Kernel, Cron, and User Administration, Part 1 - Kernel Concepts
(Page 8 of 11 )
You will need to understand some basic kernel concepts before you can compile your own kernel. Kernels can be organized as one big unit, or as a lot of interconnected pieces. Kernels are called up by boot loaders when you boot your computer.
Monolithic versus Modular A
monolithic kernel is a kernel where all the device modules are built directly into the kernel.
Modular kernels have many of their devices built as separate loadable modules. Monolithic kernels can communicate with devices faster, since modular kernels can talk to the hardware only indirectly through a module table. Unfortunately, monolithic Linux kernels are huge. Bigger kernels reduce available RAM. In addition, some systems just can’t boot a kernel that’s too large.
There used to be advantages to a monolithic kernel. Linux once had problems loading modular kernels for some hardware. With a monolithic kernel, the drivers would already be there. But now modular kernels load new drivers a lot more reliably.
A modular kernel has greater flexibility. You can compile almost all your drivers as modules, and then each module can be inserted into the kernel whenever you need it. Modules keep the initial kernel size low, which decreases the boot time and improves overall performance. If Linux has trouble loading a kernel module, you can use the modprobe or insmod commands to load modules as needed.
Updating the Kernel Updating the kernel is not as difficult as it looks. You should always keep a copy of your old kernel around in case you make a mistake. New kernels are handled by installing the newly built kernel in
/boot and then adding another boot option to your boot loader configuration file
(/etc/grub.conf or
/etc/lilo.conf) for the new kernel. GRUB or LILO treats the new kernel as if it were an entirely new operating system.
If you install the new kernel directly from a Red Hat configured RPM, it updates your boot loader automatically.
If you do make a drastic mistake and the kernel doesn’t boot, then you can simply reboot the server and select your old kernel at the GRUB or LILO prompt. You should also save your kernel configuration files so that you can easily copy to the newer kernels and use them as a guideline. This will be discussed in more detail later in this chapter.
 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.
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