After I upgraded package www-servers/apache today, it gave me a message as follow:

 *  Selected default MPM: prefork
 *
 * Please note that you need SysV IPC support in your kernel.
 * Make sure CONFIG_SYSVIPC=y is set.

To check, cd to /usr/src/linix, and check the file .config for CONFIG_SYSVIPC value setting.