The kernel modules required for booting the system up are part of an initial ramdisk which is automatically loaded into the memory by a boot loader. The ramdisk contains enough modules to mount the root filesystem and to initialize essential devices like keyboard, console or various expansion cards. The boot process then continues with running the init process.
During the next phase, the other modules referenced by the operating system are loaded automatically. The modules are called by their aliases specified and set in the /etc/modprobe.conf configuration file. The typical alias is e.g. eth0 for a network interface card or usb-controller for an USB controller.
If we need to load some specific module during the system boot and there isn't a way to reference it we have a few choices how to do it.
- Place a particular modprobe command to the /etc/rc.d/rc.local script which is called at the end of the whole boot process. But it is likely to be late at this phase.
- Or better, place the command in the /etc/rc.modules file which is read and executed by the /etc/rc.d/rc.sysinit initialization script during the system initialization phase. It may be better to load the modules as soon as possible.
The /etc/rc.modules does not exist by default, so at first create it and make it executable. I think the first method is commonly used by many of us but the second one is in my opinion more systematical.