Format of messages posted to error_log?

Scott Snow scott.snow at
Tue Apr 12 15:29:57 UTC 2022

Is there documentation for the format of error messages nginx posted to error_log?
Specifically, following the level in square brackets are two numbers separated by '#'; what do these represent?
For instance, the message on the page Advanced Configuration with Snippets | NGINX Ingress Controller<> begins with "[emerg] 31:31:"
Why I'm asking is for purposes of documentation; a system using nginx routes these messages to syslog; the design document for the module responsible for publishing the messages gives the format and examples. The example for nginx errors begins:
<131>Oct 24 18:17:47 imx7d-zoll-resus nginx: 2018/10/24 18:17:47 [error] 3105#0: *11 connect() failed (111: Connection refused) while connecting ...

We have a format and examples for each of syslog-ng, gunicorn access, gunicorn error, and nginx access.
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