? 5. Details on Running The Blackdown JDK 5.1. I'm on <your favorite Linux distribution here> What Do I Need? 5.1.1. The glibc versus libc5 Problem 5.1.2. RedHat Installation Tips 5.1.2.1. RedHat RPM Availability 5.1.2.2. RedHat/RPM Environment Variable Issues 5.1.3. Debian 5.1.4. Slackware 5.1.5. Other Linux Distributions 5.2. Is There Anything Different About Native Interfaces on Linux? 5.2.1. Compiling Library Code for JNI 5.3. Is There a Problem with Green Threads and the JVM Invocation API? 5.3.1. Green Threads and Wrapped System Services 5.3.2. Hacking Around the System Service Wrappers 5.4. Kaffe and the Blackdown JDK 1.1 are Installed. Neither Work! 5.5. I Have the Blackdown JDK 1.1.x and RMI is Giving Me Fits! 5.6. Help, I've Upgraded to ld.so-1.9.9 and Now the JDK Coredumps! 5.7. What's Wrong with Thread Priorities and the Console? 5.8. Help, Java Said it Ran out of Memory! 5.9. How Do I Add Swap Space? 5.10. Can I Display and Input Kanji with the Blackdown JDK? 5.10.1. Library Issues 5.10.1.1. Libc5 Systems 5.10.1.2. Libc6 (glibc) Systems 5.10.2. Entering Two Byte Kanji with XIM 6. Questions about Non-i386 Blackdown JDK Ports 6.1. What's the Status of the SPARC Port? 6.2. Is there an Alpha Port? 6.3. Is there a PowerPC Port? 7. General Questions about Java 7.1. Where Can I Learn More about Java? 8. General Questions about Linux 8.1. Where Can I Find Linux FAQs, Mailing Lists, and Documentation? 8.2. What is glibc, and Why Does it Matter? 9. Compiling the Blackdown JDK from Source 9.1. Can I Build Java Myself? 9.2. Could You Give Me a Pointer to Sun's Licensing Agreement? 9.3. How do I Build the JDK Now that I Have the Source? 9.4. What about Motif? Don't I Need That? 9.5. When I Build and Install, I Get Unsatisfied Link Errors at Runtime! 9.6. Can I Try Builds of the Latest JDK Port in Development? 10. About the People Behind the Blackdown JDK 10.1. Who Ported the Blackdown JDK? 10.2. Who is Steve Byrne? 10.3. Who is Karl Asha? 11. Information on the Java-Linux FAQ Itself 11.1. Who Maintains the FAQ? 11.2. Where Can I Get a Copy of the FAQ? 11.3. Please Help the FAQ Maintainer! 11.4. Are there Any Plans for Automating the FAQ? 11.5. Caveat Emptor 11.6. Terms of Use 11.7. Acknowledgements ______________________________________________________________________ $Id: FAQ-java-linux.sgml,v 1.106 1998/09/12 20:24:00 stevemw Exp stevemw $ 1. Introduction to the Blackdown JDK and Mailing List User Guide 1.1. What is the Blackdown JDK? The Blackdown JDK is one of the ports of Sun's Java Developer's Toolkit to Linux. The JDK includes the basic tools needed for developing and running Java applications, including (among other things) the following: o A Java Virtual Machine, or JVM. The virtual machine interprets and executes Java byte codes (a more condensed, intermediate form for Java instructions) inside a software-only machine. In other words, the JVM emulates a hardware platform, including registers, program counter, and so forth. o A Java compiler, which takes a text file containing Java syntax and transforms it into Java byte codes. o An appletviewer for executing Java applet code. o A Java debugger. o Example Java programs. o The Java 1.1 class library, including platform-independent library source. o A tool for creating and managing Java security keys. o A remote method stub and skeleton generator. o A registry server for remote method invocations. o C and C++ headers for extending the JVM with interfaces to native code. o Native libraries for the platform-dependent portions of the JVM, including AWT layer above Motif and X11. o Native libraries for embedding a JVM in other native applications. There are static and dynamic versions of the core Java binaries, as well as versions compiled with and without debugging symbols. Documentation for the JDK APIs is available separately from Javasoft at http://www.javasoft.com/docs/. For information on the Blackdown JDK porting project itself, including who the major contributors have been, please see section ``Who Ported the Blackdown JDK?'' . 1.2. Suggestions for List Participants o Please read http://www.place.org/~stevemw/java/FAQ/README.linux (also found in the Blackdown JDK distribution). o Choose a descriptive Subject: line for your mail. o When reporting problems, please follow the guidelines in section ``What Should I Report?''. o Posts with lines wrapped at 75-80 characters are easier to read! o Spamming the list or using members' E-mail addresses for commercial purposes is forbidden. o Some list users may ignore messages created in HTML or that include proprietary attachments. o Do not followup improper postings to the entire list; copy only the sender and karl@blackdown.org, the list administrator. o Please avoid inflammatory language. 1.3. How can I get subscribed? Unsubscribed? Please don't send E-mail directly to the list requesting these status changes! Visit http://www.blackdown.org/java-linux.html and follow the links to instructions or use the links provided in the next paragraph. The following URL would work in Netscape Mail to subscribe you: java- linux-request@java.blackdown.org?subject=subscribe And this should unsubscribe: java-linux- request@java.blackdown.org?subject=unsubscribe 1.4. Where Can I Find Archived Postings from this List? Karl Asha has arranged for the list to be archived here: http://www.mail-archive.com/java-linux@java.blackdown.org/. 2. Could You Give Me An Overview of Running Java on Linux? Running Java on Linux is about what you'd expect. You should be able to run most "pure Java" applications on the Linux JDK or JRE. It does take a little longer to get the latest JDK on a target that Javasoft doesn't officially support. Also, the JVM currently only uses green threads. See section ``What are Green Threads?''. 2.1. What is the Currently-supported Version of the Blackdown JDK? At the time of this writing, the latest supported Blackdown JDK version is 1.1.6v2. Please see section ``Where to obtain JDK 1.02 and 1.1?'' for places to download. To determine your version, use this command: ______________________________________________________________________ $ java -version ______________________________________________________________________ 2.2. What System Configuration do I Need to Run the JDK? This is only a basic summary. The Alpha, SPARC, and PPC platforms may have different requirements, for example. 1. A supported platform running regular, 32-bit Linux is required. See section ``OK, Which Version of the JDK Should I Download?'' for details. 2. You need at a minimum, 20MB of free virtual memory to run the JDK. See section ``How Do I Add Swap Space?'' for more information. 3. Including HTML documentation and i18n.jar, JDK 1.1.6 i386 glibc version takes 34MB of free space. You can make it smaller by removing these and the demos. 4. To run AWT, you'll need X11 up and running. 5. Sound cards are supported but not required. 2.3. OK, Which Version of the JDK Should I Download? This section closely matches the organization of the Blackdown distribution mirror hierarchy. This part of the FAQ is rather thin on details at the moment, but it should help you to see which archive to retrieve. You may also be interested in reading section ``What System Configuration do I Need to Run the JDK?'' above. After reading this, if you're still wondering which individual archive to download, please see ``What Are These Files?'' below. 2.3.1. JDK 1.02 The Blackdown version of the JDK is only supported on Intel. If you know of other Linux platforms to which the JDK has been ported, please tell the FAQ maintainer. Look for the mirror closest to you by following instructions in section ``Where to obtain JDK 1.02 and 1.1?''. 2.3.2. JDK 1.1 o Alpha ................................ alpha/ o Intel x86 ................................ i386/ o SPARC ................................ sparclinux/ o PowerPC ................................ mklinux/ o Patches to Javasoft Source, etc... ................................ common/ You may wish to read section ``What is glibc, and Why Does it Matter?'' to help you understand which Intel JDK to download. To just run the JDK, you don't need anything out of common/. Those diff(1) files are for people who want to request free access to the SPARC/x86 Solaris and i386 Win32 sources from Sun and help with the port. See section ``Compiling the Blackdown JDK from Source'' for more information. 2.4. What Are These Files? By now, many readers are still wondering what each archive in the mirror directories is. Below is a representation of what your favorite web browser would have displayed if you were visiting a Blackdown JDK mirror recently. ______________________________________________________________________ Current directory is /pub/java/JDK-1.1.6/i386/glibc/v2 Up to higher level directory i18n1.1.6-v2-glibc.tar.gz 2485 Kb Fri Jun 19 21:56:00 1998... jdk1.1.6-v2-glibc.tar.gz 11734 Kb Fri Jun 19 21:56:00 1998... jre1.1.6-v2-glibc.tar.gz 6089 Kb Fri Jun 19 21:56:00 1998... rt1.1.6-v2-glibc.tar.gz 3603 Kb Fri Jun 19 21:56:00 1998... ______________________________________________________________________ At this point, you've already decided that your system is based on glibc (perhaps by reading ``What is glibc, and Why Does it Matter?''). Now you'd like to know what these four files do for you, and which ones you should download. 1. jdk. The JDK contains everything you need to run Java, compile Java, and debug java. It doesn't contain the international character converters (see i18n). 2. jre. The JRE is the Java runtime environment, including the international character converters. 3. rt. The Java RT is the minimal configuration you can have to run Java. It doesn't contain any internationalization support. 4. i18n. This contains font mappings and a JAR file containing the international character converters, and really doesn't need to be split off by library type, but is anyway. 2.5. What Other JDK Ports are Available for Linux? Please see section ``Questions about Non-i386 Blackdown JDK Ports'' for more information. http://www.blackdown.org/java-linux/ports.html. 2.6. There's a pure Java Package I Want to Run. Can I? Most likely. For example, I've tested Javasoft's JFC SwingSet (see http://java.sun.com/products/jfc/) with a static Motif build and a Lesstif build with good results. This typically involves downloading the package and untarring or unzipping it. Sometimes the vendor won't provide an installation procedure that works well on Linux, and so you have to adjust a script or do it by hand. 2.7. When is the JDK 1.2 Going to be Released for Linux? According to Steve Byrne on Monday, May 26th 1998: JavaSoft is trying very hard to get a license set up with an external person to coordinate the 1.2 Linux porting effort. The plan is not to have to wait until 1.2 ships, but to get things underway much sooner (1.2 is huge, and involves lots more machine specific components, and will take a while to port). 2.8. Can I Take a Look at the JDK 1.2 Now Anyway? Yes, just run unzip on the Solaris shell script archive; it'll unpack it for you. You can then unpack the src.zip archive. Also, you can already get the documentation from Javasoft from http://www.javasoft.com/docs/index.html. 2.9. Is Javasoft Going to Support Java on Linux? We don't know yet. At the time of this writing, bug 4097810 was at the top of the JDC Bug Parade. You can read about it at: http://developer.java.sun.com/developer/bugParade/bugs/4097810.html. There are a number of complex issues involved with this request, including the wide variety of Linux distributions, target architectures (beyond Intel where Javasoft already supports Solaris x86), the huge number of announced APIs with required native support, and so forth. 2.10. What are Green Threads? Green threads use some magic with jmp_bufs, stack pointers, the program counter, and some other hocus pocus to schedule different instruction streams. This gives the practical effect of multi- threading with some caveats about signals and how they're handled across longjmp()s. See the discussion of native threads in section ``Is There a Native Threads Port of the Blackdown JDK?''. Jon Waette <hplus@zilker.net>, has a brief synopsis of green threads at http://www.zilker.net/~hplus/jvm.html. He states: Sun's Java VM as running on Solaris [without the native threads package] used a user-level thread package named Green Threads. This is strictly a collaborative threading package; the JVM is one system process and only executes one Java code stream at a time. This is convenient for implementors, because special operations that required nobody else to touch sensitive data are intrinsically protected. As long as you don't relinquish the CPU (and block signals) you're in no danger. If you do a [System.in.readLine()], the JVM will sit in the blocking input call until input is available; nothing else will happen in your program. If anyone has a clearer explanation of this than the FAQ maintainer's, please contribute. 2.11. Is There a Native Threads Port of the Blackdown JDK? Not at this time. Karl Asha has this to say: Native threading in the jdk is partially a dream. There's a lot of problems with linux's pthreads implementation for starters, and second it'll take a reasonable effort to get them into the jdk itself. 2.12. Does Javasoft's Activator JVM work on Linux with Netscape? Take a look at http://www.blackdown.org/activator/. 2.13. Is there a JIT (Just in Time Compiler) for the Blackdown JDK? There are several. Please take a look at http://www.blackdown.org/java-linux/javatools.html for pointers. Alexander Davydenko <alex@Javad.Ru> posted an updated configure script to install TYA that this author hasn't tested. You can read his post at http://www.mail-archive.com/java- linux@java.blackdown.org/msg00126.html 2.14. What Other Java Resources are Available at Blackdown? Karl Asha's Blackdown server, http://www.blackdown.org/java- linux.html, has a number of resources. Among other things, Karl provides the following pointers: o Recent news about running Java on Linux: http://www.blackdown.org/java-linux/info.html o Javasoft-supplied products: http://www.blackdown.org/java- linux/products.html o The Blackdown port of the Java Activator Plugin for Netscape: http://www.blackdown.org/activator/ o Java Tools: http://www.blackdown.org/java-linux/javatools.html o Information about Third-party Java products running on Linux: http://www.blackdown.org/java-linux/otherproducts.html 2.15. Other Sources of Information about Java on Linux o Luiz Otavio Lautenschlaeger Zorzella has a general "Java on Linux FAQ" at http://nr.conexware.com/~zorzella/wine/FAQ2.htm o Paul Cho has an up-to-date Linux/Java page worth reading often: http://www.w3com.com/paulcho/javalinux/ o Professor Sergey Nitikin's Linux/Java News: http://www.public.asu.edu/~nikitin/JavaOnline/ 3. Blackdown JDK Installation Questions 3.1. Where to obtain JDK 1.02 and 1.1? Please visit http://www.blackdown.org/java-linux/mirrors.html and select the site nearest you. Both Randy Chapman's JDK 1.02 and Steve Byrne's JDK 1.1.x are found on participating mirror sites. Check section ``What is the Currently-supported Version of the Blackdown JDK?'' for the currently supported version the Blackdown JDK. 3.2. How Do I Install the JDK? 1. Download the tar(1) archive for your platform as directed by the mirror list mentioned in section ``Where to obtain JDK 1.02 and 1.1?''. 2. Move to an appropriate directory and for example, unpack the tar(1) archive as follows: ___________________________________________________________________ $ cd /usr/local $ tar zxvf /tmp/jdk1.1.6.tar.gz ___________________________________________________________________ 3. Make sure your DISPLAY environment variable is set, put the resulting directory into your execution path, and try something: ___________________________________________________________________ $ export DISPLAY=:0 $ export PATH=/usr/local/jdk1.1.6/bin:$PATH $ appletviewer \ /usr/local/jdk1.1.6/demo/awt-1.1/lightweight/OpenlookButtons/example.html ___________________________________________________________________ Note that the above examples assumed you were using the Bash shell, such as /bin/bash. Also note that if you already have a CLASSPATH set, you'll probably want to append .:/usr/local/jdk1.1.6/lib/classes.zip: to that environment variable. This ensures that you have the current working-directory in your class search path, and makes things much easier for you as you test your code. Of course you may want to add these environment commands to your shell's startup script, such as $HOME/.bashrc. Some people may wish to set JAVA_HOME themselves. That way, you can change all commands following setting that to use it instead, such as ______________________________________________________________________ $ export JAVA_HOME=/usr/local/jdk1.1.6 $ export PATH=$JAVA_HOME/bin:$PATH $ export CLASSPATH=.:$JAVA_HOME/lib/classes.zip ______________________________________________________________________ 4. Troubleshooting the Blackdown JDK on Linux 4.1. Typical Questions to Ask Yourself When Debugging Problems o Does your system hardware and software satisfy the minimum requirements? See section ``What System Configuration do I Need to Run the JDK?''. o Are you running the current version? You can find that information in section ``What is the Currently-supported Version of the Blackdown JDK?''. o Have you checked to see if your libc, glibc, and X11 libraries could be the problem? See section ``Details on Running The Blackdown JDK''. If you learn something we can add to there, please post them! o Environment Variables. Here are the top candidates for problems: o CLASSPATH Should either be unset or start with .:$JAVA_HOME/lib/classes.zip. o PATH Should include $JAVA_HOME/bin -- ahead of /usr/bin where Kaffe often lives, please! o JAVA_HOME This should be set to your top-level JDK directory. o JDK_HOME Although the JDK doesn't need this, it ought to be set to your top- level JDK directory (if at all). HotJava uses this environment variable, as do other packages other than the JDK. o Are all the required X11 fonts installed? This is a subtle area of concern. People have experienced crashes from not having 75dpi fonts installed. o Are your font and localization properties correct? Another area that is difficult to troubleshoot. I hope to add more information here soon! 4.2. Where Can I Report Bugs? Karl Asha has setup a Jitterbug problem-report form at http://www.blackdown.org/cgi-bin/jdk. Please report problems by filling this in as best you can. There are some guidelines for this in section ``What Should I Report?''. Before submitting a bug, you may be able to help by visiting Javasoft's Bug Parade at http://developer.java.sun.com/developer/bugParade/bugs/ and checking for related problems. If you mention a bug from a JDC bug ID in your problem report, it can help Blackdown JDK developers. At this time, you will have to join the JDC in order to search this database. As usual, feel free to open a discussion about your problems on the java-linux@java.blackdown.org mailing list. 4.2.1. What Should I Report? Although it may not seem so, solving Linux JDK problems can sometimes be difficult because of the large variation of systems that are in use. Please do your best when reporting a bug to tell us all about your system, the code you're running, and anything else that can help. Here's a checklist of items to mention. 1. A careful synopsis of the problem. 2. Which JDK you're using. Type java -version to see. 3. Your Linux distribution (i.e. RedHat) and its version. 4. The LibC version you're using. Type ldconfig -D 2>&1 | grep libc | tail -1 to see. 5. The loader you're running. Type ldconfig -D 2>&1 | grep ld | tail -1 to see. 6. XFree86 Version. Type xdpyinfo | grep 'release number' to see. 7. The version of the Linux kernel you're running. Type uname -r to see. 8. JDC BugID if you've found one. 9. A URL where with some related Java code or binary data. 10. Your assessment of the problem's priority. 4.3. Are There Any Debugging Techniques I Can Try Myself? Try running the JDK java, appletviewer, and javac wrapper scripts like this: ______________________________________________________________________ $ sh -x $JAVA_HOME/bin/java -verbose -verbosegc -cs -verify ... ______________________________________________________________________ or this: ______________________________________________________________________ $ strace -f -s 256 $JAVA_HOME/bin/java ... ______________________________________________________________________ That last command will be very noisy, but you may be surprised what you learn from reading it. 4.4. That Didn't Help. What Else Can I Do? We've created a troubleshooting information collection script that you can download from http://www.place.org/~stevemw/java/FAQ/java-linux- info.sh and follow the instructions at the top of it. Mail its output to stevemw@place.org. 5. Details on Running The Blackdown JDK 5.1. I'm on <your favorite Linux distribution here> What Do I Need? 5.1.1. The glibc versus libc5 Problem The latest versions of the Blackdown JDK have their own built-in loader (libdl.so) and libc.so, which will hopefully make them more robust in most cases. Older versions of the JDK 1.1.5 (especially) are much more sensitive. Take a look in $JAVA_HOME/i386/green_threads/ to see these files. (You may remove them if you feel they are a source of trouble to you.) Karl Asha maintains a list of JDK-related library issues at: http://www.blackdown.org/java-linux/docs/libraries.html. In short, you need glibc-2.0.7 and glibc-devel-2.0.7 or higher on a glibc-based system such as RedHat 5.0 or Debian 2.0. There are RPMs for these on RedHat Intel systems at ftp://ftp.redhat.com/pub/redhat/current/updates/i386. For a libc5 system, you need libc.so.5.44 or greater, along with a recent libdl.so. You can find these at ftp://tsx-11.mit.edu/pub/linux/packages/GCC. For an in-depth discussion of this issue, see section ``What is glibc, and Why Does it Matter?''. 5.1.2. RedHat Installation Tips Download the glibc and ld updates described under http://www.redhat.com/support/docs/errata.html. 5.1.2.1. RedHat RPM Availability According to Sorin Lingureanu <sorin@tuiasi.ro>, JDK RPMs are to be found in ftp://ftp.redhat.com/pub/contrib. Levente Farkas has more information about running the Blackdown JDK on RedHat here: http://anna.inf.u-szeged.hu/java/java-rpm.html. 5.1.2.2. RedHat/RPM Environment Variable Issues In addition to the general problems described in section ``Environment Variables'', make sure that you don't have conflicting JDK_HOME, JAVA_HOME, and CLASSPATH environment variables set from scripts sourced from /etc/profile.d/ at login. This can especially be a problem when trying multiple versions of the JDK in succession. 5.1.3. Debian Paul Reavis <preavis@partnersoft.com> has an excellent page with details at http://www.partnersoft.com/~reavis/java/Debian-JDK.html. 5.1.4. Slackware In JDK versions 1.1.5 through 1.1.6v2 we've seen a problem with libc.so and libdl.so shipped with the JDK in $JAVA_HOME/lib/i386/green_threads conflicting with the system. Try removing these and then running Java. Please help by posting your experiences with the Blackdown JDK on Slackware. 5.1.5. Other Linux Distributions Check with http://nr.conexware.com/~zorzella/wine/FAQ2.htm to see if Luiz Otavio Lautenschlaeger Zorzella has additional information that applies to your platform. You're welcome to contribute what you know to the FAQ. 5.2. Is There Anything Different About Native Interfaces on Linux? Not really. The compilation flags may need to be different from what Javasoft recommends in the Solaris-oriented documentation. Also, there is a known problem with all green threads implementations and the JVM Invocation API, discussed in section ``Is There a Problem with Green Threads and the JVM Invocation API?''. There have been reports of problems with C++ IOStreams using libstdc++-2.7.x. Note that g++-2.8.1 and libstdc++-2.8.1 have been tested, and seem to work fine for several users on RedHat 5.0. 5.2.1. Compiling Library Code for JNI Ed Roskos <roskos@bellatlantic.net> gives us these instructions for C JNI: I've written a few shared libraries for use under both Linux and Solaris, and since a few people are curious about this, here goes: 1. Make sure you have run javah. Plenty of documentation on this exists. 2. You must first compile your C source files to object files, which end in ".o". Example: gcc -fPIC -c -I<java-header-path> file1.c -o file1.o You must replace <java-header-path> with the path to the include files for java-linux. 3. Create your library. This is not the same as creating an executable. Under Linux, use: ld -shared file1.o -o libMyLib.so If you have more than file1.o, just list them after file1.o. You can then, from Java, load your library as System.loadLibrary("MyLib"); Hope this helps. Ed Roskos roskos@bellatlantic.net And Duncan Roe <dunc@dimstar.cvsi.com> points us to the Texinfo docu- mentation for GNU C, and argues that -fPIC only makes a difference on the m68k, m88k and the Sparc. Evidently -fpic works in some cases (ELF?) on x86. 5.3. Is There a Problem with Green Threads and the JVM Invocation API? Yes, there's a known problem with Javasoft's user-level threads package (called green threads) and the Invocation API because of the way it wraps system calls. See section ``What are Green Threads?'' for more information on green threads. 5.3.1. Green Threads and Wrapped System Services Uncle George, Juergen Kreileder, and Bernd Kreimeier have encountered this problem, and through their discussion of it we have this list of references to consult for more information: o JDC Bug Parade bug ID at http://developer.java.sun.com/developer/bugParade/bugs/4040743.html o The Java Tutorial under "Invoking the Java Virtual Machine" at http://java.sun.com/docs/books/tutorial/native1.1/implementing/ o Rob Gordon's excellent Essential JNI published in 1998 by Prentice Hall PTR, ISBN 0-13-679895-0 Gordon suggests in Essential JNI on page 260 that: When building a Java-enabled application on Solaris and linking against the green threads version of libjava.so, you must defer system calls until after the call to JNI_Create- JavaVM. This is because the user-level threads package in libjava.so (green threads) defines its own system calls . . . And the JDK 1.1 Tutorial suggests that, "The first step toward getting this to work is always to link libjava.so into the executable *first*, even before libc.so . . ." 5.3.2. Hacking Around the System Service Wrappers On June 21, 1998 Uncle George posted these paraphrased comments: Actually, library calls are overridden, not system-calls. If you are savvy enough, you can call the system service your- self, and forget the library interface (i.e. instead of using select, try __select). But in doing so, the green threading . . . can be compromised, i.e. other threads won't be runnable until that service completes. The malloc()/free() bogus pointer messages are problems in trying to free a pointer twice, of which some "MALLOC" packages get terminally upset with . . . You may also be interested in the discussion of native threads in section ``Is There a Native Threads Port of the Blackdown JDK?''. 5.4. Kaffe and the Blackdown JDK 1.1 are Installed. Neither Work! After running javac HelloWorld.java and seeing this message: Failed to open object 'HelloWorld/java' Other people have reported error messages such as these: $ javac Failed to locate native library in path: /usr/lib Aborting. Daniele Lugli <danlugli@tin.it> reports: ...The javac which was giving the problem was /usr/bin/javac, that is the kaffe javac. Now that I moved $JAVA_HOME/bin ahead in my $PATH, both javac and java work, and I see a wonderful "Hello, World!". In other words, always check for conflicting environment variable problems. For details on how to do this, see section ``Environment Variables''. A very common cause for problems with Kaffe is having /usr/bin in your path ahead of $JAVA_HOME/bin. 5.5. I Have the Blackdown JDK 1.1.x and RMI is Giving Me Fits! Rich McClellan <richmc@entropy.ucsc.edu> reports that running the Blackdown JDK 1.1.5v7libc works better than the glibc version, and forwards this advice from Alexander V. Konstantinou <akonstan@cs.columbia.edu>: The problem is related to naming in /etc/hosts. This is a known Java problem in picking up the right name for the interface. Change the localhost name to your real machine name. This may cause problems with talk though ... 5.6. Help, I've Upgraded to ld.so-1.9.9 and Now the JDK Coredumps! Slackware users have found that removing the libdl.so.* and libc.so.* files from $JAVA_HOME/lib/i386/green_threads takes care of this problem. We don't know what causes it yet, though. 5.7. What's Wrong with Thread Priorities and the Console? You may be asking yourself this question if you share access to System.out or System.in among several threads. Jason Gilbert <jason@scott.net> has a reply to this question: Bernd Kreimeier wrote: > > Is there a problem with several threads using System.out > at the same time? A JDK problem? Or a Linux JDK problem? I believe it's a green threads JDK problem. jason -- Jason Gilbert | http://www.scott.net/~jason/ | http://www.homewood.net For a discussion of green threads, read section ``What are Green Threads?''. 5.8. Help, Java Said it Ran out of Memory! You have two strong candidates as causes for this problem. 1. Your program needs more than the default that the JVM allows. Memory limits can be set like this: java -ms16m -mx64m .... From the JDK documentation: -ms<number> set the initial Java heap size -mx<number> set the maximum Java heap size 2. You actually don't have enough virtual memory (the total of physical RAM and swap space) available. The free command can help you there. See the manual page for free(1). For the current minimum system requirements, see the discussion of them in section ``What System Configuration do I Need to Run the JDK?''. 5.9. How Do I Add Swap Space? See the manual pages for swapon(8) and mkswap(8). 5.10. Can I Display and Input Kanji with the Blackdown JDK? In addition to the information found here, you will certainly appreciate Dan Kegel's page, Fonts and Internationalization in Java found at http://www.alumni.caltech.edu/~dank/javafont.htm. You are encouraged to visit Javasoft's 1.1 discussion of this topic at http://www.javasoft.com/products/jdk/1.1/docs/guide/intl/fontprop.html, as well. Please be aware that these FAQ entries are extremely sketchy at the moment. If you have additional information about making CJK (Chinese, Japanese, and Korean) code work well with Java on Linux, please tell the FAQ maintainer. 5.10.1. Library Issues The following entries also relate more to situations that arise when you must settle on one set of libraries or the other, and you end up without being able to run some application or another because of unresolved symbols. Keep in mind that with their own builtin loader and libc, recent versions of the JDK shouldn't cause you to change your libraries at all. 5.10.1.1. Libc5 Systems Nozomi Matsumura <nmatsumu@can.bekkoame.ne.jp> has a suggestion that at least applied to earlier, libc5 versions of the JDK, and may still work. It involves making use of multi-byte character support provided in builds of libX11.so with the Xsetlocale(3) call. Matsumura-san points us at this fix provided by Hiroshi Hisamatsu <hisama2@asahi.email.ne.jp>, which is a small, shared library (liblocale.so) to explicitly specify the Kanji locale. It is available from http://www.asahi-net.or.jp/~nf6h-hsmt/jdk1.1.1-locale.tar.gz. More detail on this is available in Japanese at http://www.asahi- net.or.jp/~nf6h-hsmt/java.html. The fix also involves adding the following lines to your .java_wrapper file in $JAVA_HOME/bin: ______________________________________________________________________ LD_PRELOAD="$JAVA_HOME/lib/${ARCH}/${THREADS_TYPE}/liblocale.so" export LD_PRELOAD ______________________________________________________________________ Matsumura-san also mentions changing the locale specified by your environment variable LANG to ja, and says that ja_JP.{EUC,ujis} did not work. 5.10.1.2. Libc6 (glibc) Systems In addition to the properties hacks mentioned above (see section ``Libc5 Systems''), the inverse of what liblocale.so does is probably possible on glibc-based systems, if there's a problem (with some other application) at all. You may be able to simulate Xsetlocale(3) by wrapping setlocale(3) with it. For example, libc5 versions of XFree86 (see http://www.xfree86.org) handle locale with the Xsetlocale(3) call, but that changes under glibc to plain setlocale(3). See the setlocale(3) manual page for more information. 5.10.2. Entering Two Byte Kanji with XIM On July 14th, 1998, Nozomi Matsumura <nmatsumu@can.bekkoame.ne.jp> also submitted this information acquired from Minori Takagaki <lennen@st.rim.or.jp>, who was able to input and display Kanji using TextComponent. Takagaki was able to input directly using kinput2(XIM) or by cut&paste in Java applications and in appletviewer. Takagaki's environment is: o Slackware-3.4 + PJE-0.1(*1) o Kernel: 2.0.34 o libc: 5.4.38 o jdk1.1.6-v1-libc5 Takagaki said to use Japanese characters, you need to setup as described here: 1. Install Red Hat Motif 2.1 and X-TT(*2) 2. Modify font.properties.ja (to use X-TT fonts) 3. Get liblocale.so (see the discussion of this above in ``Libc5 Systems'') 4. modify .java_wrapper ___________________________________________________________________ export LD_PRELOAD=liblocale.so export LANG=ja export DYN_JAVA=1 # to use libXm.so.2 from RH Motif2.1 ___________________________________________________________________ 5. If using appletviewer, modify $JAVA_HOME/bin/i686/green_threads/appletviewer to use the dynamically linked java binary. X-TT is free a X font server for using Japanese TrueType Fonts. See http://www.ryukyu.ad.jp/~shin/linux/x-tt/. But some probelms occur: 1. The getText() function is O.K. but setText() is not. 2. Mouse drag selection is not well. Strings with Japanese charcters using TextField/TextArea are not selected correctly. 3. When a cursor moves in TextField, Japanese characters are often modified randomly. 4. When Japanese charcters are input in TextAreas, display timing is very strange. But getText() works correctly. Example: to input 'NIHONNGO abcdef' when keying 'ab', 'NI' shows; when keying 'cd', 'HONN' shows, etc. . . 6. Questions about Non-i386 Blackdown JDK Ports This section attempts to provide some additional information about non-Intel versions of the Blackdown JDK. At this time, Karl Asha has a more complete catalog of the different platforms available at http://www.blackdown.org/java-linux/ports.html. Help determining which JDK to download is available in section ``OK, Which Version of the JDK Should I Download?''. 6.1. What's the Status of the SPARC Port? On June 16, 1998 Johan Vos <johan@sesuadra.org> provided this summary of the current SPARC effort, which is based at http://sesuadra.org/~jdk/: Starting from JDK 1.1.5, the Intel and SPARC ports are based on the same code. The SPARC-specific issues are separated from the other linux-specific issues. Improvements and bug- fixes in the general source code can be implemented without having to re-implement the SPARC-specific code. As a conse- quence, most problems and updates on the Intel-JDK also occur on the SPARC-JDK. I try to synchronize as much as pos- sible with Steve's ports -- although licensing problems caused the JDK 1.1.6v1 release for SPARC to be a few days after the Intel-release. For the differences between static and dynamic linked versions -- of the Motif library --, the same remarks as for the Intel-release hold. Up to now, there is no port for glibc-systems -- since I don't have a glibc-system. Most likely, this porting will be done in the near future. 6.2. Is there an Alpha Port? Yes. Please see http://www.blackdown.org/java-linux/ports.html for more information. 6.3. Is there a PowerPC Port? Yes. Please see http://www.blackdown.org/java-linux/ports.html for more information. 7. General Questions about Java 7.1. Where Can I Learn More about Java? Here are a nuber of excellent starting points. o Elliotte Rusty Harold's comp.lang.java FAQ: http://sunsite.unc.edu/javafaq/javafaq.html o The Java networking FAQ: http://www.io.com/~maus/JavaNetworkingFAQ.html o Peter van der Linden's Java Programmer's FAQ: http://www.best.com/~pvdl/javafaq.html o Javasoft's Developer Connection FAQ: http://developer.javasoft.com/developer/techDocs/faqs.html 8. General Questions about Linux 8.1. Where Can I Find Linux FAQs, Mailing Lists, and Documentation? Here's a list of good places to start: o The Linuxdoc project: http://sunsite.unc.edu/LDP/. o The main Linux website: http://www.linux.org/. o Linux kernels and libraries: http://www.kernel.org/. 8.2. What is glibc, and Why Does it Matter? I'll explain what libc and glibc are in a bit, but first, let me say that the current Blackdown Linux JDK tries to avoid library incompatibilities by providing a dedicated dynamic loader and its own libc.so. And (I think) even before this change, the problem of "which of libc5 or glibc is needed" was theoretically only experienced on systems such as RedHat 5.0 and Debian 2.0 that had so rapidly moved to glibc. Other library conflicts are always bound to happen because of the variety of Linux versions and configurations there are. The UNIX "libc" is the core set of functions to which most utility and application code links. You can see references to libc in the intro(3) manual page. For your information, functions described in section two (see intro(2)) of the manual are all inside the kernel, whereas section three describes those which may be standard, but are stored in separate libraries. To view these pages, make sure your core manual pages are installed, and type man 3 intro, for example. In order to save disk space and memory, modern operating systems like Linux have taken to using "shared" libraries that don't move their contents into code which links to them during the build process. Although there is a /usr/lib/libc.a, most production code is linked to /usr/lib/libc.so, which is typically a link-editor script for selecting the actual libc.so (shared object) archive. In short, lots of programs on your system share code out of one or more files as they execute. To see what shared code an executable needs, there is an optional Linux utility named ldd(1). If it's on your system, you can type ldd PROGRAM to see its shared libraries. Here's an example: ______________________________________________________________________ $ ldd /bin/ls libc.so.6 => /lib/libc.so.6 (0x40003000) /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00000000) ______________________________________________________________________ The older (and still most common) Linux libc was known as "libc5." The GNU/Linux development community sought to improve on it by adding thread-safety where possible, 64-bit support, better POSIX and XPG4.2 compliance, superior organization of the library sources, and multi- byte character locale support. These and other changes will bring even more robustness and quality to the Linux development environment. Although the changes are inconvenient to us sometimes, the end result should be worth it. The new library is now called "glibc" because it's a library common across Linux and HURD, and enjoys a broad base of GNU developer contributions. (I don't know how much of the earlier Linux libc software was derived from GNU libc, which has been around for quite a while on its own, I think.) For more information on GNU libc, see http://www.imaxx.net/~thrytis/glibc/. Since C is central to the history and development of UNIX and Linux, you might enjoy the links found on http://www.dundee.ac.uk/~bmsimpso/work/C-Programming/ as well. 9. Compiling the Blackdown JDK from Source 9.1. Can I Build Java Myself? Building the JDK on Linux with patches supplied by Steve Byrne is fairly straightforward. See http://www.blackdown.org/~sbb for the diffs and some additional details. I encourage you to read README.linux.src from the patched source distribution if you plan to undertake this project. You will need to sign a license agreement with Javasoft in order to download the sources. See section ``Could You Give Me a Pointer to Sun's Licensing Agreement?'' below for details. 9.2. Could You Give Me a Pointer to Sun's Licensing Agreement? In order to obtain the JDK sources, first you must read, sign, and FAX in an agreement with Sun. The agreement can be found at http://www.javasoft.com/nav/business/source_form.html. 9.3. How do I Build the JDK Now that I Have the Source? Please read the http://www.place.org/~stevemw/java/FAQ/README.linux.src file. 9.4. What about Motif? Don't I Need That? You can build the JDK against Lesstif, the Hungry Programmers' GNU copylefted implementation of the Motif API. For more information, visit their website at http://www.lesstif.org. Make sure you get the "current" distribution. They are very responsive to accurate bug and problem reports. On the other hand, a number of Motif developer library vendors exist for Linux systems. I recommend you read the Motif comp.windows.x.motif news group FAQ. You can find it here: http://www.rahul.net/kenton/faqs/mfaq_index.html. 9.5. When I Build and Install, I Get Unsatisfied Link Errors at Run- time! Make sure you're building all the targets Steve Byrne suggests in http://www.place.org/~stevemw/java/FAQ/README.linux.src. Here's an example: ______________________________________________________________________ make DESTDIR="$ALT_JAVAHOME/jdk116v2b" RELEASE="MY-JDK1.1.6-V2B" \ appletviewer jre_only 2>&1 | tee MakeOut-V2B1-BUILD-01 ______________________________________________________________________ In this example, I have ALT_JAVAHOME set to the javasrc/build, just above the genunix/ target directory. You should be able to set ALTMO- TIF_DIR to where you've installed Lesstif. Note: you ought to have ALT_BOOTDIR set to a running JDK 1.1, and I build with CLASSPATH and JAVA_HOME unset. 9.6. Can I Try Builds of the Latest JDK Port in Development? Please stay tuned to the mailing list for announcements. 10. About the People Behind the Blackdown JDK 10.1. Who Ported the Blackdown JDK? Randy Chapman <chapman@wilbursoft.com> did the original port of the Solaris JDK 1.0 to Linux on the i386. Steve Byrne has done much of the work on the Intel port of 1.1. Quoting Steve Byrne from http://www.place.org/~stevemw/java/FAQ/README.linux Special thanks to Johan Vos (Sparc Linux port), Chris Sea- wood (GLIBC), Karl Asha (who gave us blackdown, thanks Karl!) Kevin Buettner, Scott Hutinger, Kevin Hendricks, Brian Keller, Philippe Laliberte and the rest of the PowerPC porting team -- these guys really fixed a *lot* of generic JDK bugs -- the 1.1.5 port is *much* better as a result of their hard work. Dan Powell and Rich Cannings have been very gracious to take over the administrative duties and to pro- vide a site (and domain name) dedicated to java-linux -- thanks! And again: Neal Sanche fixed the thread creep bug. Thanks, Neal! Please pass on historical information to the FAQ maintainer. 10.2. Who is Steve Byrne? Steve has some auto-biographical information on his web page at http://java.sun.com/people/sbb/index.html. 10.3. Who is Karl Asha? Karl has this response: Not too much to say...some time back in 1995 I wanted so much to have java on a linux box so I started harassing peo- ple I knew to work on it. I put together the web site, the mailing lists, etc, helped out a little here and there with the port, and things just bloomed :) 11. Information on the Java-Linux FAQ Itself 11.1. Who Maintains the FAQ? Stephen Wynne is the current FAQ maintainer. However, answers to questions found in this document are from a variety of participants on java-linux@java.blackdown.org. If you have any comments, clarifications, or corrections, please send them to Stephen Wynne <stevemw@place.org>. If you have something to add, please send E-mail to the list itself. 11.2. Where Can I Get a Copy of the FAQ? Most-recent copies of this FAQ can currently be found at http://www.place.org/~stevemw/java/FAQ/FAQ-java-linux.html. Here's the text version of this document: http://www.place.org/~stevemw/java/FAQ/FAQ-java-linux.txt. The PostScript "letter" version: http://www.place.org/~stevemw/java/FAQ/FAQ-java-linux.ps. The PostScript "A4" version: http://www.place.org/~stevemw/java/FAQ/FAQ- java-linux-a4.ps. Full source for the original at http://www.place.org/~stevemw/java/FAQ/. The FAQ is regularly mirrored to http://www.blackdown.org/java- linux/docs/faq/FAQ-java-linux.html. 11.3. Please Help the FAQ Maintainer! The FAQ maintainer is looking for the following information: o Slackware (and other Linux distribution) setup issues. o Any CJK setup tips and suggestions you may have. o Your experiences with the Java Webserver. o Tips and problems using your window manager with the Blackdown JDK. o <That burning question you just spent hours to answer yourself!> 11.4. Are there Any Plans for Automating the FAQ? At this point, the FAQ maintainer has considered FAQ-o-matic (found at http://www.dartmouth.edu/cgi-bin/cgiwrap/jonh/faq.pl) and Wiki web (found at http://c2.com/cgi/wiki). Your comments and suggestions would be appreciated. 11.5. Caveat Emptor This document may contain technical information that is incorrect, out-dated, and may unintentionally misrepresent the opinions of java- linux@java.blackdown.org participants. Neither the FAQ maintainer nor the members of the mailing list make any warranty with respect to its usefulness or safety. 11.6. Terms of Use This document is copyright 1998 by Stephen M. Wynne. You may use, disseminate, and reproduce it freely, provided you: o Do not omit or alter this copyright notice. o Do not omit or alter or omit the version number and date. o Do not omit or alter the document's pointer to the current WWW version. o Clearly mark any condensed, altered or versions as such. These restrictions are intended to protect potential readers from stale versions. 11.7. Acknowledgements This FAQ's content and structure was inspired by several documents produced by Eric S. Raymond. Eric also maintained an early HOWTO regarding Java on Linux. It's archived at http://sagan.earthspace.net/~esr/faqs/java.html. The FAQ was produced directly from SGML with the SGML tools package v0.99.0, using the LINUXDOC.DTD.