A second NGINX site usually returns 404 for one of two reasons: the request is being handled by a different server block, or the correct block is selected but its root, alias, location, or try_files rules point to a file that does not exist. Prove which server block received the request first, then verify the filesystem mapping.
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Why the second virtual host returns 404
NGINX makes two separate decisions for every request. First, it selects a server block using the local address, listening port, and request host name. Only after that does it choose a location and translate the URI into a file path or upstream request.
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If the intended block did receive the request, a 404 normally means that the URI did not resolve to a readable file or directory. NGINX’s static-content behavior returns 404 when the requested file is missing. A rule such as try_files $uri $uri/ =404; also deliberately ends in a 404 when neither candidate exists.
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How NGINX chooses a server block
Listening address and port are considered first
Server blocks are grouped by their listen address and port. A block listening on port 80 is not used to serve a request that arrived on port 443, even if both blocks contain the same server_name. The same distinction applies when one site listens on a specific address and another listens on a wildcard address.
Within the matching address-and-port group, NGINX compares the request’s host name with the configured server_name values. The apex name and the www name are separate names unless both are listed.
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default_server is a property of a listen directive, not of a domain name. For a given address and port, the default block handles requests that do not match another name. The first server declared for that address and port is otherwise used as the default when no block is explicitly marked.
NGINX documentation summarizes this rule as: “The default server is a property of the listen port and not of the server name.” That is why changing a server_name alone does not change which block receives unmatched traffic.
A reliable 404 troubleshooting sequence
Follow these checks in order. Each step eliminates a different failure class, so avoid jumping straight to changing root or copying the first site’s configuration.
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Validate syntax before inspecting behavior
Run:
sudo nginx -tDo not reload a configuration that fails this test. A successful result confirms syntax and that NGINX can load the referenced files, but it does not prove that the request will select the intended block.
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Print the complete effective configuration
Run:
sudo nginx -TSearch the output for every
listen,server_name,root,alias,index,location,try_files,return, andproxy_pass. This shows included files and duplicate definitions that may not be obvious from the file you edited.To check how the running binary was built and where it expects its main configuration, inspect:
nginx -V 2>&1The output includes the configure arguments, including the compiled configuration path. Use that path when an installation does not follow the distribution’s usual directory layout.
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Confirm that the site file is active
On Debian or Ubuntu, a file in
/etc/nginx/sites-available/is not active merely because it exists. Check that the intended file is linked into/etc/nginx/sites-enabled/and that the link points to the file you edited.Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.On other systems, inspect the
includedirectives shown bynginx -T. If the file is not included, NGINX cannot select its server block. -
Compare the listen contexts
Check whether both sites listen on the address and port you expect. A typical pair of HTTP blocks may both use
listen 80;. If one useslisten 127.0.0.1:80;and the other useslisten 0.0.0.0:80;, they are not equivalent contexts.Look for accidental or conflicting
default_serverdeclarations. Only one default server can apply to a particular address-and-port combination. A second declaration for the same combination normally causes a configuration error rather than silently selecting the block you intended. -
Test the exact Host header over HTTP
Do not test only by IP address. A request made to an IP uses that IP as the host value, which may select a different server block. Send an explicit host header instead:
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Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.curl -i -H 'Host: second.example' http://SERVER_IP/Test the
wwwname separately:curl -i -H 'Host: www.second.example' http://SERVER_IP/If the first command returns the second site’s expected response but a browser does not, the problem is likely DNS, browser caching, a proxy, or the name being entered differently. If both commands return the same 404 from the first site, inspect server selection and the active configuration.
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Test HTTPS with SNI and the intended address
Port 443 has its own server-selection context. Use
--resolveto connect to a known address while sending the desired HTTPS name through DNS resolution and SNI:curl -ik --resolve second.example:443:SERVER_IP https://second.example/The
-koption bypasses certificate verification for diagnosis only. It does not fix a certificate problem. If HTTP works but this command returns the wrong content or a 404, inspect the port-443 block, its certificate configuration,server_name, locations, and root independently of the port-80 block. -
Check DNS independently of NGINX
Verify that the public name resolves to the address where this NGINX instance is running:
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wwwrecords separately because they can point to different destinations. -
Verify the root, file, and directory traversal permissions
Suppose the selected block contains:
root /var/www/second;For a request to
/withindex index.html;, verify that/var/www/second/index.htmlexists. For a request to/assets/app.css, verify that the corresponding file is at/var/www/second/assets/app.css.Rank #2
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The NGINX worker must be able to traverse every parent directory and read the target file. Check ownership and mode bits on the document root and its parents. A permission problem often appears in the error log as an
open()failure; do not “fix” it by making the entire tree world-writable. -
Read access and error logs while reproducing the request
Use the paths configured by
access_loganderror_log, then make one request and inspect the corresponding entries. The access log can confirm the host, URI, status, and selected server fields when those fields are present in the log format. The error log may show the exact filesystem path NGINX attempted, a permission denial, a rewrite loop, or an upstream failure.Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.If the log format does not include the host or server name, temporarily add those fields to a diagnostic format in a controlled environment, reload after validation, and remove the extra logging when finished.
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Inspect location precedence and try_files
A nested prefix location or regular-expression location can override the
rootyou expected from the server block. Review the complete location tree innginx -T, not onlylocation /.For static content, this common pattern is intentional:
try_files $uri $uri/ =404;NGINX checks whether the URI maps to a file, then to a directory, and returns 404 if neither exists. For an application, the final argument normally needs to be the documented front-controller or named-location fallback rather than
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Reload only after validation, then repeat the same tests
Use:
sudo nginx -t && sudo systemctl reload nginxA reload applies the validated configuration without unnecessarily stopping the service. Repeat the explicit HTTP and HTTPS
curlcommands after the reload. Testing with the same host, path, and address makes it clear whether the change altered server selection or only filesystem lookup.
Minimal working configuration for a static second site
This is a complete baseline for a second static site on HTTP:
server {
listen 80;
server_name second.example www.second.example;
root /var/www/second;
index index.html;
location / {
try_files $uri $uri/ =404;
}
}The two names must be the names clients actually send, and /var/www/second must contain the requested files. If the site should answer only one name, remove the other name rather than relying on an accidental redirect.
After creating the file, confirm that it is included, run sudo nginx -t, reload, and test both host names explicitly. A successful configuration test alone does not verify that index.html exists or that DNS points to this server.
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Root versus alias: the path may not be what you expect
How root builds a path
With root /var/www/second;, NGINX appends the request URI to the root directory. A request for /images/logo.svg is therefore looked up beneath /var/www/second/images/logo.svg, subject to the active location.
How alias changes the mapping
alias replaces the portion matched by the location instead of simply appending the entire URI. For example, an alias inside location /downloads/ must be written with care so that trailing slashes and the matched prefix produce the intended path. Mixing a server-level root with an alias in a nested location is a common reason one URL works while another returns 404.
When diagnosing, write down the exact URI, identify the location that wins, and calculate the resulting filesystem path before changing permissions or moving files.
HTTP and HTTPS must be fixed separately
Port 80 and port 443 do not share server-selection state. A working HTTP block does not automatically configure HTTPS. The HTTPS block needs its own listen 443 context, name matching, certificate settings, root or upstream, locations, and fallback behavior.
Common mistakes include adding the domain only to the port-80 server_name, leaving the port-443 block pointed at the first site’s root, or copying a redirect block that sends traffic to a different host. Use the two explicit curl tests to establish which protocol is failing before editing either block.
Use a deliberate catch-all for unmatched hosts
An explicit catch-all makes accidental host mismatches visible:
server {
listen 80 default_server;
server_name _;
return 404;
}The underscore has no special catch-all meaning. The behavior comes from default_server on the listen directive; the underscore is simply a name that is unlikely to match a real host.
This policy prevents an unknown domain or an IP-based request from displaying another customer’s site. It also makes troubleshooting easier: a 404 from the catch-all indicates that the request did not match a named virtual host, while a 404 from the intended block points toward its path, location, or application rules.
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| Symptom | What it usually proves | Next check |
|---|---|---|
| The second domain shows the first domain’s page | A different server block is probably handling the request. | Run an explicit-Host curl test and inspect listen, server_name, and enabled includes. |
| The response is the catch-all 404 | The host did not match a named block on that address and port. | Check spelling, apex versus www, DNS destination, and the relevant HTTP or HTTPS port. |
| Explicit host testing reaches the second block but still returns 404 | Server selection is working; URI-to-file mapping or application fallback is failing. | Check root, alias, location precedence, try_files, and the requested file. |
| The home page works but assets return 404 | The asset URI may be handled by a different location or mapped to the wrong directory. | Calculate the path produced for the asset URI and inspect nested or regex locations. |
| HTTP works but HTTPS returns 404 | The port-443 block is different, missing, or still points to another site’s configuration. | Use curl --resolve and inspect the complete 443 configuration. |
| Changing a file has no effect | The file may not be included, or NGINX may not have been reloaded. | Confirm it appears in nginx -T, validate, reload, and retest. |
Final verification checklist
- The intended configuration appears in
sudo nginx -T. - The site file is enabled through the appropriate
includepath. - The requested name, including apex or
www, appears in the correctserver_name. - The block listens on the address and port used by the request.
- HTTP and HTTPS have been tested independently.
- DNS resolves each name to the intended server address.
- The active location maps the URI to the expected file or application fallback.
- The document root and every parent directory are traversable by the NGINX worker.
- Logs confirm the host, URI, selected path, and status during reproduction.
sudo nginx -tsucceeds before every reload.
The key distinction is simple: server selection happens before filesystem lookup. Prove which block received the request, then prove that block can resolve the URI. That method fixes both classes of second-virtual-host 404 without relying on guesswork.
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