your own template for a [custom 404 error page](https://help.github.com/articles/custom-404-pages/) by creating a 404.html template file in your `/layouts` folder. When Hugo generates your site, the `404.html` file will be placed in the root.
Your 404.html file can be set to load automatically when a visitor enters a mistaken URL path, dependent upon the web serving environment you are using. For example:
* _Github Pages_ - it's automatic.
* _Apache_ - one way is to specify `ErrorDocument 404 /404.html` in an `.htaccess` file in the root of your site.
* _Nginx_ - you might specify `error_page 404 = /404.html;` in your `nginx.conf` file.
* _Amazon AWS S3_ - when setting a bucket up for static web serving, you can specify the error file.