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If Nginx is installed but your site will not load, work from the network edge inward: prove that the request reaches the correct IP and port, confirm which server block handles the Host header, then fix the static-file or reverse-proxy path. Run sudo nginx -t, inspect the actual listeners and expanded configuration, make one controlled curl request, and read the access and error logs before changing more settings.
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What a running Nginx service does—and does not—prove
An active Nginx process only proves that a worker started successfully. It does not prove that Nginx is listening on the address your browser is using, that DNS points to this machine, that the intended configuration file was loaded, or that the request matches the right server block. A browser can therefore show the default welcome page, return a 404, report a 502, or fail before Nginx sees the request at all.
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- Client and DNS: the hostname must resolve to the expected public address.
- Listener: a firewall and Nginx must accept the destination IP and port.
- Server selection: the address, port, and HTTP Host header must select the intended server block.
- Content handler: a static root or rewrite must map the URI to content.
- Upstream: a reverse proxy must reach the backend protocol, hostname, and port.
- TLS: HTTPS must reach the correct SSL listener with readable certificate and key files.
Fix the earliest failed boundary. Changing application code will not repair a DNS or listener problem, and changing DNS will not repair a 502 caused by a stopped backend.
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Start with evidence, not another reload
Validate the configuration and discover the paths
Before every reload, test the configuration that Nginx will actually parse:
sudo nginx -tA successful test reports that the syntax is okay and the test is successful. If it names an include file, directive, permission problem, or line number, repair that exact file first. Do not keep reloading a configuration that has not passed this test.
Builds installed by packages, source compilation, containers, and control panels can use different files and log locations. Ask the binary where it was built to look:
nginx -V 2>&1Inspect the output for --conf-path, --error-log-path, and, when you need debug logging, --with-debug. A common Linux error log is /var/log/nginx/error.log, but the compiled path and any per-server error_log directive take precedence. Use the same binary and privilege level that your service manager uses; otherwise you may test one installation while the service runs another.
Confirm the service and the real listening sockets
On a system using systemd, check the service state and recent startup messages:
sudo systemctl status nginx --no-pager
sudo journalctl -u nginx --since '-15 minutes' --no-pagerAn active status can coexist with a listener bound only to loopback, only to IPv6, or to an unexpected port. Inspect sockets directly:
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The Nginx web-server documentation describes listen as the directive that selects the IP address and port (or a Unix socket) for requests. Omitted values have context-dependent defaults, so write the intended address and port explicitly when diagnosing ambiguity.
Prove which configuration Nginx loaded
Expand includes with nginx -T
Distribution packages commonly include a main file plus files from an enabled-directory. A file sitting in an available directory is irrelevant until it is included. Print the complete parsed configuration:
sudo nginx -TSearch that output for every server { block, its listen lines, server_name, root, location, proxy_pass, and any default_server. Look for duplicate or conflicting blocks and for an include statement pointing to a different directory than the one you edited.
Understand address, port, and Host matching
Nginx first groups candidates by the local address and port selected by listen. It then compares the HTTP Host header to server_name. When no name matches, the request is handled by the default server for that address and port—explicitly marked with default_server, or otherwise the first matching server block.
A minimal static site block might look like this:
server {
listen 80;
server_name example.com www.example.com;
root /var/www/example;
index index.html;
location / {
try_files $uri $uri/ =404;
}
}The welcome page means the request reached Nginx but selected a different block, or your intended block was never loaded. It is not evidence that the document root is correct.
Test selection locally with an explicit Host header
Bypass public DNS and test the server-selection decision directly:
curl -I -H 'Host: example.com' http://127.0.0.1/Then test the machine’s public address while preserving the same Host header:
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curl -I -H 'Host: example.com' http://PUBLIC_IP/Replace PUBLIC_IP with the address assigned to the server. A different status, response header, or body between these requests identifies a boundary outside the local server block—often a firewall, load balancer, NAT rule, or another endpoint answering the public address. Use curl -v when you need to see connection, redirect, and response details.
Separate static-file problems from reverse-proxy problems
Static sites: verify root, URI mapping, and permissions
For a static site, take the URI from the access log and map it to the configured root. With root /var/www/example, a request for /about.html normally looks for /var/www/example/about.html. Check the file and each parent directory:
sudo ls -l /var/www/example/about.html
namei -l /var/www/example/about.htmlThe Nginx worker must be able to traverse every parent directory and read the file. Correct ownership and mode for your distribution’s Nginx user, rather than a blanket writable mode, is the safer fix. Also inspect try_files, rewrites, trailing-slash redirects, and case-sensitive filenames. A single-page application often needs a deliberate fallback such as try_files $uri $uri/ /index.html;; a plain file server should generally return 404 for a missing path instead of hiding deployment errors with a fallback.
Reverse proxies: prove the upstream from the Nginx host
A proxy configuration adds another network hop:
server {
listen 80;
server_name app.example.com;
location / {
proxy_pass http://127.0.0.1:3000;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}
}Check that proxy_pass is inside the intended location, uses the correct protocol, resolves the hostname, and points to the port where the application is actually listening. Test the backend from the Nginx machine, not from your laptop:
curl -v http://127.0.0.1:3000/
sudo ss -ltnp | grep ':3000'If the backend binds only to a private container or Unix socket, the address in proxy_pass must match that arrangement. A service can be healthy from inside a container while unreachable from the Nginx network namespace.
Use logs while making one controlled request
Logging is the fastest way to distinguish what Nginx received from what it could not complete. F5 NGINX documentation describes logging as essential for troubleshooting and understanding traffic flow.
In one terminal, follow the relevant files:
sudo tail -F /var/log/nginx/access.log /var/log/nginx/error.logIf those files do not exist, use the paths reported by nginx -V and the access_log or error_log directives in nginx -T. In another terminal, make exactly one request:
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curl -v -H 'Host: example.com' http://127.0.0.1/Match the timestamp, request method, Host, URI, status, and upstream message. The access log proves that a request reached a particular Nginx instance. The error log explains failures such as permission denial, missing files, upstream connection refusal, name-resolution errors, or SSL key problems. Repeat with the public hostname only after the local test is understood, so you do not mix several requests together.
Interpret the symptom before choosing a fix
| Symptom | Most likely boundary | Checks and corrective action |
|---|---|---|
| Connection refused | No process is accepting that address and port, or an active reject is in front of Nginx. | Check ss -ltnp, the listen address, host firewall, cloud security group, load balancer, and NAT. If proxying, test the upstream separately. |
| Connection timeout | Packets are being dropped or routed to the wrong endpoint. | Verify DNS, public IP, firewall rules, security groups, and any reverse proxy or load balancer. A timeout usually occurs before Nginx can write an access-log entry. |
| Default Nginx welcome page or another site | The request reached Nginx but selected the default or another server block. | Compare listen, server_name, default_server, enabled includes, and the Host header in nginx -T. |
| 404 Not Found | The selected block cannot map the URI to content. | Verify root, the exact case-sensitive filename, permissions, try_files, rewrites, and the URI recorded in the access log. |
| 502 Bad Gateway | Nginx reached the proxy stage but could not obtain a valid upstream response. | Check the proxy_pass protocol, hostname, port, DNS resolution, backend process, bind address, and error-log message. |
| 504 Gateway Timeout | The upstream did not respond within the configured time. | Test the backend directly, inspect application logs and network policy, and change timeout values only after proving the backend is reachable but slow. |
| HTTPS certificate or handshake failure | The request reached the wrong TLS block, or certificate, key, protocol, or DNS does not match. | Confirm listen 443 ssl, certificate and key paths and permissions, the requested hostname, and the endpoint returned by DNS. Use the exact browser or Nginx error rather than guessing. |
Fix the common configuration failures
The intended server block is not enabled
Many Linux layouts separate available files from enabled files. Confirm that the main configuration includes the directory containing your site and that the site file is actually linked or included. After enabling it, run sudo nginx -t and reload. Do not delete the default block until your replacement answers correctly; keeping it as a known fallback makes selection mistakes visible.
The server_name does not match the real request
Include every hostname clients use, such as the apex name and its www form, or deliberately redirect one to the other. A typo, an unlisted alias, or a request made by IP address can send traffic to the default server. Test each name with an explicit Host header before relying on browser redirects.
The root is correct but access is denied
A 403 or an error-log permission message means the worker cannot traverse a directory or read the target. Check parent-directory execute permission, file read permission, ownership, and any mandatory access-control policy used by the operating system. Fix the narrowest permission that permits reads; do not make the whole web tree world-writable.
The proxy target is wrong or stopped
Read the exact upstream error. “Connection refused” usually means no process is listening at that address and port. “No such host” points to DNS or a misspelled upstream name. A response with an invalid header can indicate that the target is speaking a different protocol than the one in proxy_pass. Correct the backend or the proxy target, then test it locally before reloading.
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HTTPS-specific checks
HTTP and HTTPS can select different server blocks. Verify that DNS for the hostname reaches the expected endpoint and that the TLS request selects the block containing listen 443 ssl. Check that the certificate and private-key paths in the loaded configuration exist and are readable by the Nginx master process. A certificate for one hostname will not satisfy another hostname merely because both point to the same IP. If HTTP works but HTTPS fails, capture the exact browser message and correlate it with the Nginx error log; certificate mismatch, unreadable key, expired certificate, and handshake protocol errors require different fixes.
Escalate to debug logging only when normal logs are insufficient
Debug logging is noisy and should be temporary. First check whether the binary includes it:
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nginx -V 2>&1 | tr ' ' 'n' | grep -- '--with-debug'If --with-debug is present, set an error_log directive to the debug level in the narrowest useful context, preferably the affected server block or location. For example:
server {
listen 80;
server_name example.com;
error_log /var/log/nginx/example-debug.log debug;
...
}Run sudo nginx -t, reload, make one request, and remove or lower the debug directive afterward. Nginx’s debugging guidance warns that a more specific error_log without the debug level overrides a broader debug setting in that context, effectively disabling debugging there. Debugging helps expose request parsing, server selection, rewrite processing, and upstream connection details that normal error levels omit.
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Reload safely and compare the result
A configuration change normally needs a reload, not a full restart:
sudo nginx -t && sudo systemctl reload nginxThe test prevents a bad file from being applied. A restart is reserved for cases where the service manager or a changed runtime dependency specifically requires it; restarting can create avoidable downtime and does not fix an incorrect server block.
Evaluate two possible fixes using four questions:
- Where does the failure occur? Client/DNS, listener, server selection, static mapping, or upstream.
- Is the change limited and reversible? Prefer a single server block or directive over a global change.
- What operation is required? A validated reload is safer than a restart when the worker binary and service are healthy.
- What evidence changed? Confirm the expected access-log status and the disappearance of the relevant error-log entry.
A compact end-to-end checklist
- Run
sudo nginx -tand fix the exact reported file or line. - Run
nginx -Vto identify the loaded configuration, error-log path, and debug support. - Check service state and startup messages with
systemctlor the equivalent service manager. - Inspect
ss -ltnpand compare listeners with everylistendirective. - Print
sudo nginx -T; verify includes,server_name,default_server, root, locations, and proxy targets. - Use
curl -I -H 'Host: your-hostname' http://127.0.0.1/to prove local server selection. - For static content, verify root-to-file mapping and permissions.
- For a proxy, connect to the upstream directly from the Nginx host.
- Tail access and error logs while making one controlled request.
- Only after local behavior is correct, test DNS, firewalls, public routing, and HTTPS.
- Use temporary debug logging only if normal logs cannot explain the failure.
If the local Host-header test returns the intended site but the public hostname does not, stop editing Nginx and investigate DNS, firewall rules, security groups, NAT, a load balancer, or the managed hosting endpoint in front of it. If the local test returns the welcome page, 404, or 502, the evidence is already on the server: correct selection, content mapping, or upstream reachability before changing anything outside Nginx.
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