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Java on Linux HOWTO maintained by Eric S. Raymond, <esr@snark.thyrsus.com> v1.0, 10 December 1995 This document describes how to get started with Java and HotJava under Linux, as either a user or a programmer. 1. Introduction This document is a Linux-centric introduction to the world of Java and HotJava. These technologies are rapidly evolving, and we welcome contributions from anywhere. Places in this document that are in serious need of checking or filling out are bracketed with *** ***. Also see the ``To Be Added...'' section below. Please help us improve this HOWTO. 2. General Questions About Java and HotJava This section is a general (non-Linux-specific) introduction to Java and HotJava. 2.1. What are are Java and HotJava and why are they interesting? Java is a network-aware language superficially resembling C++, but much smaller and more compact and cleanly designed. It's an unlimited-extent language with garbage collection like Lisp, but with strong type checking. It includes lightweight processes (threads) as a native facility and has powerful network-security features. So far, its major application is the HotJava browser, but it holds considerable promise as a general-purpose application language. HotJava is a WWW browser written in Java. Its major advance over other browsers is that it knows about a new HTML construct called an APP, which is some Java class that executes on the client machine. Thus, WWW documents written with Java in mind can have "live" code objects embedded in them, as opposed to just data. The ability to safely pass around code objects probably represents the most significant advance in WWW technology since the first release of Mosaic. At minimum, it delivers an extensible Web browser that won't need perpetual upgrading to handle new image formats and tag types. 2.2. Where do Java and HotJava come from? Who can use them? Java and HotJava were developed at Sun Microsystems by a team headed by James Gosling (well known as the designer of Gosling Emacs and NeWS). The last time Sun tried to set a major technical standard was NeWS, its Network Window System. Though NeWS was pretty universally conceded to be technically superior to X, X won because its sources were freely redistributable. Sun learned from this mistake, and has made Java/HotJava much more generally available; the sources can be downloaded under a fairly relaxed license (see ``Java as Freely Redistributable Software''). Sun is encouraging ports to non-Sun environments. Netscape now interprets Java. Microsoft licensed the technology in early December 1995. So it appears that Java support will probably become universal in 1996. Java used to be called Oak. HotJava was once known as WebRunner. 2.3. How mature is Java? Java is currently (December 1995) in late beta at Sun. The Java environment API defining its access to the host OS and windowing system has allegedly been semi-frozen -- it may be extended, but won't be incompatibly changed. The 1.0 version of this FAQ is being issued along with the beta 1.0 Java Developer's Kit (JDK) for Linux, ported by Randy Chapman. Significant holes are known to exist in the Java security implementation. It is not yet a good idea to use Java for sensitive applications. These problems are expected to be fixed in the production (post-beta) releases. 2.4. Where can I find documentation on Java and HotJava? Sun maintains an extensive HTML web of Java and HotJava-related documents at <http://java.sun.com>. These documents are mirrored at <http://java.blackdown.com> and elsewhere; see Sun's list of mirror sites. 2.5. Yes, but where can I find paper documentation? SunSoft Press's official series of Java books is in the production pipeline at Addison-Wesley. Some details about these can be found in the comp.lang.java FAQ <http://www.city-net.com/~krom/java-faq.html>. O'Reilly Associates is working on its own series of Java books in cooperation with Sun. These are expected to include (at least) a "Nutshell Guide To Java", a language reference, a class library reference, and a book on the underlying byte-code virtual machine. (Full-disclosure statement: Your HOWTO editor has been invited by O'Reilly Associates to serve as primary technical reviewer for this series, and will be paid for that work.) Per information on Sun's java web pages, SAMS will be publishing in December, 1995, "Learing Java in 21 Days". I checked with the local (Vienna, VA) Computer Learning Center bookstore; they expect to receive their first shipment sometime in mid-late December. One of our contributors, browsing his local Bookstop/Barnes & Noble/Borders, came up with 3 books already out: o One called 'Java in 60 minutes' that looked like a pretty strict syntactic description (about $20). o One from SamsNet called just `Java' (about $20). o One by Tim Ritchey called `Java!' that includes a CD-ROM (about $35). Our informant continues: "I bought the 3rd one (by Tim Ritchey). Paper leadtimes being what they are, the CD-ROM only has alpha stuff, though it mentions that the beta version might be out by the time you read it and suggests java.sun.com as a place to get more recent information. Other than that, it's pretty good, even to pointing out that `well, it's pointless for me to spam you with pages and pages of API descriptions because 1) it would quadruple the size of the book and 20 they're still ch anging and 2) you can get that info online at ...etc'" 2.6. Where can I find on-line collections of Java code? WWW archives of applets are available at the following locations: o <http://java.sun.com/> o <http://www.applets.com/> o <http://www.gamelan.com/> o <http://www.javasoft.com/applets/applets.html> Most of the applets on these pages come with source code, and programmers are invited to use them. Pointers to others may be available in the comp.lang.java FAQ <http://www.city-net.com/~krom/java-faq.html>. 3. Java as Freely Redistributable Software Many Linux programmers are attached to producing freely redistributable software (FRS), and try to avoid committing a lot of time to tools for which sources are not generally available. In this section, we discuss Sun's and Java's relationship with the FRS world. (Warning: I am not a lawyer. I am neither employed by, nor an agent of, nor a stockholder in, Sun Microsystems. This section is based on my interpretation of the current copyright law and the Sun licensing language. Treat this as an introduction; the Sun licensing page, <http://www.blackdown.org/Java/licensing.html> is definitive. If you are in serious doubt about what it means, consult an attorney.) 3.1. Are Java programs and applets freely redistributable? They are if you write them and choose to make them FRS through some mechanism (such as the GPL, or a BSD-style license, or declaring them public domain). 3.2. What can I do with Java implementation binaries? The Sun licensing page has this to say: The unmodified Java and HotJava binary releases may be redistributed free of charge in both commercial and non- commercial applications. Also: Companies or individuals who wish to create a new port of the Java language have the right under this agreement to post the binaries of that port to the Internet for use by others, as long as the port is free of charge and passes the publicly available test suites. (Test suites will be avail- able sometime in the first half of 1996.) The "diffs" may also be posted on the web as long as the underlying source code is not posted. The Java source code is So if you've got a working Java or HotJava binary, you can give it to your buddies. Or put it on a CD-ROM. Or do anything except patch it and represent the patched version as Java. (This is reasonable. Sun obviously can't leave itself without recourse against Trojan horses sailing under the Java banner.) Binaries are FRS. 3.3. Which parts of the Java sources are freely redistributable? According to Sun's licensing page, none of it is. But that sounds harsher than it is. In practice, anyone can get the Java and HotJava sources for educational, porting, and non-commercial purposes by filling out a Web form which obligates them not to redistribute the sources. And the agreement does permit redistribution of diffs against the sources. The only circumstance that requires you to sign a commercial license with Sun and pay them money is if you want to use the sources in a commercial product. In particular, the way the language is written, it's within the letter and spirit of the agreement for you to sign Sun's noncommercial source license, snarf the source, port it, and give away the results as completely unencumbered freeware! Sun says that its primary purpose in keeping as much control as it has is to keep the language from mutating into incompatible dialects. The license language supports this; it seems to have been designed to allow hackers to play for free. 3.4. Is anyone cloning Java in freely redistributable source? Not that we know of, yet. The Sun licensing page says: The specifications for the Java Language and the Java Vir- tual Machine are OPEN and are copyrighted by Sun Microsys- tems, Inc. Reimplementations of the Java Compiler or the Java Runtime Interpreter are permitted without requiring a license from Sun provided such implementations are created directly from the published specifications and without the direct or indi- rect use of Sun's own implementations or other intellectual property rights, including trademarks. So if you want to go to the effort of creating a Java clone from the published specifications that is FRS, and calling it "Mr. Coffee", Sun won't stop you. If Java becomes as popular as everybody expects, it will certainly be cloned. (The editor of this HOWTO hereby announces his availablity to help write either the Mr. Coffee compiler or the byte-code interpreter or both, as soon as suitable specification documents become available.) 3.5. Are there any FRS Java Tools? There is a GNU Emacs mode for editing Java. You can fetch it from <ftp://java.sun.com/pub/java/contrib/emacs>. 3.6. What is Sun's attitude towards FRS Java implementations and tools? Sun people use the term "rogue port" for Java implementations that either (a) are performed outside Sun, or (b) don't rely on Sun- licensed code (sometimes the term seems to mean one thing, sometimes the other). They seem to think some of these already exist, but we don't know where they are, nor if they are FRS. They're pretty relaxed about the situation. Sun has a Java validation suite. They have said they'll certify any Java port that passes it. (Whether this validation will cost money is unknown, but Sun says in writing that the suite wil be "publicly available" in 1996, which at least hints that it will not.) They're prepared to certify rogue ports, though this apparently hasn't happened yet. 4. Java On Linux Questions Here you can learn the nuts and bolts of getting Java running on your Linux. 4.1. Are Java and HotJava included in any of the Linux distributions? No, not yet, but expect it any week now. 4.2. How can I get the latest Java distribution for Linux? Look in <ftp://java.blackdown.org/pub/Java>. The latest Java-for- Linux can be downloaded from there. You should browse the <ftp://java.blackdown.org/pub/Java/README> first. The files you'll need are linux.jdk.common.tar.gz and one of either linux.jdk.x86-static-motif-bin.tar.gz ot linux.jdk.x86-shared-motif- bin.tar.gz, depending on whether you have Motif shared libraries on your system. This port (from the Sun sources by Randy Chapman) is the one that's referred to (as the JDK) elsewhere in this HOWTO. 4.3. What environment will I need to run Java? For starters, you need an ELF-based Linux. There is no a.out support, and at the speed the Linux world is switching over to ELF there is not likely to be any in the future. You need a 1.2.13 or later kernel. Kernels 1.2.12 and older seem to have a bug in getcwd(3) that tanks bin/javac because it doesn't check the getcwd(3) return code. You'll need these pieces: o libc.so.5 => /lib/libc.so.5.2.16 o libX11.so.6 => /usr/X11/lib/libX11.so.6.0 o libXt.so.6 => /usr/X11/lib/libXt.so.6.0 o libXext.so.6 => /usr/X11/lib/libXext.so.6.0 o libXpm.so.4 => /usr/X11/lib/libXpm.so.4.3 o libdl.so.1 => /lib/libdl.so.1.7.9 The C and X support libraries may be in your Linux already. If you don't already have it, get libc.5.2.16.bin.tar.gz from <ftp://tsx-11.mit.edu/pub/linux/packages/GCC/>. Uncompress and untar and copy the files in the lib subdirectory of the top level of the hierarchy to /lib. If you don't have a current version of ld.so (or libdl.so.1.7.*) you will need to update. ld.so.1.7.9 and .11 will work; .10 and other early versions will not. Get ld-so.1.7.11.tar.gz from <ftp://ftp.ods.com/linux/>; Uncompress and untar it and run instldso.sh which is in the top level of the resulting hierarchy. You can get an Xpm library that will work from <ftp://sunsite.unc.edu/pub/Linux/libs/X/libXpm.3.4f-ELF.tar.gz>. 4.4. Do I need Netscape? Can I use Netscape? Yes, you need Netscape. HotJava isn't yet available for the beta release. Randy Chapman says: Sun massively changed the awt interface when they shipped the beta JDK and have not yet converted HotJava to it. They have promised they will, and it should work great with linux-jdk when they release it. It's unknown when this will happen. As of December 1995 only Netscape 2.0b3 is Java-aware. It is available at ftp1-7.netscape.com (i.e. at ftp1.netscape.com, ftp2.netscape.com,... etc.) The file to get is /2.0b3/unix/netscape- v20b3-export.i486-unknown-linux.tar.Z. Note that Netscape 2.0b3 will run on an a.out system, so it is, in theory, possible to write your java app, give it to someone else to compile (like maybe the BlackStar Public Compiler <http://mars.blackstar.com>), and see the output on your system. If you want more than that, get an ELF system. Adam Smith writes: A tiny amount of fudging (moving one file) is required to make Netscape run from the distribution: it will crash when loading a page with Java applet(s) if Netsacape's condensed single-file version of the *.class files is not first in the CLASSPATH environement variable, and I don't know the effect on Java/HotJava of having that in the path (since the archived classfile format is irregular, I suspect it might work). I have run the Netscape successfully on my Slackware 3.0 system. Steve Greene writes: There's been some discussion on the java-linux list on how to configure Java and Netscape to make it pick up your local applets for viewing. The consensus seems to be that you need to add the path to the applet added to the CLASSPATH environment variable, or run a local Webserver and access the applets through the local Webserver as if it were over the 'net; you may also need to be connected to be able to find java.sun.com (I suspect but do not know that this is a holdover from the alpha HotJava browser, and is simply to ensure the browser could find the "stock" Sun class libraries on there site. I haven't tried any of this yet, so your milage may vary. 4.5. What mailing lists or newsgroups exist for supporting Java on Linux? o java-linux (Maintained by karl@blackdown.org) Discussions and developments concerning the port of Java to the Linux operating system. Email to java-linux-request@java.blackdown.org with the word `subscribe' in the subject to be added to the list. o java-linux-announce (Maintained by karl@blackdown.org) Moderated list for announcements concerning the Java-Linux porting projects. Please send e-mail to java-linux-announce- request@java.blackdown.org with the word subscribe in the subject, to be added to the list. o comp.lang.java Newsgroup for general Java discussion. o alt.www.hotjava Newsgroup for discussion of the HotJava browser. 5. Building the Linux Java port on stock Linuxes In this section, we collect recipes sent to us for building Randy Chapman's Java port on various current Linux distributions: 5.1. Slackware distribution ELF kernel 1.2.13. John Franks <john@math.nwu.edu> writes that he succeeded with the following steps: o Get linux-x86.jdk.pre2.static-motif.tar.gz from <ftp://www.blackdown.org/pub/Java/linux/> and uncompress it and untar it. (The filenames you must fetch have changes for the 1.0 beta JDK.) o Get libc.5.2.16.bin.tar.gz from ftp://tsx-11.mit.edu/pub/linux/packages/GCC/ Uncompress and untar and copy the files in the lib subdirectory of the top level of the hierarchy to /lib. o Get ld-so.1.7.11.tar.gz from ftp://ftp.ods.com/linux/ Uncompress and untar it and run "instldso.sh" which is in the top level of the resulting hierarchy. You should now be able to compile and try the "hello world" program and applet from Sun following the instructions at <http://java.sun.com/progGuide/index.html>. 5.2. RedHat 2.1/Caldera Preview 2 Steve Greene <sgreene@access.digex.net> reports success doing the following steps. I have edited the recipe slightly, so blame any mistakes on me. The `JDK' he refers to is the Chapman port of the Java Developer's Kit. o From ftp.ods.com, get the rpm available for ld.so.1.7.11. Check any RedHat mirror site for: /pub/mirrors/redhat-2.1/updates/RPMS/ld.so-1.7.11-i386.rpm I know it is available at ftp.pht.com, ftp.caldera.com. and is probably at the other RedHat mirrors as well. Grab it, and do `rpm -ivh ld.so-1.7.11-1.i386.rpm' on your system. o Get the tar file(s) for the statically-linked JDK. Untar it from a convenient point. I put mine in /usr/local, so the untar creates /usr/local/java/.... o So you can run java as someone other than root (this is a good idea!), do `chmod 666 /dev/zero'. Red Hat and Caldera have the wrong permissions set on this device out of the box. o If you haven't already, run ldconfig as root to load the new libraries. If you do "ldconfig -v" you can verify you have all the libraries loaded. (At least we don't have to build an ELF system first!) o Make sure you're logged in as a user (e.g. non-root). Start X- windows, open an X-Term, and try something! Steve adds: If I understand the on-line notes correctly, bin/java is a script that calls the run-time Java interpreter (used to run Java applications), bin/javac is a script for the Java compiler for compiling applications and applets, and bin/appletviewer is a script that allows you to look at an exisiting (compiled) applet. A number of demonstration applets are in the demo directory. The applet viewer requires a file name. I haven't figured out the correct syntax to run bin/appletviewer directly, but I figured out an alternative by examining the script file. To run a demo, I enter this command from the top of my Java directory tree, /usr/local/java on my system): bin/java sun.applet.AppletViewer demo/<directory_name>/exampleN.html where <directory name> is the subdirectory off demo, and N is the number of the example file (some directories have more than 1). The first time you run Java, a license screen (which reminds me of Netscape's) is displayed. I've started the tutorials available from Sun's java site and the similar one put out by the NTMUG. I've discovered some problems with the syntax in Sun's tutorial, so I've been following the NYMUG tutorial instead for now. 6. Notes on Known Problems Steve Greene tells us: These are problems I ran into and how I fixed them (e.g., this is my "Been There, Done That" troubleshooting list): 1. This is my parochial list on thw problems I had; it is not a generic troubleshooting list! 2. It's probably RedHat/Caldera - centric. 6.1. An error message refers to /dev/zero Go root and do `chmod 666 /dev/zero'. 6.2. SEGFAULT Occasionally, you may get a screen full of error messages, and the system cheerfully fills up your swap space and locks-up. You're probably missing a library someplace. Rerun ldconfig -v and see what's missing. Perhaps LD_LIBRARY_PATH or CLASS_PATH is not set. Finally, some applets are buggy or lock up the Linux JDK. (BTW, you can stop the lock-up by having another Xterm open with top running; use top to kill the java process BEFORE it fills up swap and hangs your system!) Java seems to want lots of resources, so I'd keep the number of running/open apps on my desktop to a minimum. It will load on a 486DX-2-75 with 8 Mbytes RAM and 16 Mbytes swap (it'll take a minute, though). I was able to get two animation applets running simultaneously (sort of) before my system ran out of swap space and hung. 6.3. bin/java, bin/javac, or bin/appletviewer gives you a help screen You left out some command-line parameter. 6.4. Problem Logging Finally, Joey Oravec tells us that HotJava keeps a log of what it does and any problems in encounters. If you're up to diagnosing something yourself, look at $HOME/.hotjava/weblog in the user's home directory. That file will make it more obvious if you're perhaps missing a library or something. 7. Related Resources For general information on Java, there is a FAQ maintained on the comp.lang.java newsgroup; it is available at <http://www.city- net.com/~krom/java-faq.html>. There is an older FAQ-style document by Joey Oravec joey@sun.science.wayne.edu <mailto:joey@sun.science.wayne.edu> which primarily refers to the alpha release. You can find it at <http://www.science.wayne.edu/~joey/java/linux.html>. At some point these documents may merge. Here are some Java-related pages: o Karl Asha's General Linux Java Page <http://substance.blackdown.org/java-linux.html> LinuxJava Mailing List <http://homer.ncm.com/java-linux/> Netrek for Java <http://www.cs.utexas.edu/users/hiep/netjav.html> Blue-Skies for Java <http://cirrus.sprl.umich.edu/javaweather/> 8. To Be Added... o More recipes for specific Linux variants. 9. Acknowledgements Grateful acknowledgement is made to all contributors, including: o John Franks <john@math.nwu.edu> o Zachary DeAquila <zachary@zachs.place.org> o Steve Greene <sgreene@access.digex.net> o Dave Dittrich <dittrich@cac.washington.edu> o Dave Flanagan <dave@ora.com> o Joey Oravec <mailto:joey@sun.science.wayne.edu> o Adam Smith <aws@cs.brown.edu> This version incorporates Steve Greene's rumored but never-published Red Hat/Caldera mini-HOWTO. I've also swiped some stuff I consider useful off Joey Oravec's page -- special thanks to him. For other HOWTOs and FAQs I maintain, see my home page at <http://www.locke.ccil.org/~esr/home.html>.