RESOLVED: ‘Configure: error: unexpected output of ‘arch’ on os’

When setting up software on macOS, you may encounter an error “Configure: error: unexpected output of ‘arch'”. it shows that the configure script, which is much needed for setting up the build environment to ensure successful compilation, has got an unexpected output from the ‘arch‘ command that it is unable to recognize correctly.

In computers, especially those made by Apple (like Macs), ‘arch‘ helps the computer understand what kind of instructions it should use to make sure the programs run correctly, The occurrence of this error indicates a mismatch between the expected and actual outputs produced by the ‘arch‘ command.

Resolving the “Configure: error: unexpected output of ‘arch’ on os” error involves understanding both the operating system’s architecture command and the configuration scripts that rely on its output to direct the compile process correctly.

Understanding the context ‘Configure: error: unexpected output of ‘arch’ on os’

Before proceeding to the resolution, it’s important to understand the context in which this error occurs. The configure script checks your system to ensure that all the necessary tools and libraries are available to compile the software.

“Configure: error” shows that the script encountered a failure that disturbed the build process. Specifically, “unexpected output of ‘arch’ on OSX” suggests that the utility meant to determine the processor architecture gave results the script did not expect. This may arise when building software on newer hardware, such as machines with Apple Silicon chips, that may not be fully supported by older scripts.

Role of ‘Arch’ in Builds

The arch command in macOS is a crucial tool that reports the active processor architecture (such as i386, x86_64, or arm64). It is vital in the build process because software often contains assembly code or optimizations specific to a processor’s architecture. If the arch command output deviates from what the configuration script anticipates, the build system may not be able to proceed and will halt, delivering the error message.

Prerequisites for Configuration

Before attempting to configure software on any system, it is important to ensure that the prerequisites are met. We can do this by checking system compatibility and verifying that all necessary dependencies are installed.

  1. Verify the Software Requirements: Ensure that your system meets the software requirements, including the correct version of compilers and libraries. Consult the README or INSTALL documentation of the software package for details.
  2. Update Your System: Ensure that your operating system and all its components are up-to-date. This can help avoid compatibility issues.
  3. Check arch Command Output: Run the arch command in your terminal and note its output. The configure script might expect a specific output format or value.
    • Command: Execute arch in the terminal.
    • Expected Outputi386 for Rosetta emulation, arm64 for Apple Silicon.

Real-time example:

When configuring Python environments, developers frequently encounter the configure: error: unexpected output of 'arch' message. This error is a common issue that primarily affects users trying to set up Python versions using Pyenv on newer Apple Silicon Macs or systems with specific architecture configurations.

Troubles with Pyenv Installation

Pyenv is a popular tool for managing multiple Python versions. Upon installation, Pyenv may struggle with readline or openssl dependencies, especially on Apple Silicon (M1) Macs.

We should ensure that readline and openssl are properly installed and recognized by Pyenv, which can be verified from the log files generated during the installation process.

Issues with Python Versions

Installing specific Python versions, such as Python 3.7.2 or 3.8.9, can occasionally result in errors due to architecture incompatibility. These versions may produce an ‘Unexpected output of ‘arch” error when the system architecture does not align with the Python build expectations.

Simulate the error (Just for understanding purposes)

We can easily replicate the error, By adding some random echo statement in your env PATH

Step1: create a file named arch with the following content:

cat arch

echo "Simulate the unexpected_arch error "

Step 2: Add the script’s directory to the start of your PATH variable. Open your shell profile file (.bash_profile, .zshrc, or another, depending on your shell) and add the following line at the end:

export PATH="$HOME/bin:$PATH"

Step3: Install python using pyenv

If you try to install Python, you encounter the arch the script, leading to a failure “configure: error: unexpected output of ‘arch

pyenv install <version>

Troubleshooting Steps

When encountering the ‘arch‘ error during installation on a macOS system, it often relates to issues with either the build tools or the environment configuration. Correcting such errors typically involves updating critical development tools or adjusting key environment variables.

Check Your Setup

  • Shell Compatibility: Check if your shell environment is compatible. certain scripts may not work well with some shells.
  • Environment Paths: Check your environment PATH variable is set up correctly, Make sure it includes the directories where crucial tools and compilers are located.

Investigate configure Script

  • Validate the Script: Check the configure script that uses the arch command. Understanding what output it expects can help us move forward.
  • Make changes in the Script: If you have identified what output the script expects and understand the discrepancy, consider modifying the script to accept the output of the arch on your system.

Note: This step requires caution and should be done with a backup of the original script.

System Architecture Verification

  • Ensure Supported Architecture: Check that the architecture of your system matches the requirements for the configure script. Incompatibilities with certain architectures can cause errors due to unexpected outputs.

Alternative Commands

  • Use uname -m: Some systems or shell environments might provide more reliable output with uname -m than arch. If the configure script allows, modify it to use uname -m for architecture detection.

Advanced Steps

If the above troubleshooting steps didn’t help to resolve the issue, consider these advanced steps:

  • Environment Emulation: For compatibility issues related to architecture, consider using an environment emulation tool or a virtual machine to create a virtual environment to check compatibility issues
  • Custom Build Options: Consider specifying custom options via arguments in the ./configure script that could circumvent the issue with the ‘arch’ command check.


I hope you have understood the context of the error “configure: error: unexpected output of ‘arch’ on OS” and the steps to troubleshoot and resolve the issue. Make sure you always make backups before modifying scripts or source code and consider reaching out to community support if you get stuck

Happy Learning!!

Jerry Richard
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