404 and other common error codes when accessing web resources: how to understand and fix them

HTTP status codes: why they are needed and how to view them

The HTTP status code is a three-digit number that begins any server response to an HTTP request. This is how the server reports either the fact that the request has been fulfilled or that an error has occurred.

HTTP response codes are divided into five classes, each of which is designed for specific situations:

• 1хх — informational codes (reporting the progress of the request);
• 2хх — successful request codes (report that everything is working as it should);
• 3хх — codes of redirects (inform about moving the requested page and the need to perform another request to a new URL);
• 4хх — client error codes (report an error on the side of the user who sent the request);
• 5хх — server error codes (report an error on the side of the server that processed the request).

To see server response codes in popular browsers, you need to press the key combination:

• Ctrl + Shift + I — on a Windows or Linux computer;
• ⌘ + ⌥ + I — on a macOS computer.

Below we will consider the most common types of client (4xx) and server (5xx) errors, their causes and ways to fix them.

Most common client error codes (4xx)

All errors that start with 4 indicate that the problem is on the user's side.

400: Bad Request

HTTP 400 means that the server hosting the site cannot fully understand and correctly process the request sent to it by the user's browser. This type of error can occur if the request is garbled, incorrect, corrupted or damaged. But most often the reason is that the user used the URL of a non-existent website.

The causes of error 400 can be:

• an incorrect link to the page;
• use of outdated cookies;
• user uploading a too large file to the site;
• antivirus or firewall blocking the site;
• a virus on the computer that blocks access to the site;
• problems on the side of the Internet provider.

To fix error 400, you can use the following methods:

1. Refresh the page.
   

   In most browsers, you can do this by pressing the F5 key. Resending a request that may have been corrupted may also help.

2. Check the URL.
   

   If the error was caused by an incorrect URL entered by the user in the address bar, simply review and correct the address if necessary.

   If there was a typo in the link, the site will usually give a 404 error. Therefore, it is worth checking the correct spelling of the URL. If the link was copied from the site, try searching for the correct page using keywords. After entering the corrected address, the site will work.

3. Search for the page on the site.
   

   Incorrect address may be specified directly in the link to the web page. If such a page does exist, you can try to access it through the search bar by entering parts of the full address of the page.

4. Clear cookies and browser cache.
   

   If the cookies on the user's PC are corrupted or badly out of date, or if the browser has cached a corrupted web page that you are trying to open, clearing the cache data and cookies in a timely manner may help. You can do this not only manually, but also with special programmes (for example, CCleaner).

403: Forbidden

HTTP 403 means that the user is denied access to view the content of the site. This often happens due to:

• incorrectly set permissions for folders and files;
• an incorrectly set user/group for files and folders;
• prohibited access in the web server configuration file;
• site files uploaded to a folder other than the root folder on the hosting site;
• incorrectly specified index file name in the settings;
• an error caused by a plugin or extension.

In most cases, you will not be able to eliminate the problem of access denial by your own efforts. But there are a few options that you can try:

1. Refresh the web page.
   

   You can do this instantly in many popular browsers by pressing the F5 key.

2. Check the URL.
   

   Make sure that the URL in the search box is correct and actually points to the web page. If you find an error in the URL spelling, correct it.

3. Check your own permissions.
   

   Some sites restrict access to their content to specific categories of users (for example, registered users). So you may be one of those who simply don't have access.

404: Not Found

HTTP 404 means that the server could not find a page with this address. This error is the most common on the web and most often happens for the following reasons:

• deleting a page or moving it to another address, with the old link left somewhere;
• entering an address with an error (accidentally or on purpose to see the design of the 404 page);
• a failure in the template structure of permanent links.

If you have encountered a 404 error, you can try to fix it in several ways:

1. Refresh the problematic page.
   

   If the page pauses due to a failure, reloading the page by pressing the F5 key will help.

2. Verify that the URL is correct.
   

   If you make a mistake while typing a URL or the web page contains an incorrect link, enter the correct URL when you discover this.

3. Search for the correct page on the site.
   

   The URL you received may have been incorrect, or the wrong link may have been provided on the website you came from. If the page actually exists, try searching for it by name on the site's search bar.

Most common server error codes (5xx)

500: Internal Server Error

HTTP 500 means that the server encountered an unexpected error while processing the request, so it was unable to fulfil it.

The easiest way to find out the cause of error 500 is to look in the server logs. Some of the most common cases include:

• PHP script error;
• database problems;
• incorrect PHP parameters;
• incorrect access rights to folders and files;
• site conflict with a theme or plugin;
• CMS system file of the site is missing or corrupted;
• an error in the global configuration file of the web server;
• an error in the additional web server configuration file .htaccess;
• a link in one of the files to another file that is actually missing on the hosting;
• the script is not executed because the max_execution_time and memory_limit values are too low.

There are the following ways to fix error 500:

1. Refresh the reference page.
   

   Important warning! Don’t try to reload the web page if you tried to make an online payment or any type of money transfer before receiving the error message 500. After all, forcing the page to refresh may cause you to send one payment twice.

2. Access the resource later.
   

   Since server problems may be temporary, try to visit the web page after a short break.

3. Contact the site administration.
   

   If the problem persists, try contacting the website's support team and inform them of the problem.

502: Bad Gateway

HTTP 502 means that the server of the website you visited tried to retrieve some information from another server, but received an incorrect response. Among the possible causes:

• the server is overloaded or there was a network problem between the two servers;
• improper firewall settings or a coding error;
• problems on the user's PC or network hardware.

To fix the 502 error, you should try the following steps:

1. Refresh the page.
   

   After displaying the 502 error message, try quickly reloading the page by pressing the F5 key.

2. Check if the site is available to other users.
   

   To do this, visit a remote resource status checker site (IsItDownRightNow or DownforEveryoneorJustMe) and see if other users are having trouble accessing a particular resource, or if problems are only occurring locally on your device.

3. Access the website at a later date.
   

   A server problem may be temporary, so it's worth trying to access the site after a while.

4. Clear cookies and browser cache.
   

   If your web browser has cached outdated or corrupted files, performing a cache and cookie clearing procedure will help to fix this.

503: Service Unavailable

HTTP 503 means that the server is unavailable due to an overload or technical work being done on it. The cause of overload can be:

• DDoS attack;
• increased activity of a search robot;
• a large number of slow requests to the database;
• too heavy load of the server script.

It also happens that several situations cause error 503. To eliminate it, you need access to the hosting. Therefore, if you just went to someone else's site and saw the error code 503, while waiting for it to be fixed, you can try the following:

1. Refresh the problem page.
   

   In many popular web browsers you can do this by pressing the F5 key.

2. Check if the site is up and running.
   

   To do this, go to the remote resource status check site (IsItDownRightNow or DownforEveryoneorJustMe) and evaluate the availability of the resource for other users.

3. Go to the site later.
   

   A 503 error often occurs because the server is overloaded with requests and doesn’t have time to process all incoming messages. Try to visit the web page some time later.

It is important to understand the basic error codes when accessing web resources not only for website administrators, but also for ordinary users. Knowing how to correctly interpret problem messages and what actions to take to fix them will help ensure more stable and efficient access to online sites.