Resolving the `r - f951: internal compiler error: Illegal instruction: 4` Issue in R with macOS Systems

Introduction

The r - f951: internal compiler error: Illegal instruction: 4 error is a known issue in R, particularly when compiling packages on macOS systems. In this article, we’ll delve into the details of this error and explore possible solutions to resolve it.

Understanding the Error

When an internal compiler error occurs, it’s usually due to a problem with the compiler itself or a compatibility issue between the package being compiled and the operating system. The Illegal instruction: 4 message specifically indicates that the gfortran compiler encountered an instruction it couldn’t execute.

In this case, the error is triggered by the rrcov package, which uses Fortran for its functionality. The exact cause of the issue might be related to a specific version or configuration of the gfortran compiler.

Background: Compiling Packages in R

When you install a new package in R, it’s often compiled from source code using a C++ frontend (like R CMD BUILD). However, some packages rely on Fortran, which is compiled separately using a different set of tools. In this case, the rrcov package uses gfortran for its Fortran compilation.

The compilation process involves several steps:

Compilation: The Fortran source code is compiled into object files.
Linking: The object files are linked together to form an executable file.
Installation: The resulting executable is copied to the installation directory.

Troubleshooting

1. Install XCode and Reinstall R

Installing XCode can sometimes resolve issues related to gfortran. You should make sure that you have installed XCode, then reinstall R.

However, in this specific case, even after reinstalling R, we still encountered the issue with rrcov.

2. Verify Fortran Installation

We need to ensure that our system has a functional Fortran compiler and installation directories are correct.

Let’s verify the gfortran installation:

## Verifying Fortran Installation
> install --upgrade gfortran

If you encounter any errors while installing or upgrading, try removing it using:

## Uninstalling gfortran
> sudo rm -rf /Library/Developer/Compiler/gfortran
> sudo rm -rf /usr/bin/gfortran
> sudo rm -rf /usr/libexec/gfortran

And then reinstall the latest version of gfortran.

3. Check for Compatibility Issues

There might be a compatibility issue with your macOS system or the rrcov package. You can try to:

## Checking Package Version
> install.packages("rrcov")
> pkgdown::pkgdown_version("rrcov")

If you encounter any errors while checking the version, it may indicate an incompatibility.

4. Consider Alternative Packages

As a workaround, if you only need to perform multivariate analysis, consider using alternative packages that don’t rely on Fortran compilation.

Some examples include:

mvtna: A package for multivariate normal analysis.
sem: A package for structural equation modeling.

Additional Resources and Advice

For further assistance, refer to:

The official R documentation: https://cran.r-project.org/bin/macosx/R-3.5.0/index.html
Stack Overflow threads related to the issue: https://stackoverflow.com/questions/tagged/r-f951
Package documentation for rrcov: https://crantion.org/packages/rrcov

If you’re still encountering issues, consider:

Searching online forums or Reddit communities dedicated to R and macOS.
Posting on Stack Overflow with the specific error message and system configuration.

By following these steps and troubleshooting tips, we should be able to resolve the f951: internal compiler error: Illegal instruction: 4 issue in rrcov.

Last modified on 2025-04-25