Handling "Build Directory Not Writeable" Error in Next.js

Why This Error Occurred

The "Build Directory Not Writeable" error usually occurs when the file system does not permit writing to the designated directory. A common scenario for this error is when you initiate a custom server in development mode on a production server.

These production servers often disallow writing to the filesystem after your application is built, causing this error.

Possible Ways to Fix It

If you're deploying a custom server with a server file (let's assume it's named server.js), you should modify the scripts key in your package.json to the following:

{
  "scripts": {
    "dev": "node server.js",
    "build": "next build",
    "start": "NODE_ENV=production node server.js"
  }
}

Ensure that your custom server starts Next.js in production mode when NODE_ENV is set to production:

const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev })

Useful Links

• Custom Server documentation + examples - Learn more about how to effectively set up and manage an ejected server in Next.js.