The kernel is the heart of the whole operating system. It manages communication with hardware, decides which processes to run, and provides each process with an isolated, virtual address space in which to run. The kernel is what your boot loader, GRUB or LILO, loads into memory. The kernel loads device driver modules. It also allocates hardware resources such as IRQ ports, I/O addresses, and DMA channels. When you recompile your kernel, you can

• Greatly improve the speed at which kernel services operate.
• Build in direct support for commonly used drivers.
• Configure the dynamic loading of appropriate drivers as modules.
• Lower the memory consumption of your kernel by removing unneeded components.
• Configure support for high-end hardware, such as memory above 4GB, hardware array controllers, symmetric multiprocessing (multiple CPU) support, and more.

In essence, you can customize the Linux kernel any way you want. The best way to do it is to make it fit every detail of your hardware. However, you may not need to be so picky. In many cases, where there’s a small update to the kernel, all you need to do is install the updated kernel RPM.

You should compile your kernel with only the elements you need. The more you can leave out, the faster your whole system will run. For example, if you don’t have a sound card, you can remove sound card support from your kernel. By removing unneeded devices, you will

• Decrease the size of the kernel.
• Provide a modest increase in speed for the devices that are present.
• Make more hardware resources (I/O addresses, IRQ ports, and so on) available for other hardware such as network cards, disk controllers, and more.
• Reduce the chance of hardware limits, such as those that may be based on the size of the compressed kernel.

Generally, it is a good idea to have device drivers compiled as modules for any equipment that you may add in the near future. For example, if you may use your Linux computer as a router, you’ll need a second network card, and you can add support for that card to your kernel. For example, if you have a 3Com 3c595 network card installed but you also have some 3Com 3c905 cards in storage, then it may be a good idea to include the 3c905 module. That way, you will just have to swap in the new card and let the module load, causing minimum downtime.

Modules are kernel extensions. They are not compiled directly into the kernel but can be plugged in and removed as needed. When configured as a module, a hardware failure such as that of a network card will not cause the whole system to fail.

This is part one from the fifth chapter of Red Hat Certified Engineer Linux Study Guide (Exam RH302), fourth edition, by Michael Jang. (McGraw-Hill/Osborne, 2004, ISBN: 0-07-225365-7). Check it out at your favorite bookstore today. Buy this book now.