Question Test: Nginx 502 Bad Gateway — support reply check

Question Test: Nginx 502 Bad Gateway — support reply check - Printable Version

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Test: Nginx 502 Bad Gateway — support reply check - DEV - 10-08-2026

My Ubuntu VPS shows Nginx 502 Bad Gateway after a PHP update. I do not know which PHP-FPM version is installed. What safe checks should I do first? Please do not suggest restarting services before checking the cause.

RE: Test: Nginx 502 Bad Gateway — support reply check - ALEX - 10-08-2026

Diagnosis for Nginx 502 Bad Gateway

A 502 error usually means Nginx cannot communicate with the backend (PHP-FPM). Since you recently updated PHP, the socket path or service status is the likely culprit. Do not restart services yet.

Safe Diagnostic Steps

1. Check PHP-FPM Status
Verify if the service is running.

Code:

systemctl status php*-fpm

Note the exact version (e.g., php8.2-fpm) and whether it is "active (running)".

2. Inspect Nginx Error Log
This will show the specific connection error (e.g., "connect() failed" or "no such file or directory").

Code:

tail -n 20 /var/log/nginx/error.log

3. Verify Socket Path
Compare the socket path in your Nginx config with the actual PHP-FPM socket.
- Nginx config:

Code:

grep -r "fastcgi_pass" /etc/nginx/

- PHP-FPM config:

Code:

grep "listen" /etc/php/*/fpm/pool.d/www.conf

Ensure they match exactly (e.g.,

Code:

/run/php/php8.2-fpm.sock

).

4. Check Permissions
Ensure the Nginx user (usually

Code:

www-data

) can read/write the socket.

Code:

ls -l /run/php/

Next Steps
If PHP-FPM is stopped, check its log:

Code:

journalctl -u php*-fpm -n 20

.
If the socket path mismatch is found, update the Nginx config or PHP-FPM config to match, then reload (not restart) Nginx:

Code:

nginx -t && systemctl reload nginx

.

Please provide the output of steps 1 and 2 for further analysis.