JRuby may start slower than expected versus the C-based Ruby implementation (MRI). Fortunately, JRuby offers flags that can improve the start time and tune applications. Several Java flags can also be used in conjunction with or apart from the JRuby flags in order to improve the start time even more.

For small tasks such as converting an AsciiDoc document, two JRuby flags can drastically improve the start time:

JRuby flags
Name Value





When using AsciidoctorJ via the API these flags have to be set as system properties when creating the org.asciidoctor.Asciidoctor instance:

System.setProperty("jruby.compat.version", "RUBY1_9");
System.setProperty("jruby.compile.mode", "OFF");
Asciidoctor asciidoctor = Asciidoctor.Factory.create();

When starting AsciidoctorJ via the CLI these options can be defined in the files .jrubyrc that are loaded from the current working directory and the home directory of the user.

$ cat ./.jrubyrc
$ ./asciidoctorj -V
AsciidoctorJ 1.5.2 [https://asciidoctor.org]
Runtime Environment: jruby 1.7.20 (1.9.3)
The properties in these .jrubyrc files do not contain the prefix jruby.. The property values also must not have trailing blanks!

Alternatively you can also set any system properties using the environment variable ASCIIDOCTORJ_OPTS:

$ export ASCIIDOCTORJ_OPTS=-Djruby.compat.version=RUBY1_9
$ asciidoctorj -V
AsciidoctorJ 1.5.2 [https://asciidoctor.org]
Runtime Environment: jruby 1.7.20 (1.9.3)

The Java flags available for improving start time depend on whether your working on a 32- or 64-bit processor and your JDK version. Let’s see a summary of these flags and in which environments they can be used.

Java flags
Name JDK


32 bit Java


32/64 bit Java


32/64 bit Java SE 7


32/64 bit Java SE 7

Setting flags for Java SE 6
export JAVA_OPTS="-Xverify:none -client"