s %b \"%{Referer}i\" \"%{User-Agent}i\" PID:%P TID:%{tid}P" combined LogFormat "%v %h %l %u..." />

Как научить Apache писать PID-процесса в access-log

/etc/httpd/conf/httpd.conf:
<IfModule log_config_module>
LogFormat "%v %h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" PID:%P TID:%{tid}P" combined
LogFormat "%v %h %l %u %t \"%r\" %>s %b" common
<IfModule logio_module>