After fielding requests from users who wanted a straightforward way to get OpenMP working on macOS without additional R or R package dependencies using the main Xcode CLI toolchain, I put together OpenMP Setup, Uninstall, and Check Tools: a collection of shell scripts that handle the entire workflow.
Apple hates OpenMP
Getting OpenMP running on macOS has always been a bit of a puzzle since Apple purposely omits it from its Xcode toolchain by default. This is despite widespread adoption of OpenMP on Windows and Linux. Thus, when we compile a C/C++ script necessitating OpenMP on macOS we get hit with:
clang: error: unsupported option '-fopenmp'
fatal error: 'omp.h' file not foundSolutions, there’s been a few
Over the years, a couple solutions have emerged to address this gap. They mainly rely upon Homebrew and MacPorts to install and manage a separate toolchain outside of Apple’s ecosystem. That is, for Homebrew, you need to first install llvm and libomp with:
brew install llvm
brew install libompThen, when compiling C/C++ code that uses OpenMP, you need to include the following flags:
-Xclang -fopenmp -lomp -L/opt/homebrew/opt/libomp/lib -I/opt/homebrew/opt/libomp/includeOr, simply:
-Xclang -fopenmp -lomp -L"$(brew --prefix libomp)/lib" -I"$(brew --prefix libomp)/include"Though, this can lead to conflicts with the default Apple Clang compiler which causes compatibility issues on pre-compiled binaries for popular R packages from CRAN or Bioconductor. Thus, requiring users to recompile packages from source via install.packages("pkg", type="source") which can be time-consuming and error-prone (as dependencies may also be need).
A Better Approach: Use Apple’s Toolchain
The good news is that we can use the libomp.dylib run-time library and associated headers for compilation that are available from the clang version embedded in the installed Xcode version. Thanks to the CRAN maintainer for macOS binaries the mapping between Xcode, Clang, and OpenMP is detailed on the R CRAN macOS tools page.
While the {macrtools} package provides a solution that directly implemented the logic alongside of an installation process inside of R of other toolchain components, some folks wanted to be able to set up OpenMP outside of R entirely, or just wanted a more lightweight approach without R package dependencies. Either to include the setup in administrative scripts, or to use OpenMP in other programming languages.
Overview of Scripts
The shell script collection provides three focused tools:
install-openmp.sh handles automatic Xcode version detection and downloads official CRAN binaries; check-openmp.sh performs diagnostics across five categories; and uninstall-openmp.sh provides safe removal with confirmation prompts and cleanup guidance.Usage
You can run the each script directly from the terminal using curl to download them on-the-fly. Make sure to give execute permissions with chmod +x before running.
Installation
For example, to install OpenMP, run:
# Install
curl -O https://github.com/coatless-shell/openmp/raw/main/install-openmp.sh
chmod +x install-openmp.sh && ./install-openmp.shThe installer handles the version mapping automatically (Xcode 16.3+ → OpenMP 19.1.0, Xcode 16.0-16.2 → OpenMP 17.0.6, etc.) and provides clear configuration instructions for three different approaches: global ~/.R/Makevars setup, per-session Sys.setenv(), or per-package flags.
/usr/local/lib and headers to /usr/local/include, and configuration guidance.Diagnostics
Once installed, you can verify everything is working with the diagnostic script:
# Check everything is working
curl -O https://github.com/coatless-shell/openmp/raw/main/check-openmp.sh
chmod +x check-openmp.sh && ./check-openmp.shThe checker runs a series of tests and provides clear feedback on what’s working and what isn’t, along with actionable next steps.
--disable-r flag for users focused solely on C/C++ compilation outside of R.Uninstallation
When you want to uninstall OpenMP, simply run:
# Uninstall
curl -O https://github.com/coatless-shell/openmp/raw/main/uninstall-openmp.sh
chmod +x uninstall-openmp.sh && ./uninstall-openmp.shThe uninstaller prompts for confirmation before removing files and offers guidance on cleaning up configuration files.
Maintenance Expectations
This project solves a specific, well-defined problem and is unlikely to see heavy updates. The core functionality is stable – it downloads official LLVM OpenMP builds from the R CRAN macOS OpenMP page and provides basic configuration verification.
Future updates would mainly involve:
- Adding support for new Xcode/OpenMP version combinations as they’re released
- Automatically configuring compilation variables for popular shells (e.g.,
.zshrc,.bashrc) and inside R’s~/.R/Makevars. - Bug fixes if installation edge cases emerge
Is This For You?
OpenMP Setup, Uninstall, and Check Tools is a viable alternative if you:
- Prefer shell scripts over R package solutions
- Need to set up OpenMP in non-R environments
- Want diagnostic tools that clearly explain what’s broken
- Like having explicit control over the installation process
If you’re already happy with {macrtools} or other solutions, there’s no compelling reason to switch. But if you’ve been looking for a lightweight, dependency-free approach to OpenMP on macOS, this might be exactly what you need.
See the code and further documentation on the GitHub repository.