Building Ruby

Quick start guide

  1. Install the prerequisite dependencies for building the CRuby interpreter:

    • C compiler

    • autoconf - 2.67 or later

    • bison - 3.0 or later

    • gperf - 3.0.3 or later

    • ruby - 2.7 or later

  2. Install optional, recommended dependencies:

    • OpenSSL/LibreSSL

    • readline/editline (libedit)

    • zlib

    • libffi

    • libyaml

    • libexecinfo (FreeBSD)

    • rustc - 1.58.0 or later (if you wish to build YJIT)

  3. Checkout the CRuby source code:

    git clone
  4. Generate the configure file:

  5. Create a build directory outside of the source directory:

    mkdir build && cd build

    While it's not necessary to build in a separate directory, it's good practice to do so.

  6. We'll install Ruby in ~/.rubies/ruby-master, so create the directory:

    mkdir ~/.rubies
  7. Run configure:

    ../configure --prefix="${HOME}/.rubies/ruby-master"
    • If you are frequently building Ruby, add the --disable-install-doc flag to not build documentation which will speed up the build process.

  8. Build Ruby:

    make install
    • If you're on macOS and installed OpenSSL through Homebrew, you may encounter failure to build OpenSSL that look like this:

          Could not be configured. It will not be installed.
          ruby/ext/openssl/extconf.rb: OpenSSL library could not be found. You might want to use --with-openssl-dir=<dir> option to specify the prefix where OpenSSL is installed.
          Check ext/openssl/mkmf.log for more details.

      Adding --with-openssl-dir=$(brew --prefix openssl) to the list of options passed to configure may solve the issue.

      Remember to delete your build directory and start again from the configure step.

  9. Run tests to confirm your build succeeded.

Unexplainable Build Errors

If you are having unexplainable build errors, after saving all your work, try running git clean -xfd in the source root to remove all git ignored local files. If you are working from a source directory that's been updated several times, you may have temporary build artifacts from previous releases which can cause build failures.

More details

If you're interested in continuing development on Ruby, here are more details about Ruby's build to help out.

Running make scripts in parallel

In GNU make and BSD make implementations, to run a specific make script in parallel, pass the flag -j<number of processes>. For instance, to run tests on 8 processes, use:

make test-all -j8

We can also set MAKEFLAGS to run all make commands in parallel.

Having the right --jobs flag will ensure all processors are utilized when building software projects. To do this effectively, you can set MAKEFLAGS in your shell configuration/profile:

# On macOS with Fish shell:
export MAKEFLAGS="--jobs "(sysctl -n hw.ncpu)

# On macOS with Bash/ZSH shell:
export MAKEFLAGS="--jobs $(sysctl -n hw.ncpu)"

# On Linux with Fish shell:
export MAKEFLAGS="--jobs "(nproc)

# On Linux with Bash/ZSH shell:
export MAKEFLAGS="--jobs $(nproc)"

Miniruby vs Ruby

Miniruby is a version of Ruby which has no external dependencies and lacks certain features. It can be useful in Ruby development because it allows for faster build times. Miniruby is built before Ruby. A functional Miniruby is required to build Ruby. To build Miniruby:

make miniruby


You can use either lldb or gdb for debugging. Before debugging, you need to create a test.rb with the Ruby script you’d like to run. You can use the following make targets:

Building with Address Sanitizer

Using the address sanitizer is a great way to detect memory issues.

mkdir build && cd build
export ASAN_OPTIONS="halt_on_error=0:use_sigaltstack=0:detect_leaks=0"
../configure cppflags="-fsanitize=address -fno-omit-frame-pointer" optflags=-O0 LDFLAGS="-fsanitize=address -fno-omit-frame-pointer"

On Linux it is important to specify -O0 when debugging. This is especially true for ASAN which sometimes works incorrectly at higher optimisation levels.

How to measure coverage of C and Ruby code

You need to be able to use gcc (gcov) and lcov visualizer.

./configure --enable-gcov
make update-coverage
rm -f test-coverage.dat
make test-all COVERAGE=true
make lcov
open lcov-out/index.html

If you need only C code coverage, you can remove COVERAGE=true from the above process. You can also use gcov command directly to get per-file coverage.

If you need only Ruby code coverage, you can remove --enable-gcov. Note that test-coverage.dat accumulates all runs of make test-all. Make sure that you remove the file if you want to measure one test run.

You can see the coverage result of CI: