How To Troubleshoot Common Nginx Errors
Common commands to troubleshoot nginx:
-
sudo cat /var/log/nginx/error.log: This is used to print a log with a list of errors and details about them. -
sudo nginx -t: This is used to check for syntax error in configuration. -
systemctl status nginx: This is used to check if the Nginx service is active or inactive.
Troubleshooting with the Error Log
To get a full overview of the nginx errors happening, run:
sudo cat /var/log/nginx/error.log
Above command results in error log. Example:
2022/11/28 23:58:22 [emerg] 168641#168641: invalid host in "[::]443" of the "listen" directive in /etc/nginx/sites-enabled/test.do-community.com:12
2022/11/28 23:59:44 [emerg] 168664#168664: invalid number of arguments in "root" directive in /etc/nginx/sites-enabled/test.do-community.com:4
2022/11/29 00:00:19 [emerg] 168701#168701: "server" directive is not allowed here in /etc/nginx/sites-enabled/test.do-community.com:6
2024/08/03 10:41:37 [notice] 28504#28504: using inherited sockets from "6;7;"
2024/08/03 10:52:29 [notice] 31898#31898: signal process started
2024/08/03 11:02:04 [error] 31899#31899: *5 open() "/var/www/tech.local/foss" failed (2: No such file or directory), client: 127.0.0.1, server: tech.local, request: "GET /foss HTTP/1.1", host: "localhost", referrer: "http://localhost/"
2024/08/03 11:02:45 [error] 31899#31899: *5 open() "/var/www/tech.local/foss" failed (2: No such file or directory), client: 127.0.0.1, server: tech.local, request: "GET /foss HTTP/1.1", host: "localhost", referrer: "http://localhost/"
2024/08/03 11:05:54 [error] 31899#31899: *7 open() "/var/www/tech.local/foss" failed (2: No such file or directory), client: 127.0.0.1, server: tech.local, request: "GET /foss HTTP/1.1", host: "localhost", referrer: "http://localhost/"
2024/08/03 11:28:19 [notice] 43309#43309: signal process started
2024/08/03 11:28:30 [crit] 43310#43310: *31 connect() to unix:/this/is/error failed (2: No such file or directory) while connecting to upstream, client: 127.0.0.1, server: tech.local, request: "GET /500error HTTP/1.1", upstream: "fastcgi://unix:/this/is/error:", host: "localhost"
2024/08/03 11:37:53 [crit] 43310#43310: *37 connect() to unix:/this/is/error failed (2: No such file or directory) while connecting to upstream, client: 127.0.0.1, server: tech.local, request: "GET /500error HTTP/1.1", upstream: "fastcgi://unix:/this/is/error:", host: "localhost"
The log provides key information about the specific error.
The error message is divided into:
- first part: date and time
- second part [...]: provides types of error message, e.g: notice, crit, error, emerg(emergency) etc.
- last part: error message itself (with what file and specific line can be found)
Checking for Syntax Errors
Most common errors nginx has to do with syntax in configuration error. To check syntax error, run:
sudo nginx -t
The output if everything is ok:
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
If there is syntax errors, example of log:
[emerg] invalid host in "[::]443" of the "listen" directive in /etc/nginx/sites-enabled/test.do-community.com:12
nginx: configuration file /etc/nginx/nginx.conf test failed
After verifying syntax is correct always reload nginx. Command:
sudo systemctl reload nginx
# OR
sudo nginx -s reload
Troubleshooting with systemctl status nginx
Always verify if nginx service is active and working on your system. Use systemd init system:
systemctl status nginx
If your service is running, it will read as active (running) in output.
If your service is not running, it will read as inactive (dead) in the output. If that happens restart Nginx service:
sudo systemctl restart nginx
Verify if it has restarted with:
systemctl status nginx
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