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JRuby Java Options Files

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Charles Oliver Nutter edited this page Oct 30, 2019 · 1 revision

JRuby allows passing JVM options at the command line using the -J<javaoption> flag. Because these options may be quite verbose, may differ between applications and environments, and may encode important configuration details for a given app, we now support (in JRuby 9.2.9 and higher) a .jruby.java_opts file.

Command-line Argument Files

Java 9 introduced support for command-line argument files, which allows you to aggregate JVM options in a file and include those options on the command line with the syntax @<filename> rather than passing them directly. JRuby builds on this feature and supports it on Java 8 via our .jruby.java_opts files.

.jruby.java_opts

The format of .jruby.java_opts is as documented in the Java documentation above, with options separated by whitespace (spaces, tabs, newlines, etc) or enclosed in quotes to preserve spaces.

On startup, JRuby will look for .jruby.java_opts files in the following locations:

  1. In the installed JRuby's bin/.jruby.java_opts (empty by default).
  2. In the current user's home directory at ~/.jruby.java_opts.
  3. In the current working directory at ./.jruby.java_opts.

Options passed through JRuby to the JVM via different mechanisms will override each other. Given options are processed in the following order, with later options overriding earlier ones:

  1. Any .jruby.java_opts files will be processed in the order shown above.
  2. The JAVA_OPTS environment variable will be processed.
  3. Any flags passed at JRuby's command line using -J<option> will be processed last.

An example file, used by JRuby's --dev flag, can be found in the JRuby install under bin/.dev_mode.java_opts.

In order to help users understand where options are coming from, and to inspect the eventual set of JRuby and Java options being used, we added in 9.2.10 the --environment flag. See Environment Flag for more information.

Notes

  • Argument files are only directly supported by the java launcher in Java 9 and higher, but JRuby also supports using .jruby.java_opts on Java 8. Because we do this by expanding the file's contents directly into our final java command, it's possible for this argument list to exceed some shells' character limit.
  • There's no way at present to separate .jruby.java_opts files by Java version or JVM implementation, mostly due to the difficulty of detecting what JVM you are using before startup. We are exploring other options here.
  • JRuby also support passing JRuby options via .jrubyrc files from the user's home or from the current directory. See Configuring JRuby for more information on .jrubyrc files.
  • A separate options file, in bin/.jruby.module_opts, is used when running on a Java Module-enabled JVM. By default it opens packages that JRuby needs for Ruby compatibility.
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