On linux, the apache error log is found in dir /var/log/httpd/.

I'm using Linux (Slackware) and the (main) error log is in /var/log/apache2/error_log.

The sysadmin can put that directory where ever he/she wants.

On the other hand, foreach site I always create a dedicated /logs dir under the site directory (not a public directory). This way I don't fill up the main error_log and makes it easier to follow errors on the web site I'm currently working.

I do this when I configure a new site on Apache:

<VirtualHost ....>
  ......
  ErrorLog /path/to/website/error_log
  ....
</VirtualHost>
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