This document describes how to get started with Java and HotJava
under Linux, as either a user or a programmer.
* Menu:
* Introduction::
* General Questions About Java and HotJava::
* Java as Freely Redistributable Software::
* Java On Linux Questions::
* Building the Linux Java port on stock Linuxes::
* Viewing Applets::
* Notes on Known Problems::
* Related Resources::
* To Be Added--::
* Acknowledgements::
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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 *Note To Be
Added--:: section below. Please help us improve this HOWTO. Send
updates and change requests to .
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General Questions About Java and HotJava
****************************************
This section is a general (non-Linux-specific) introduction to Java
and HotJava.
* Menu:
* What are are Java and HotJava and why are they interesting?::
* Where do Java and HotJava come from? Who can use them?::
* How mature is Java?::
* Where can I find documentation on Java and HotJava?::
* Yes but where can I find paper documentation?::
* Where can I find on-line collections of Java code?::
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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
static type checking (it's been aptly described as "Smalltalk with sane
syntax"). 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
APPLET, 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.
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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 *Note 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.
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How mature is Java?
===================
On December 12 1995 Sun released the `Beta 2' version of Java. 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.
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Where can I find documentation on Java and HotJava?
Sun maintains an extensive HTML web of Java and HotJava-related
documents at . These documents are mirrored at and elsewhere; see
Sun's list of mirror sites.
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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 .
Several Java early-adopters have recommended "Hooked on Java" by the
members of the Java team. "Well written, though I'd appreciate
something less basic" was one comment.
O'Reilly Associates is working on its own series of Java books in
cooperation with Sun. These will 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 is being paid
for that work.)
SAMS has a book called "Learning Java in 21 Days". No revieww yet.
One of our contributors, browsing his local Bookstop/Barnes &
Noble/Borders, came up with 3 books already out:
* One called 'Java in 60 minutes' that looked like a pretty strict
syntactic description (about $20).
* One from SamsNet called just `Java' (about $20).
* 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'"
Dave Dittrich writes: I'd say that "Java in 60 minutes" may take you
60 minutes to read, but won't teach you how to program in Java in 60
minutes (surprise, surprise!) It looks to me like "Java in 60 minutes"
is one of the many attempts be first to market with a book on a hot
topic. It didn't seem to include much more than you can find right now
on the Web, including lots of text that looks like it was lifted
Dave continues: Same thing with "Java!", only the latter goes into
much more detail on object oriented programming concepts, etc. Someone
pointed me to another text book that is equally as good at covering
data/method abstraction and other object oriented programming concepts,
which is "Structure and Interpretation of Computer Programs" by
Abelson, Sussman and Sussman (MIT Press).
Final caveat: at this point (January 1996), it is probly a good idea
to stay away from the Ritchey book or anything else based on the alpha
API. The beta API is substantially different, and the
soon-to-be-released Java 1.0 will have its own differences.
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Where can I find on-line collections of Java code?
WWW archives of applets are available at the following locations:
* * * * 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 .
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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, is
definitive. If you are in serious doubt about what it means, consult an
attorney.)
* Menu:
* Are Java programs and applets freely redistributable?::
* What can I do with Java implementation binaries?::
* Which parts of the Java sources are freely redistributable?::
* What is Sun's attitude towards FRS Java implementations and tools?::
* Is anyone cloning Java in freely redistributable source?::
* Are there any FRS Java Tools?::
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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).
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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 available 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.
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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 resulting binaries 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.
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What is Sun's attitude towards FRS Java implementations and tools?
The specifications for the Java Language and the Java Virtual
Machine are OPEN and are copyrighted by Sun Microsystems, 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 indirect 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, Sun won't stop you.
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.
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Is anyone cloning Java in freely redistributable source?
There is a clone of the Java compiler in early development. It's
called guavac. You can find more information at
There is a rumor afloat that Cygnus Software's GROW project has
plans for a Java byte code interpreter to be issued under GPL.
However, they haven't yet responded to a query about this. You can get
details on the GROW project at .
Erik Troan of Red Hat is attempting to put together a development
group to do the rest of the job. Right now it looks like Erik will do
the class library and your humble editor will do the byte-code
interpreter (if Cygnus hasn't gotten there first). This project has
been tentatively named "Mr. Coffee". Your editor would now prefer to
call it "joe" (for Java Open to Everyone) but that name is taken.
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Are there any FRS Java Tools?
=============================
There is a GNU Emacs mode for editing Java. You can fetch it from .
Note: this mode assumes you're using c++-mode.el, and won't work with
the cc-mode.el distributed with Emacs 19.
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Java On Linux Questions
***********************
Here you can learn the nuts and bolts of getting Java running on
your Linux.
* Menu:
* Are Java and HotJava included in any of the Linux distributions?::
* How can I get the latest Java distribution for Linux?::
* What environment will I need to run Java?::
* Do I need Netscape? Can I use Netscape?::
* What mailing lists or newsgroups exist for supporting Java on Linux?::
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Are Java and HotJava included in any of the Linux distributions?
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How can I get the latest Java distribution for Linux?
Look in . The latest Java-for-Linux can be downloaded from there.
You should browse the 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.
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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:
* libc.so.5 => /lib/libc.so.5.2.16
(The standard C library)
* libX11.so.6 => /usr/X11/lib/libX11.so.6.0
(The base X11R6 library)
* libXt.so.6 => /usr/X11/lib/libXt.so.6.0
(The Athena toolkit library)
* libXext.so.6 => /usr/X11/lib/libXext.so.6.0
(The X extensions library)
* libXpm.so.4 => /usr/X11/lib/libXpm.so.4.3
(The X library for pixmap handling.)
* libdl.so.1 => /lib/libdl.so.1.7.9
(Linux dynamic-loader support)
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 .
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 ; 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 .
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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.
Netscape versions starting from 2.0b3 is Java-aware. It is
available at ftp$1-7$.netscape.com (i.e. at ftp1.netscape.com,
ftp2.netscape.com,... etc.) Version 2.0b4 will allow you to read
applets from file: URLs, 2.0b3 didn't. This should be a big help for
folks with small-memory machines (they don't need an httpd running).
Note that Netscape 2.0b3 or 4 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 ), and see the output on your system. If you
want more than that, get an ELF system.
Make sure CLASSPATH is `not' set before running netscape; having it
set seems to crash Netscape, and if you follow the directions below it
won't need tweaking.
The Linux Netscape port has a few known problems. It doesn't do
sound. Only 8-bit displays work; 16bpp displays yield crashes. The
2.0b3 version occasionally yields bus errors when caling the dispose
method for frames. While it's pretty robust otherwise, Gamelan's
`Impressionism' applet is known to crash it.
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What mailing lists or newsgroups exist for supporting Java on Linux?
* `java-linux' (Maintained by karl@blackdown.org) Discussions and
developments concerning the port of Java to the Linux operating
system. Email to
with the word `subscribe' in the subject to be added to the list.
* `java-linux-announce' (Maintained by karl@blackdown.org) Moderated
list for announcements concerning the Java-Linux porting projects.
Please send e-mail to
with the word subscribe in the subject, to be added to the list.
* Newsgroup for general Java discussion.
* Newsgroup for discussion of the HotJava browser.
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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:
* Menu:
* Slackware distribution ELF kernel 1-2-13-::
* RedHat 2-1/Caldera Preview 2::
* Unifix::
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Slackware distribution ELF kernel 1-2-13-
=========================================
John Franks <john@math.nwu.edu> writes that he succeeded with the
following steps:
* Get linux-x86.jdk.pre2.static-motif.tar.gz from
and uncompress it and untar it. (The filenames you must fetch
have changes for the 1.0 beta JDK.)
* Get libc.5.2.16.bin.tar.gz (binary distribution, not source) from
Uncompress and untar and copy the files in the lib subdirectory of
the top level of the hierarchy to /lib. Make sure that
/lib/libc.so.5 is a symlink to this file.
* 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 .
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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.
* From a Red Hat mirror site, get the rpm available for
ld.so.1.7.11. To find it, check any RedHat mirror site for:
where <directory name> is the subdirectory off demo, and N is the
number of the example file (some directories have more than one).
Steve Greene says: 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.
The appletviewer expects as an argument, an html file with an APPLET
tag inside it.
For example, if your html file Hello.html looks like:
<HTML>
<HEAD>
<TITLE> Hello test program </TITLE>
< /HEAD>
<BODY>
This is an appletviewer test
<APPLET CODE="Hello1.class" WIDTH=150 HEIGHT=25>
< /APPLET>
< /BODY>
< /HTML>
(If you see "< /" in the above, ignore the space. It's a workaround
for a formatter bug.)
Running "appletviewer Hello.html" will show you the applet. One
advantage of using the appletviewer is that events sent to the applet
(start(), init(), etc) are in compliance with Sun specs as opposed to
Netscape 2.0b4 (probably a bug in Netscape).
A disadvantage of using the appletviewer is that it is much more
slower than Netscape.
The first time you run Java, a license screen resembling Netscape's
will be displayed.
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Notes on Known Problems
***********************
* Menu:
* GNU Make breaks after I install Java::
* You get `dirname: too many arguments' errors::
* You get `cannot find class java/lang/Thread' errors::
* An error message refers to /dev/zero::
* SEGFAULT::
* bin/java bin/javac or bin/appletviewer gives you a help screen::
* Applets show in the viewer but not when put on a web server::
* Problem Logging::
File: java-linux-HOWTO.2.0.info, Node: GNU Make breaks after I install Java, Next: too many arguments' errors:, Up: Notes on Known Problems
GNU Make breaks after I install Java
====================================
Recent versions of libc fix a bug which masked a bug in GNU Make (the
symptom is that make doesn't look in Makefile for rules). The libc
5.2.8 release notes give a patch to make that fixes the problem.
File: java-linux-HOWTO.2.0.info, Node: You get `dirname: too many arguments' errors
You get `dirname: too many arguments' errors
============================================
Your CLASSPATH variable is not correctly initialized. In
.java_wrapper, there is code akin to the follwing:
PRG=`which $0`
J_HOME=`dirname $PRG`/..
Unfortunately, linux's standalone which command is hideously broken,
and certain shells will set $0 to the full pathname. Randy Chapman
says the fix is either to use:
J_HOME=`dirname $0`/..
Or, safer:
J_HOME=/usr/local/java
An alternate fix from Dave Dittrich is:
PRG=`csh -c "which $0"`
And another one from Tim Farnum is to change the PRG=`which $0` line
to
PRG=$0
Lutz Behnke suggests:
PRG=`type -path $0` >/dev/null 2>&1
A similar change also needs to be made to the appletviewer script.
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You get `cannot find class java/lang/Thread' errors
Your CLASSPATH variable is not correctly initialized. See above.
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An error message refers to /dev/zero
====================================
Go root and do `chmod 666 /dev/zero'.
File: java-linux-HOWTO.2.0.info, Node: SEGFAULT, Next: bin/java bin/javac or bin/appletviewer gives you a help screen, Prev: An error message refers to /dev/zero, Up: Notes on Known Problems
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.
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bin/java bin/javac or bin/appletviewer gives you a help screen
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Applets show in the viewer but not when put on a web server
