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Today I found myself on someone else’s Apache HTTPD server needing to locate the parent error_log (the one where apache records its startup). The server has a dizzying array of virtual hosts configured using a web of configuration files pulled in with Include directives. Using the configuration files to untangle which is the default virtual host and what it is using for ErrorLog was unfruitful.

My understanding is that the error_log I’m looking is the stderr for the parent apache process. So, punting, I used lsof to see where the parent process was writing stderr, a.k.a. file descriptor 2, which will be reported as ‘2w’ by lsof.

First lookup the parent httpd process. The server runs CentOS using the init system:

[root@xenu ~]# ps -u root | grep httpd
10226 ? 00:07:04 httpd

Using lsof, see what pid 10226 is using for stderr:

[root@xenu ~]# lsof -p 10226 |grep ' 2w'
httpd   10226 root    2w   REG  8,64     9411     49196 /files/www/virtualhost/RedProject/release1.0/logs/error_log

Another approach is to check the /proc filesystem:

[root@xenu ~]# ls -l /proc/10226/fd/2
l-wx------ 1 root root 64 Apr  1 16:47 /proc/10226/fd/2 -> /files/www/virtualhost/RedProject/release1.0/logs/error_log

Yep, that’s the one.

[root@xenu ~]# grep resuming /files/www/virtualhost/RedProject/release1.0/logs/error_log
[Tue Feb 21 12:52:55 2012] [notice] Apache/2.2.3 (CentOS) configured -- resuming normal operations
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