Kernel modules are usually loaded directly by the facility that requires them, which is given correct settings in the /etc/modprobe.conf file. However, it is sometimes necessary to explicitly force the loading of a module at boot time.
Red Hat Enterprise Linux checks for the existence of the /etc/rc.modules file at boot time, which contains various commands to load modules. The rc.modules should be used, and not rc.local because rc.modules is executed earlier in the boot process.
For example, the following commands configure loading of the foo module at boot time (as root):
# echo modprobe foo >> /etc/rc.modules # chmod +x /etc/rc.modules
This approach is not necessary for network and SCSI interfaces because they have their own specific mechanisms.