next.js/errors/build-dir-not-writeable.mdx

---
title: Handling "Build Directory Not Writeable" Error in Next.js
description: This document explains the "Build Directory Not Writeable" error in Next.js and provides a solution to resolve this issue.
---

## 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](/docs/pages/guides/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:

```json filename="package.json"
{
  "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`:

```js filename="server.js"
const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev })
```

## Useful Links

- [Custom Server documentation + examples](/docs/pages/guides/custom-server) - Learn more about how to effectively set up and manage an ejected server in Next.js.