php-fpm doesn't save error logs for a pool

Question

I'm using php-fpm with Caddy and I cannot make php-fpm log errors. Previously I used nginx and nginx captures and displays php errors in its own logs quite nicely, so I never had an issue, but with caddy I decided to enable php-fpm error log, and it just... doesn't work. But let's start from the beginning:

OS: Ubuntu 22.04.1

App: Symfony 7.1 with monolog (mentioning it in case it stops error propagation or whatever)

Caddy v2.8.4 config:

[REDACTED] { tls [REDACTED] root * [REDACTED] file_server php_fastcgi unix//var/run/php/php8.3-fpm.sock log { output file /var/log/caddy/[REDACTED].log level ERROR } 

php-fpm 8.3.12 pool configuration:

 listen = /var/run/php/php8.3-fpm.sock listen.owner = [REDACTED] listen.group = www-data pm = dynamic pm.max_children = 5 pm.start_servers = 2 pm.min_spare_servers = 1 pm.max_spare_servers = 3 user = [REDACTED] group = www-data php_value[memory_limit] = 8G catch_workers_output = yes php_flag[display_errors] = on php_admin_value[error_log] = /var/log/php-fpm/[REDACTED].log php_admin_flag[log_errors] = on 

The main php-fpm log works just fine, but it just contains information about service restarts basically, so it's not very useful. The log belonging to the pool is not saved.

What I did:

• I made sure that permissions and ownership of the log files are correctly set. Log file exists. I touched it, and copy-pasted paths to avoid any typos. The /var/log/php-fpm directory is 777 just as the log file. It's temporary to exclude any permission reasons.
• I can see in phpinfo that values set in the pool configuration take effect.
• I restarted everything.
• When I visit a page returning error 500, no log is saved. The logs file is always empty.

Is there anything else am I missing? Does anyone have any idea where I could look at, to figure this out?

Answer 1

I figured it out. To debug this, I introduced a syntax error in the index.php file. I did this to exclude the possibility of Symfony's meddling, and lo and behold: the error was logged. This indicated that it's Symfony that is using its own error handler.

Basically, in dev environment all errors being logged in the [project's root]/var/logs/dev.log file, as per monolog default configuration:

when@dev: monolog: handlers: main: type: stream path: "%kernel.logs_dir%/%kernel.environment%.log" level: debug channels: ["!event"] # uncomment to get logging in your browser # you may have to allow bigger header sizes in your Web server configuration #firephp: # type: firephp # level: info #chromephp: # type: chromephp # level: info console: type: console process_psr_3_messages: false channels: ["!event", "!doctrine", "!console"] 

On prod environment though, the logs are being sent to stderr:

when@prod: monolog: handlers: main: type: fingers_crossed action_level: error handler: nested excluded_http_codes: [404, 405] buffer_size: 50 # How many messages should be saved? Prevent memory leaks nested: type: stream path: php://stderr level: debug formatter: monolog.formatter.json console: type: console process_psr_3_messages: false channels: ["!event", "!doctrine"] deprecation: type: stream channels: [deprecation] path: php://stderr formatter: monolog.formatter.json 

So yeah, Symfony basically handles errors itself, so php-fpm is not logging them.

Here is a post of the Symfony's author about why logging to stderr is recommended: https://symfony.com/blog/logging-in-symfony-and-the-cloud