How to Use the arch Command in macOS Terminal to Run Binaries Under Rosetta 2 or Native Apple Silicon

Apple Silicon Macs (M1, M2, M3, and M4 series) utilize the 64-bit ARM architecture (arm64). While modern macOS software is compiled natively for Apple Silicon, developers frequently encounter legacy CLI tools, Python C-extensions, or containerized binaries compiled exclusively for Intel x86_64 processors. Through Apple’s Rosetta 2 translation layer and the built-in arch command-line utility, you can selectively invoke binaries or spawn entire shell environments under x86_64 emulation or native arm64 execution on demand.

Understanding Universal Binaries and Architecture Translation

Universal 2 binaries contain distinct compiled slices for both arm64 and x86_64 within a single Mach-O file. By default, macOS automatically selects the native arm64 slice on Apple Silicon hardware. However, when compiling software against legacy dependencies that lack ARM support, you must force the system to invoke the x86_64 slice through Rosetta 2. The arch utility changes the target architecture before passing execution to the target binary.

Syntax and Key Options

arch -arch_name command [arguments]

• -arm64: Forces execution using the native 64-bit ARM slice.
• -arm64e: Runs with pointer authentication code (PAC) support enabled.
• -x86_64: Forces execution through Rosetta 2 Intel emulation.
• -x86_64h: Runs the Haswell-optimised 64-bit Intel architecture slice.

Step-by-Step Practical Implementation

Step 1: Check Your Current Shell Architecture

1. Open Terminal from /Applications/Utilities/.
2. Run the uname -m command:

   uname -m

3. On Apple Silicon, this returns arm64. If running under Rosetta emulation, it returns x86_64.

Step 2: Inspect Binary Architecture Slices

Before forcing an architecture, verify which slices exist inside a Mach-O executable using file or lipo:

file /usr/bin/uname

Output demonstrates a universal executable:

/usr/bin/uname: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64e:Mach-O 64-bit executable arm64e]

Step 3: Run an Individual Command Under Rosetta 2

To run a command under x86_64 emulation without altering your global shell configuration, prefix it with arch -x86_64:

arch -x86_64 uname -m

Terminal executes through Rosetta 2 and outputs: x86_64.

Step 4: Launch an Emulated x86_64 Subshell

If you are building an extensive project with multiple legacy npm or Python dependencies, running every command with a prefix is tedious. Launch an interactive Zsh subshell entirely under Rosetta:

arch -x86_64 zsh

Any subcommands, compilers, or build scripts run inside this session will execute within the x86_64 runtime environment automatically.

To return to your native Apple Silicon shell, simply enter:

exit

Step 5: Managing Dual Homebrew Environments

Apple Silicon systems typically maintain two separate Homebrew installations: native ARM at /opt/homebrew and Rosetta Intel at /usr/local. To install Intel-only packages, invoke the x86_64 Homebrew binary:

arch -x86_64 /usr/local/bin/brew install legacy-package

Architecture Comparison on Apple Silicon

Execution Mode	Architecture Flag	Translation Engine	Performance Profile	Primary Use Case
Native Apple Silicon	-arm64	Direct Silicon Execution	Maximum throughput and efficiency	Everyday development, production builds, and native CLI tools
Rosetta 2 Emulation	-x86_64	Apple Rosetta 2 JIT / AOT	~70-85% native performance	Compiling unported C-extensions and running legacy x86 CLIs
Pointer Authentication	-arm64e	Hardware PAC on Apple Silicon	Native with enhanced kernel security	Security research and system daemon debugging

Troubleshooting Common Errors

• “Bad CPU type in executable”: Rosetta 2 is not installed on your Mac. Install it via Terminal with softwareupdate --install-rosetta --agree-to-license.
• Architecture Mismatch in Compilers: Attempting to link an x86_64 static library against an arm64 binary generates an ld: symbol(s) not found for architecture arm64 error. Ensure all dependencies are built using the matching arch -x86_64 environment.