Two-Minute Drill

Here are some of the key points from the certification objectives in Chapter 8.

The Basics of the Kernel

❑	The kernel lies at the heart of the operating system.
❑	Modular kernels, with separate device modules, are more efficient than monolithic kernels, where device drivers are integrated into the kernel.
❑	If you're going to update your kernel, you should keep a copy of your current working kernel.
❑	Linux kernels and related files are stored in the /boot directory.
❑	The /proc directory provides a window to what Linux sees in your computer.
❑	The lsmod command lists currently loaded modules; important related commands are insmod, rmmod, and modprobe.
❑	Basic RHEL modules can be loaded from the kernel-devel RPM.

New Kernels, the Easy Way

❑	Kernel version numbers are organized in major.minor.patch format. Red Hat adds a build number to the Linux kernels that it builds from source code.
❑	It's fairly easy to install a Red Hat kernel from RPM, as long as you remember to install and not upgrade. This allows you to return to the current working kernel if you have a problem.
❑	Sometimes all you need is a kernel patch, which supports upgrades of one patch version number. Unfortunately, patches are not always the best option for Red Hat built kernels.
❑	When you install a Red Hat kernel from RPM, the process should automatically update your GRUB boot loader.

Kernel Sources

❑	Kernel sources can be loaded from the kernel source RPM or from a Linux kernel tarball downloaded from a site such as ftp.kernel.org.
❑	Installing the Red Hat kernel source RPM requires the rpmbuild command.
❑	Once installed, the kernel source tree is available through /usr/src/redhat/BUILD directory.

Recompiling a Kernel

❑	To optimize the Linux kernel, it is a best practice to compile kernels with only needed elements and configure modules for most hardware.
❑	Your current kernel configuration is stored in the config-`uname -r` file in the /boot directory.
❑	You can modify kernel settings from the kernel source code directory with tools that you can open with one of the following commands: make config, make menuconfig, make xconfig, or make gconfig.
❑	Once you've made the proper backups and boot disks and set the EXTRAVERSION variable in your Makefile, you're ready to customize your kernel.
❑	Once you've settled on and saved your changes, run the make rpm command. It should compile your new kernel and create an RPM in the /usr/src/redhat/RPMS directory, which you can use to install your custom kernel.

Advanced Partitioning: Software RAID

❑	Red Hat supports several levels of software RAID, including RAID 0, RAID 1, RAID 5, and RAID 6.
❑	To make software RAID work, you need to designate the partition specifically as such in fdisk or parted.
❑	RAID arrays as configured are shown in /proc/mdstat.
❑	RAID arrays can be created and modified with the mdadm command.

Advanced Partitioning: Logical Volume Management

❑	LVM is based on physical volumes, logical volumes, and volume groups.
❑	You can create and add LVM systems with a wide variety of commands starting with pv*, lv*, and vg*.
❑	The GUI LVM tool is an alternative for those who don't remember all of the commands required to manage logical volumes.