Wednesday, April

How To Troubleshoot Common HTTP Error Codes

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When being able to view an online server or application, every HTTP ask that’s received having a server is taken proper care of immediately by getting an HTTP status code. HTTP status codes are three-digit codes, and so are grouped into five different classes. The course from the status code might be identified by its first digit:

  • 1xx: Informational
  • 2xx: Success
  • 3xx: Redirection
  • 4xx: Client Error
  • 5xx: Server Error

The following information focuses on identifying and troubleshooting most likely probably the most generally experienced HTTP error codes, i.e. 4xx and 5xx status codes, in the system administrator’s perspective. There are numerous situations that can lead to a web server to resolve a request getting a specific error code – we’ll cover common potential causes and solutions.

Client and Server Error Overview

Client errors, or HTTP status codes from 400 to 499, come from HTTP demands sent having a user client (i.e. a web browser or other HTTP client). Even though these types of errors are client-related, it’s frequently useful to know which error code one is encountering to discover once the potential issue might be fixed by server configuration.

Server errors, or HTTP status codes from 500 to 599, are returned having a server when it is conscious of an error has happened or possibly is otherwise not able to process the request.

General Troubleshooting Tips

When working with a web browser to check on an online server, refresh the browser after making server changes

Check server logs to learn more about how precisely the server is handling the requirements. For example, web servers for instance Apache or Nginx produce two files referred to as access.log and error.log which may be scanned for relevant information

Keep in mind that HTTP status code definitions are people of the that’s implemented with the application that’s serving demands. Meaning the specific status code that’s returned is determined by how a server software handles a particular error – the following information should generally point you inside the right direction

Now that you’ve a greater-level understanding of HTTP status codes, we’ll think about the generally experienced errors.

400 Bad Request

  • The 400 status code, or Bad Request error, means the HTTP ask which was sent to the server has invalid syntax.
  • Right here are a handful of kinds of each time a 400 Bad Request error might occur:
  • The user’s cookie that’s connected while using web site is corrupt. Clearing the browser’s cache and cookies could solve this issue
  • Deformed request because of faulty browser
  • Deformed request due to human error when by hands developing HTTP demands (e.g. using curl incorrectly)

401 Unauthorized

The 401 status code, or possibly an Unauthorized error, signifies that the customer attempting to connect with the resource isn’t authenticated or perhaps is not authenticated correctly. Meaning the customer must provide credentials to be able to begin to see the protected resource.

An example scenario where a 401 Unauthorized error might be returned is when an individual tries to access an origin that’s compensated by HTTP authentication, just like this Nginx tutorial. In this particular situation, the customer will receive a 401 response code until they provide the best password (the one that exists inside the .htpasswd file) towards the internet server.

403 Forbidden

The 403 status code, or possibly a Forbidden error, signifies that the customer developed a valid request nevertheless the server is refusing for everybody the request, because of inadequate permission to get into the requested resource. If you are encountering a 403 error all of a sudden, there’s a few typical causes that are described here.

File Permissions

403 errors generally occur when the user that’s running the internet server process does not have adequate permissions to determine the file that’s being utilized.

To supply among troubleshooting a 403 error, assume the following situation:

The customer is wanting to get into the internet server’s index file, from

The internet server worker process is part of the internet-data user

Round the server, the index file can be found at /usr/share/nginx/html/index.html

Once the user will get a 403 Forbidden error, make certain that internet-data user has sufficient permissions to determine the file. Typically, meaning another permissions in the file needs to be set to determine. There are lots of techniques to ensure this, nevertheless the following command works in this particular situation:

sudo chmod o=r /usr/share/nginx/html/index.html


Another potential reason behind 403 errors, frequently intentionally, is applying an .htaccess file. The .htaccess file enables you to deny access of certain sources to particular IP addresses or ranges, for example.

Once the user is all of a sudden acquiring a 403 Forbidden error, make sure that it isn’t introduced on from your .htaccess settings.

Index File Does not Exist

Once the user is wanting to get into a directory with no default index file, and directory listings aren’t enabled, the internet server will return a 403 Forbidden error. For example, once the user is wanting to get into, and there isn’t any index file inside the emptydir directory round the server, a 403 status will probably be returned.

If you’d like directory listings to get enabled, you may accomplish this within your server configuration.

404 Not Found

The 404 status code, or possibly a Not Found error, signifies that the customer has the ability to speak with the server but it is unable to uncover the requested file or resource.

404 errors can occur in a large number of situations. Once the user is all of a sudden obtaining a 404 Not Found error, listed here are a couple of things to ask while troubleshooting:

Will the hyperlink that directed the customer for the server resource have a very typographical error within it?

Did the customer type in the wrong URL?

Will the file come in the best location round the server? Was the resource was moved or deleted round the server?

Will the server configuration hold the correct document root location?

Will the consumer that owns the internet server worker process have legal rights to traverse for the directory the requested file is at? (Hint: directories require read and execute permissions to get utilized)

Could be the resource being utilized a symbolic link? If that is the situation, make certain the server is configured to check out symbolic links

500 Internal Server Error

The 500 status code, or Internal Server Error, signifies that server cannot process the request a mysterious reason. Sometimes this code look when more specific 5xx errors tend to be appropriate.

This most frequent reason behind this error is server misconfiguration (e.g. a deformed .htaccess file) or missing packages (e.g. trying to do a PHP file without PHP installed properly).

502 Bad Gateway

The 502 status code, or Bad Gateway error, signifies that the server can be a gateway or proxy server, which would be to not obtain a legitimate response within the backend servers that ought to really match the request.

Once the server into consideration can be a reverse proxy server, just like a load balancer, right here are a handful of products to check on:

The backend servers (where the HTTP demands are increasingly being provided to) are healthy

Overturn proxy is configured properly, while using proper backends specified

The network outcomes of the backend servers and reverse proxy server is nice. Once the servers can communicate on other ports, ensure the firewall is allowing the traffic together

In situation your internet application is configured to concentrate around the socket, make certain that socket exists inside the correct location which gets the proper permissions

503 Service Unavailable

The 503 status code, or Service Unavailable error, signifies that the server is overloaded or under maintenance. This error ensures that the service should become available eventually.

Once the server is not under maintenance, this might indicate the server does not have sufficient CPU or memory sources to cope with all of the incoming demands, or even the server should be configured allowing more users, threads, or processes.

504 Gateway Timeout

The 504 status code, or Gateway Timeout error, signifies that the server can be a gateway or proxy server, which would be to not have your call answered within the backend servers within the allowed time period.

This typically happens within the next situations:

The network outcomes of the servers is poor

The backend server that’s fulfilling the request is just too slow, due to poor performance

The gateway or proxy server’s timeout duration is just too short


You now understand the most frequent HTTP error codes, and customary techniques to individuals codes, you need to have an excellent cause for troubleshooting problems with your online servers or applications.

In the event you encounter any error codes that have been not stated in this particular guide, or else you recognize other likely techniques to individuals which were described, you are able to discuss them inside the comments.

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