Cannot get WordPress debug.log working.

[ChrisTaylorDeveloper]

I cannot get WordPress in this Docker image to create a debug.log file. I am using the Docker Compose example from here https://hub.docker.com/_/wordpress

I set the WORDPRESS_DEBUG environment variable, in the wordpress service definition and then call the error_log('...') function from a plugin. No debug.log file appears in the wp-content folder or anywhere else that I can find.

Any advice please?

[tianon]

I think if you want debug.log, you might also need to add define( 'WP_DEBUG_LOG', true ); to wp-config as noted in https://developer.wordpress.org/advanced-administration/debug/debug-wordpress/ (most easily via WORDPRESS_CONFIG_EXTRA 👀)

[yosifkit]

Unless you are overriding debug_log in the php configuration, then it will not be in a file and just show up in docker logs:

wordpress/Dockerfile.template

Line 168 in 654752d

echo 'error_log = /dev/stderr'; \

[ChrisTaylorDeveloper]

Let me check if I can see my log messages in docker logs. Thank you.

[ChrisTaylorDeveloper]

My log messages do appear in the docker logs. And they appear even when I do not set WORDPRESS_DEBUG.
So, that begs the question, what is the function of WORDPRESS_DEBUG? Is there some functionality missing in the Image? Happy to open an Issue if required.

[tianon]

To be clear, you see your error_log invocations with or without it, right? I think that's because error_log is a PHP construct, not a WordPress specific one: https://www.php.net/manual/en/function.error-log.php

(and WORDPRESS_DEBUG controls WordPress behavior itself, as described in https://developer.wordpress.org/advanced-administration/debug/debug-wordpress/#wp_debug)

[ChrisTaylorDeveloper]

Yes, I see the result of error_log() whether or not I start the container with WORDPRESS_DEBUG.

To get /wp-content/debug.log working, I think it would be reasonable to start the container with both WORDPRESS_DEBUG and (a new long-form) WORDPRESS_DEBUG_LOG. Or, pass WP_DEBUG_LOG via WORDPRESS_CONFIG_EXTRA. Either way, the Image would need to be adjusted to stop using stderr I guess?

[tianon]

WordPress itself adjusts the PHP configuration automatically based on WP_DEBUG_LOG: https://github.com/WordPress/WordPress/blob/1dc3f878703ff788a5dc1b06efda6c665554dcb3/wp-includes/load.php#L593-L596

We do not plan to add more environment variables, so WORDPRESS_CONFIG_EXTRA is going to remain our official answer for how to use this upstream WordPress functionality.

[ChrisTaylorDeveloper]

I have this working now. Thank you.