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If Nginx is installed but your domain does not show the site you expect, work from the network boundary inward: confirm that the request reaches the machine, verify the address and port Nginx is listening on, prove which server block matches the Host header, then test either the static files or the proxied application. A running Nginx process alone proves none of those things. The fastest evidence is usually in the loaded configuration and the access and error logs.
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What a running Nginx process does—and does not—prove
Nginx can be active while your public site still fails for several independent reasons. The service may be listening only on loopback, the firewall may block the public port, DNS may point somewhere else, or the request may reach Nginx but select a different virtual server. A selected server block can then return a 404, serve the default welcome page, or send the request to an unavailable application.
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Think of the request as passing through five boundaries:
- Client and DNS: the browser resolves the hostname and connects to the intended IP address.
- Listener: the machine accepts traffic on the expected address and port.
- Server selection: Nginx matches the address, port, and Host header to a
serverblock. - Content handling: that block maps the URI to a file, rewrite, or location rule.
- Upstream handling: a reverse proxy connects to the application named by
proxy_pass.
Test these boundaries in that order. Changing application code before proving that the correct server block receives the request often hides the real fault.
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Start with a symptom-to-layer map
Use the symptom to choose the first check, but confirm the result in the logs rather than guessing.
| What you see | Most likely boundary | First evidence to collect |
|---|---|---|
| Connection refused | No process is accepting the destination address and port, or a local policy is rejecting it | Listening sockets, service status, firewall and security-group rules |
| Timeout | Traffic is being dropped or routed to the wrong endpoint | DNS result, public IP, firewall/load-balancer path, then listening sockets |
| Nginx welcome page or another site | The request reached Nginx but selected the default or wrong server block | Loaded server_name, listen, default_server, and Host-header tests |
| 404 from Nginx | Wrong root, URI mapping, try_files, rewrite, or location rule |
Selected configuration, exact URI in the access log, filesystem path |
| 502 or 504 | The reverse-proxy path cannot reach or complete with the upstream | Error log, proxy_pass target, DNS, port, and backend process |
| HTTPS warning or handshake failure | Wrong TLS server block, unreadable certificate/key, DNS mismatch, or certificate problem | Port 443 listener, certificate paths, DNS, browser and Nginx error details |
1. Validate the configuration before every reload
Run the syntax test
Use the same privilege and installation that manages the service:
sudo nginx -tA successful test means Nginx can parse the configuration it was asked to load. It does not prove that the intended file is included, that a directory is readable at request time, or that an upstream is reachable. If the command names an include file, directive, permission problem, or syntax error, fix that exact file first. Do not keep reloading a configuration that has not passed the test.
Discover the active paths and build options
Different packages and source builds use different configuration and log locations. Ask the binary which paths it was compiled with:
nginx -V 2>&1Inspect the output for --conf-path, --error-log-path, and, when you need diagnostic logging, --with-debug. A common Linux error log is /var/log/nginx/error.log, but the compiled path and service unit take precedence. If nginx -V appears to describe a different binary than the service uses, check the service unit’s ExecStart path and run the matching binary explicitly.
Print the fully expanded configuration
Includes and distribution-specific snippets can make the file you edited different from the configuration Nginx actually loads:
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2. Confirm the service and the real listening sockets
Check the service manager
On a system using systemd, inspect status and recent messages:
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sudo systemctl status nginx --no-pager
sudo journalctl -u nginx -n 100 --no-pagerOther service managers use different commands, so identify the manager rather than assuming that a process named Nginx is the one serving requests. A failed reload can leave the previous, valid configuration running; the status output and journal show whether the new configuration was accepted.
Inspect sockets, not just processes
List TCP listeners and the owning process:
sudo ss -ltnpCompare the observed address and port with the listen directives in nginx -T. A listener on 127.0.0.1:80 is not equivalent to one on the public interface. An IPv6-only listener is not equivalent to an IPv4 listener, and a service listening on port 8080 will not answer a request sent to port 80 unless another component forwards it.
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Check the path outside Nginx
Resolve the hostname from a client and compare the result with the machine you are inspecting. If DNS points to a load balancer, reverse proxy, CDN, or old server, a perfect local Nginx configuration will not change the public response. Check firewall rules, cloud security groups, and any front-end proxy for the same address and port. A refusal normally indicates that nothing is accepting the connection at that endpoint; a timeout more often indicates filtering or routing.
3. Prove which server block answers
Understand address, port, and Host matching
The listen directive chooses the address and port first. Nginx then uses the request’s Host header to select among server blocks that share that address and port. If no server_name matches, the request is handled by the default server for that listener. This is why an Nginx welcome page is useful evidence: it usually means the connection reached Nginx, but the intended server block was not selected or was not loaded.
Test locally with an explicit Host header
From the Nginx machine, send a request to loopback while naming the site you expect:
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curl -I -H 'Host: example.com' http://PUBLIC_IP/Replace the hostname and address with your values. A correct local response but a wrong public response points to DNS, a front-end proxy, firewalling, or a different destination. A wrong local response indicates Nginx configuration or server selection. Use curl -v when you need to see the connection address, request headers, redirects, and response headers.
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Look for duplicate and default listeners
In the expanded configuration, check for multiple blocks with the same address and port, an unintended default_server, a typo in the hostname, or a broad wildcard that captures the request first. Confirm that the requested spelling, including a www prefix if used, appears in the intended server_name. If both HTTP and HTTPS are configured, test each port separately; a correct HTTP block does not prove that the TLS block is correct.
4. Fix a static-file site
Verify the selected root and URI mapping
For a static site, start with the root in the server block that actually answers. A request for /assets/app.css normally maps beneath that root to a corresponding filesystem path, subject to the active location and rewrite rules. Check the exact path and case:
sudo ls -la /path/to/site
sudo find /path/to/site -maxdepth 2 -type f | headLinux filesystems are case-sensitive. A file named Index.html is not the same as index.html. Verify that the configured index file exists and that a location rule is not replacing the expected path.
Check permissions along the whole path
The Nginx worker must be able to traverse every parent directory and read the requested file. Inspect ownership and mode bits:
namei -l /path/to/site/index.html
sudo -u nginx test -r /path/to/site/index.html && echo readableThe worker account may be named www-data, nginx, or another distribution-specific user. Use the account shown in the loaded user directive or service configuration. Mandatory access-control systems can also deny reads even when Unix permissions look correct; the error log will usually identify such a denial.
Review try_files and rewrites
A single-page application often needs a fallback such as try_files, while a conventional site may need a real file for every URI. A malformed fallback can turn valid routes into 404s or internal redirect loops. Inspect the active order of location blocks and rewrite directives, then request the failing URI directly and match it to the access-log entry. Make the smallest change in the intended server block, run nginx -t, and reload.
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Read the upstream error literally
When Nginx returns 502 or 504, treat the upstream path as the primary suspect until the error log shows otherwise. The proxy_pass directive forwards the request to a configured protocol, hostname, and port. The target must be reachable from the Nginx host, not merely from your laptop.
sudo ss -ltnp
getent hosts backend.example.internal
curl -v http://127.0.0.1:3000/healthUse the actual upstream hostname and port in the last command. If the backend listens only on a Unix socket, the proxy configuration must use the socket form supported by your setup rather than a TCP address.
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Check protocol, port, and name resolution
An HTTP upstream and an HTTPS upstream are not interchangeable. Confirm that the scheme in proxy_pass matches what the backend speaks, that the port is open, and that DNS resolves from the Nginx machine. A name that resolves in an interactive shell can still fail under a restricted resolver configuration or container network. Test the exact name and address used by Nginx.
Confirm the location scope
Make sure proxy_pass is inside the intended location and that another more-specific location is not serving the request as a file. Trailing slashes can change how Nginx combines the location prefix and upstream URI, so compare the requested path with the backend’s access log. If the backend process is stopped, start or repair it first; if it is healthy locally but unreachable from Nginx, investigate bind addresses, network namespaces, firewall rules, and container bridges.
6. Watch access and error logs during one controlled request
Find the files actually in use
Nginx documentation describes logging as essential for troubleshooting traffic flow. The default Linux error-log path is often /var/log/nginx/error.log, but the exact location depends on the build and installation method. The access log can be set globally or inside a server or location block, so inspect the loaded access_log and error_log directives rather than assuming a filename.
Tail logs and make one request
In one terminal, follow the relevant files:
sudo tail -F /var/log/nginx/access.log /var/log/nginx/error.logIn a second terminal, issue one request with verbose output:
curl -v -H 'Host: example.com' http://127.0.0.1/Match the timestamp, Host, URI, status, request length, and upstream message. The access log proves what Nginx returned; the error log explains why it could not complete the request. If no access entry appears, the request did not reach that Nginx instance or the request is being stopped before the configured log point.
Use status codes as evidence, not diagnoses
A 404 can be generated by Nginx or by an upstream application. A 500 can come from the backend even when Nginx is functioning. Inspect response headers and both logs to identify the component that produced the status. Record one failing request before changing configuration so you can verify whether the change altered the actual path.
7. Interpret common failure branches
Connection refused
- Confirm the destination IP and port with a verbose client request.
- Check
ss -ltnpfor a listener on that exact address and port. - Check service status and the journal for a failed start or reload.
- Check host firewall, cloud security-group, load-balancer, and reverse-proxy rules.
- If Nginx is proxying, separately test the upstream from the Nginx host.
A refusal means the TCP connection reached an endpoint that rejected it; it does not identify whether the endpoint was the intended server.
Timeout
Compare DNS answers from the client and the server’s public addresses. Confirm routing and firewall policy before editing Nginx. If a load balancer or CDN fronts the host, test the origin directly from an allowed network and inspect the front-end health check. Only after traffic reaches the machine should you debug listeners and server blocks.
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Default Nginx page or another site
Inspect nginx -T for the intended include, duplicate listeners, a typo in server_name, and an unintended default_server. Repeat the explicit Host-header test. If the local request selects the right site but the public request does not, DNS or the front-end endpoint is selecting a different machine.
404
Verify the selected root, exact URI-to-file mapping, index file, try_files, and rewrites. Use the access log to capture the exact URI, including URL encoding and trailing slashes. Check whether the 404 response contains headers or a body identifying an upstream application rather than Nginx.
502 or 504
Read the error-log line for connection refusal, timeout, name-resolution failure, or protocol error. Verify the proxy_pass scheme, hostname, port, backend bind address, and process health from the Nginx host. A 504 generally means the connection or response did not complete within the relevant timeout; increasing timeouts before proving reachability can conceal a stopped or misaddressed backend.
8. Repair HTTPS separately from HTTP
HTTPS uses a different listener and commonly a different server block. Confirm that Nginx listens on the expected TLS address with a listen 443 ssl directive and that the request reaches the intended block. Check that the certificate and key paths in the loaded configuration exist and are readable by the Nginx master process. A certificate can be present while still being expired, issued for another hostname, or missing an intermediate certificate; use the browser’s exact certificate error and the Nginx error log to distinguish those cases.
Verify DNS before changing certificates. If the hostname resolves to another endpoint, you may be inspecting a valid certificate on the wrong machine. Test the origin locally only after selecting the correct TLS server block, and avoid disabling certificate verification as a permanent fix.
9. Escalate to debug logging only when normal logs are insufficient
Normal error and access logs should be your first evidence. Debug logging is more verbose and can expose request details, so enable it temporarily and restrict access to the resulting files.
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Check whether the binary supports debug mode
nginx -V 2>&1 | grep -- --with-debugIf --with-debug is present, set an error_log directive to the debug level in the narrowest useful context, such as the affected server block, then validate and reload:
sudo nginx -t
sudo systemctl reload nginxDebug logging can be enabled globally or for a particular server block. A more-specific error_log without the debug level overrides the parent setting and disables debugging in that context, so inspect nested blocks when no debug entries appear. Reproduce one request, collect the relevant lines, restore the normal level, validate again, and reload.
10. Choose the smallest safe fix
When two fixes seem possible, compare them on four questions:
- Failure location: Is the problem at DNS/client reachability, the listener, server selection, static content, or the upstream?
- Scope and reversibility: Can you change only the affected server block instead of a global include?
- Reload versus restart: Can a configuration-only change be applied with a validated reload, or does the service need a restart because the process or package is unhealthy?
- Observable evidence: Will the access and error logs show the intended request before and after the change?
Configuration edits normally require nginx -t followed by a reload. A restart interrupts workers and should be reserved for cases that require it, such as a failed service process or a package-level change. Keep a copy of the last known-good configuration and change one variable at a time.
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- Resolve the domain and confirm it points to the endpoint you are testing.
- Run
sudo nginx -tand fix the exact reported file or directive. - Run
nginx -Vto identify the binary, configuration path, log path, and debug support. - Run
sudo nginx -Tand verify that the intended site file is loaded. - Check service status and the journal for failed starts or reloads.
- Run
sudo ss -ltnpand compare listeners with every relevantlistendirective. - Test loopback with an explicit Host header, then test the public IP with the same header.
- For static content, verify root, URI mapping, index files, ownership, permissions, and rewrite rules.
- For a proxy, test the exact upstream protocol, hostname, port, and health endpoint from the Nginx host.
- Tail the active access and error logs while making one controlled
curl -vrequest. - Handle HTTPS as its own listener and server-selection problem, including certificate readability and DNS.
- Enable debug logging only if the normal logs cannot identify the failing boundary, then turn it off after reproduction.
This sequence turns “Nginx is installed but my site will not load” into a bounded question: did the request arrive, which listener accepted it, which server block matched, and did that block successfully serve a file or reach its upstream?
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