# Homebrew: Error: Permission denied @ dir_s_mkdir - /usr/local/Cellar / /opt/homebrew is not writable

**Code:** `Homebrew: Permission denied @ dir_s_mkdir` · **Category:** macOS · **Seen on:** macOS

Homebrew can't write to its prefix because the folders are owned by another user or root.

## Meaning

Homebrew should be owned by your user. Fix ownership with `sudo chown -R $(whoami) $(brew --prefix)/*` (Intel: /usr/local; Apple Silicon: /opt/homebrew), and make sure you never run `sudo brew`. `brew doctor` lists the exact problems.

## Common causes

- Installed with sudo or by another user
- Ownership changed by migration/restore
- Mixed Intel/ARM Homebrew prefixes
- Running brew as root
- Folder missing (/usr/local/share/man)

## Quick fix

1. `sudo chown -R $(whoami) $(brew --prefix)/*`
2. `brew doctor` and fix what it reports
3. Never use `sudo brew`

## Detailed fix by platform

### macOS

1. `brew --prefix && ls -ld $(brew --prefix) && brew doctor`

## How to diagnose

1. **Prefix** — /opt/homebrew or /usr/local?
2. **Owner** — You?
3. **Sudo** — Used before?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/macos/brew-permission-denied-prefix)