HTTP Status Codes You Must Know

2025-01-31

HTTP status codes are essential for web developers, IT professionals, and cybersecurity experts. They indicate the response status of an HTTP request between a client and a server. Here’s a breakdown of the most common HTTP status codes:

1xx – Informational

100 Continue – The server has received the request headers and expects the client to proceed.
101 Switching Protocols – The server is switching protocols as requested by the client.
102 Processing – The server has received and is processing the request but has not yet completed it.

2xx – Success

200 OK – The request was successful, and the server responded with the requested content.
201 Created – A new resource has been successfully created.
202 Accepted – The request has been accepted but is still being processed.
204 No Content – The request was successful, but there is no content to return.

3xx – Redirection

301 Moved Permanently – The requested resource has been permanently moved to a new URL.
302 Found – The requested resource is temporarily available at a different URL.
304 Not Modified – The requested resource has not changed since the last request.

4xx – Client Errors

400 Bad Request – The server could not understand the request due to invalid syntax.
401 Unauthorized – Authentication is required to access the requested resource.
403 Forbidden – The server refuses to authorize the request.
404 Not Found – The requested resource could not be found.
408 Request Timeout – The server timed out waiting for the request.

5xx – Server Errors

500 Internal Server Error – A generic server error occurred.
502 Bad Gateway – The server received an invalid response from an upstream server.
503 Service Unavailable – The server is temporarily unable to handle the request.
504 Gateway Timeout – The server did not receive a timely response from an upstream server.

What Undercode Say

Understanding HTTP status codes is crucial for troubleshooting web applications, improving security, and optimizing network performance. Here are some useful Linux commands to debug and analyze HTTP status codes:

Check HTTP Status of a URL

curl -I https://example.com

This command returns only the HTTP headers, including the status code.

Verbose cURL Request

curl -v https://example.com

This provides detailed information about the request and response.

Using wget to Check Response

wget --server-response --spider https://example.com

This command retrieves the headers without downloading the content.

Check Logs for Status Codes (Apache & Nginx)

For Apache:

tail -f /var/log/apache2/access.log

For Nginx:

tail -f /var/log/nginx/access.log

Filter Logs by HTTP Status Code

grep 404 /var/log/apache2/access.log

This command helps you find all occurrences of a 404 Not Found error in the logs.

Test Website Availability with httping

httping -g https://example.com

This tool continuously pings a website to check for its availability.

Monitor Live Requests with tcpdump

sudo tcpdump -i eth0 port 80 or port 443

This command captures HTTP and HTTPS traffic to analyze status codes in real-time.

Useful resources

Full HTTP status code list: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status
cURL Documentation: https://curl.se/docs/

By mastering HTTP status codes and related troubleshooting commands, IT professionals and cybersecurity experts can diagnose issues faster and ensure a seamless web experience.

References:

Hackers Feeds, Undercode AI

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