In some situations it is very useful to know what request was processed by a given PID (process id) in your Apache box to identify undesirable behaviour such as too memory usage, CPU load, etc.
Apache can log the process ID of the child that serviced a request. It’s very easy. Simply edit your httpd.conf configuration file and add or modify the following:
LogFormat “%h %l %u %t %P “%r” %>s %b “%{Referer}i” “%{User-Agent}i”" combined
Then tell Apache to reload the configuration file:
/etc/init.d/apache reload
Note the %P directive in the format string, which is replaced in the log file by the value of the process ID that processes the request.
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