OpenJDK
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[[wikipedia::OpenJDK|OpenJDK]] is a version of [[JDK]] released under [[GPL]] (with [[GNU Classpath]] exception) [[open source]] license. [[OpenJDK]] comes with various ''improvements'' over the classical [[Oracle]]'s [[JDK]] which often makes the [[OpenJDK]] much less usable than the original. One of the problems is the modified launcher parameters as described in [[Virtualization]] page. Instead of being helpful, it just makes the whole system unusable. However, at least the system starts. | [[wikipedia::OpenJDK|OpenJDK]] is a version of [[JDK]] released under [[GPL]] (with [[GNU Classpath]] exception) [[open source]] license. [[OpenJDK]] comes with various ''improvements'' over the classical [[Oracle]]'s [[JDK]] which often makes the [[OpenJDK]] much less usable than the original. One of the problems is the modified launcher parameters as described in [[Virtualization]] page. Instead of being helpful, it just makes the whole system unusable. However, at least the system starts. | ||
| - | For a while I've been struggling with [[Java]] on my hosted [[Linux]] ( | + | For a while I've been struggling with [[Java]] on my hosted [[Linux]] (running [[CentOS]]). Whenever I tried: |
<source lang="bash"> | <source lang="bash"> | ||
| Line 19: | Line 19: | ||
(to execute a jar file) | (to execute a jar file) | ||
</source> | </source> | ||
| + | |||
| + | ==== Global Configuration ==== | ||
The question however is: How to modify each [[JDK]] utility ('''jar''', '''javac''', '''javadoc''', etc.) to use this changed setting? Usual [[Unix]] style is to locate ''/etc/java.conf'' and tweak it. But of course [[Java]] has multiplatform, not [[Unix]] roots, so no such configuration file exists, as far as I can tell. I thought configuring the default options for all [[Java]] processes is impossible. However today I realized that | The question however is: How to modify each [[JDK]] utility ('''jar''', '''javac''', '''javadoc''', etc.) to use this changed setting? Usual [[Unix]] style is to locate ''/etc/java.conf'' and tweak it. But of course [[Java]] has multiplatform, not [[Unix]] roots, so no such configuration file exists, as far as I can tell. I thought configuring the default options for all [[Java]] processes is impossible. However today I realized that | ||
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==== Jan 30, 2014 update ==== | ==== Jan 30, 2014 update ==== | ||
| - | + | I've run into the same problem again after switching to new [[CentOS]] 6. This time it is amd64 bit [[Virtualization|virtualized]] environment and to make things worse, the 64-bit [[Java]] does not have the ''client'' mode anymore! | |
| + | |||
| + | After a lot of work and reading through sources we found out there is an [[environment]] variable that [[Java]] honors: | ||
| + | |||
| + | Well, it is not documented, but there is: | ||
| + | |||
| + | <source lang="bash"> | ||
| + | _JAVA_OPTIONS="-Xmx64M -XX:MaxPermSize=32M" | ||
| + | export _JAVA_OPTIONS | ||
| + | </source> | ||
| + | |||
| + | Still I wonder. Am I really the only person on a planet to run into such issues? | ||
Current revision
OpenJDK is a version of JDK released under GPL (with GNU Classpath exception) open source license. OpenJDK comes with various improvements over the classical Oracle's JDK which often makes the OpenJDK much less usable than the original. One of the problems is the modified launcher parameters as described in Virtualization page. Instead of being helpful, it just makes the whole system unusable. However, at least the system starts.
For a while I've been struggling with Java on my hosted Linux (running CentOS). Whenever I tried:
$ java
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.Why? The system has a lot of resources, so where is the problem? It turned out that the workaround is easy. Just to limit the number of available memory (this by itself is ridiculous, but it shows that allowing virtualization is not the primary driver for evolution of Java technology):
$ java -mx64M Usage: java [-options] class [args...] (to execute a class) or java [-options] -jar jarfile [args...] (to execute a jar file)
Global Configuration
The question however is: How to modify each JDK utility (jar, javac, javadoc, etc.) to use this changed setting? Usual Unix style is to locate /etc/java.conf and tweak it. But of course Java has multiplatform, not Unix roots, so no such configuration file exists, as far as I can tell. I thought configuring the default options for all Java processes is impossible. However today I realized that
$ java -client
works too fine as well. From that moment it was just a small step to symlink the server directory inside the JDK installation to client:
$ cd jre/lib/i386/ $ mv server/ server.bak/ $ ln -s client server
Now I can use all the JDK functionality without problems. However it took me a while to get there. No surprise nobody offers Java in virtualized environments, when it is so hard to set it up (and PHP is instantly ready).
Btw. this shows that location of your files on disk is an important type of API which can compensate missing presence of a configuration file.
Jan 30, 2014 update
I've run into the same problem again after switching to new CentOS 6. This time it is amd64 bit virtualized environment and to make things worse, the 64-bit Java does not have the client mode anymore!
After a lot of work and reading through sources we found out there is an environment variable that Java honors:
Well, it is not documented, but there is:
_JAVA_OPTIONS="-Xmx64M -XX:MaxPermSize=32M" export _JAVA_OPTIONS
Still I wonder. Am I really the only person on a planet to run into such issues?
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