In linux/unix enviroment, Apache is the most widely used web server on dedicated or cloud servers.

Here are few common errors one might get and what they could mean:

301 Moved Permanently
This error tells the web browser that the content has been moved to a new location and it should the agent its new location and use that location in the future.

400 Bad Request
This is basically telling you the application or web browser you are using accessed it incorrectly. If few users are reporting this problem it could be on the user side. While on the other hand if multiple user recieve the error, it could be a problem with the config, or web server.

401 HTTP error
This error occurs when a user tries to access restricted part of the site when they don’t suppose to have access to it. IE Bad username and/or pasword

403 Forbidden
This is telling you the user trying to access the site either entered the wrong username and password, intentionally trying to gain access to a site that off limit to the user.

If the user does have permission to view the content on the website and receive this error, you would have to change the permission on the content.

404 Not Found
This basically means that the file never existed, no longer there, or could be placed in the wrong location.

408 Request Timeout
As the name describe. The server did not respond to the user request in time. Occasional timeout are normal, but if it happens frequently it could mean you may need to check the network or the server load.

500 Internal Server Error
The error is a general error message, which could relate to number of things.