If you are upgrading from CentOS5 to CentOS6 and attempt to start httpd, you may come across a message similar to: “Starting httpd: httpd: Syntax error on line 196 of /etc/httpd/conf/httpd.conf: Cannot load /etc/httpd/modules/mod_file_cache.so into server: /etc/httpd/modules/mod_file_cache.so: cannot open shared object file: No such file or directory”. Apparently the removal of some apache mods was an upstream decision which CentOS passed through to us. You can find more information here.

The quick fix is to remove these references from your httpd.conf file, however if you depend on these modules being available, you will have to download and compile manually.