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Understanding Kernel Configuration Options - Administration

Today, continue on your path to RHCE certification. Learn about creating a new kernel the easy way, kernel sources, recompiling a kernel, and the cron and at systems. Take notes, because there's a test at the end. This comes from chapter five of Red Hat Certified Engineer Linux Study Guide (Exam RH302), fourth edition, by Michael Jang. (McGraw-Hill/Osborne, 2004, ISBN: 0-07-225365-7).

TABLE OF CONTENTS:
  1. Kernel, Cron, and User Administration, Part 2
  2. Updating Your Boot Loader
  3. The Kernel Source Tree and Documentation
  4. The Kernel RPMs
  5. GUI Kernel Source Management
  6. The Linux Kernel tar File
  7. Understanding Kernel Configuration Options
  8. Compiling and Installing a Custom Kernel
  9. The cron and at Systems
  10. Setting Up cron for Users
  11. Certification Summary
  12. Self Test
  13. Lab Questions
  14. Self Test Answers
  15. Lab
By: McGraw-Hill/Osborne
Rating: starstarstarstarstar / 7
October 06, 2004

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To configure a kernel, you need to understand some of the main kernel configuration options. Each of the aforementioned kernel configuration tools includes help menus for just about every available option.

The Basic Kernel Configuration
If you’re asked to change a setting such as CONFIG_EXPERIMENTAL, you don’t have to search through different menus. You can find the governing menu using the information in the /boot/config-2.4.21-4.EL configuration file. As you can see in the file:

# Code maturity level options
#
CONFIG_EXPERIMENTAL=y

The CONFIG_EXPERIMENTAL variable can be found under the Code Maturity Level Options menu.

The Standard Red Hat Kernel Configuration
The standard RHEL 3 Linux kernel supports a wide variety of hardware and software. Almost every module that could be made is made. This is a big kernel, and numerous modules can be used for it with the standard installation. This is not a problem when you install RHEL 3, but it is highly recommended you streamline the standard kernel and remove unwanted modules.

In the following sections, I describe the different kernel configuration menus, section by section. However, since it appears that recompiling the kernel is no longer a requirement on the Red Hat exams, I do not provide any screenshots of additional menus. If you’re interested in this level of detail, follow along on your Red Hat computer.

Code Maturity Level Options
The Code Maturity Level options allow you to incorporate experimental code in the kernel. Common examples include drivers for new hardware, esoteric filesystems, and network protocols. Experimental code is often also known as alpha level software. If you have obsolete code that you want to incorporate into your kernel, it also falls in this category, as newer kernels often omit support for older features.

The one option relates to the CONFIG_EXPERIMENTAL variable. It’s enabled by default in RHEL 3.

Loadable Modules Support Options
The Loadable Module Support screen allows you to enable loadable modules. The kernel module loader will automatically load modules for most new hardware, when detected. As discussed earlier, loadable modules allow you to optimize the kernel. If you want to optimize the kernel, keep all of the options on this screen active.

Processor Type and Features
The Processor Type and Features menu in RHEL 3 supports a wide variety of CPUs.

General Setup Options The General Setup Options menu includes some basic hardware and kernel configuration options. Many of these options are self-explanatory, and the defaults are generally acceptable. If you need more information, click the Help button associated with a specific kernel option.

On a network, you want networking support. Most computers have PCI cards, and the defaults give you full PCI support, using BIOS detection, documenting the detected cards in the /proc directory. Various types of hot-pluggable devices are now popular, including PCMCIA cards for laptops and PCI hotplug support for removable drives.

The System V IPC, BSD Process Accounting, and Sysctrl support parameters are all standard for current kernels. While Linux kernels are normally associated with ELF binaries, the other binaries may help with certain programs.

Memory Technology Devices
The options shown in the Memory Technology Devices menu allow you to set up Linux for basic “Flash” memory cards, including those that might be installed through a PCMCIA adapter. Unless you’re planning to use some of these devices in the future, keep this option disabled.

Parallel Port Support
The options shown in the Parallel Port support menu are based on hardware that may be connected to your computer through a parallel port. This includes everything from printers through parallel port hard drives. Remember that it is normally best to avoid the Experimental options unless you are a developer working on supporting the associated drivers.

Plug and Play Configuration
The options shown under the Plug and Play Configuration menu activate basic plug and play support on your Linux computer. Generally, you should keep the defaults. While Linux plug and play does not handle all ISA and PCI devices, it does help you configure your computer for Linux.

Block Device Options
Under the Block Device Options menu, you can specify your floppy devices and nonstandard hard disks. You can specify support for parallel port ATAPI CD-ROMs, tape drives, and even ATAPI floppy drives. You can also enable loopback support and network block support (which lets you use a physical disk on the network as if it were a local disk). If you have any parallel port devices such as external CD-ROMs or hard drives, you could enable support for those here. You can also set up support for RAM disks under this menu.

Multidevice Support for RAID and LVM
If you’re ever going to set up a RAID array of disks to help protect your data, you can enable that option in the Linux kernel under the Multidevice Support for RAID and LVM menu. If you ever want to put together a volume set, where a directory can span more than one partition on more than one physical hard disk, you can enable that option here as well.

ON THE JOB!  While there is support for RAID-4 in the Linux kernel, it is not directly supported by RHEL 3 or currently available versions of Red Hat or Fedora Linux.

Networking Options
There are many options for networking in the Linux kernel. The Networking Options menu is extensive. It includes a substantial number of settings for different hardware devices, software settings, and more.

Telephony Support
Telephony support on a computer network uses special network cards to convert voice into the type of data that can be sent over a network. Linux offers some limited telephony support through the kernel as shown under the menu of the same name.

ATA/IDE/MFM/RLL Support
These acronyms all relate to various types of regular PC hard disk and CD drive interfaces. Normally, you shouldn’t disable this kernel option unless all hard disk storage on your system is based on a SCSI interface. Even then, the flexibility of being able to install IDE devices is usually worth the extra code this adds to the kernel.

SCSI Support Options and Low-Level Drivers
You can enable SCSI hard disks, tape drivers, and CD-ROM support in this section. If you have a SCSI CD-ROM jukebox, or any other device that requires more than one SCSI Logical Unit Number (LUN), you may have to enable probing of all LUNs.

Near the bottom of the menu, you can configure verbose SCSI error reporting. You can also enable specific low-level SCSI support. Red Hat includes support for high-end hardware RAID-enabled SCSI host adapters, including 64-bit PCI adapters.

Fusion MPT Device Support
This menu supports modules associated with very high speed SCSI adapters, associated with hardware developed by LSI logic.

IEEE 1394 Support
The IEEE 1394 standard is more popularly known as FireWire or iLink. It’s basically a very high speed hot plug and play hardware option, with data transfer speeds in the hundreds of Mbps. Linux support for IEEE 1394 standards is far from complete. Kernel support for any IEEE 1394 device is currently officially experimental. However, support for IEEE devices such as external hard drives are readily available, and configured as modules by default in RHEL 3.

I2O Device Support
The I2O specification, also known as Intelligent I/O, supports split drivers which can optimize communication performance between a device and the rest of your computer. Don’t enable I2O haphazardly; it requires hardware that supports it.

Network Device Support
Linux supports a wide range of network cards. The Network Device Support menu allows you to enable support for the adapters you may need. Generally, you should enable support for only network devices that you’re using now or may use in the future.

Amateur Radio Support
Linux supports connections to various amateur radios. Unless you plan to connect your computer to an amateur radio station in the future, there is no need to enable support for any of these devices.

IrDA Support
Linux supports Infrared connections, mostly for network support. The IrLAN protocol supports wireless access points. The IrNET protocol requires PPP. The IrCOMM protocol sets up port emulation, useful for setting up terminals and printers. For a list of supported infrared-port device drivers, click that button and activate the devices that you need.

ISDN Options
Integrated Services Digital Networks (ISDN) lines are a fairly popular high-speed digital option, especially outside of North America. Adding ISDN support allows you to use an ISDN card for inbound or outbound dialing connections. The ISDN device has a built-in AT-compatible modem emulator, autodial, channel-bundling, callback, and caller authentication without the need for an external daemon to be running. Under the ISDN Options menu, you can enable synchronous Point-to-Point Protocol (PPP) connections. The supporting isdn4k-utils RPM is installed by default on RHEL 3.

Older CD-ROM Support Options
If you have an older CD-ROM that is not an IDE or SCSI CD-ROM, then you need to enable special support for it in the Linux kernel, as shown when you click the “Old CD-ROM drivers (not SCSI, not IDE)” option. This section has many drivers for Mitsumi, Goldstar, Philips, Sony, Sound Blaster, and other old CD-ROM and disk types.

Input Core Support
The Input Core Support section configures support for various basic input devices: keyboards, mice, and joysticks. These devices are modular by default, which allows Linux to recognize these basic devices using plug and play detection.

Character Device Options
Character devices send their data in byte streams. Typical character devices range from serial ports to virtual consoles. The Character Devices submenu allows you to specify support for a wide variety of devices, including virtual terminals, serial ports, newer AGP video cards, mice, joysticks, non-SCSI tape drives, and more.

Multimedia Devices
The Multimedia Devices options support a wide range of video capture and AM/FM radio devices. Click each option (Video for Linux, Radio Adapters) for a list of drivers which you can enable. As always, it is best to keep what you enable to a minimum.

Filesystem Options
The File Systems subsection is a list of all the different types of filesystems Linux supports. Select the Quota option if you need to support quotas. You can also compile in the kernel Automounter to support remote filesystems.

Because Linux supports so many different hardware platforms, it includes support for a large number of filesystem types. However, because of the proprietary nature of some filesystems, the degree of support is variable. You’ll note that support for a lot of filesystems in this menu is experimental; in fact, support for writing to NTFS filesystems may be dangerous!

Console Driver Options
Linux supports console drivers, which can set up text on most graphics systems, even when Linux doesn’t detect the right cards or monitors. The Frame Buffer Support option supports video adapters that store images in frame buffers.

Sound System Support Options
A wide variety of sound cards are supported by RHEL 3, normally as modules. These cards range from the Ensoniq Audio PCI card to TV card mixers. You can also use these drivers for cards that emulate the appropriate hardware. Check the Sound submenu for the latest list of supported hardware for your kernel. If you have a card not named in the previous list, try to see if it emulates any card on the list. Many proprietary cards do emulate products from Sound Blaster or offer OPL/2 or OPL/3 compatibility.

USB Support
Linux supports a number of USB mass storage devices, input devices, printers, cameras and scanners, and even modems. Linux support for USB networking cards is still officially experimental. Linux support for USB is improving, although some USB drivers that you’ll see in the USB support menu are still considered experimental as well. Unfortunately, this includes support for faster USB 2.0 standard drivers.

Additional Device Driver Support
As befits the name, the Additional Device Driver support menu allows you to configure the Linux kernel for a variety of hardware devices. These devices range from Gigabit Ethernet adapters to Storage Area Network devices.

Bluetooth Support
Bluetooth is a radio technology for short-range networks. You can configure a number of Bluetooth devices in the Linux kernel.

Profiling Support
Profiling support allows you to use the OProfile system to characterize the performance of your system. It is described in more detail at oprofile.sourceforge.net.

Kernel Hacking
Kernel hacking allows you to use the drivers you need to debug driver or related Linux kernel issues.

Cryptographic Options
The Cryptographic options support software associated with strong encryption in Linux. It’s disabled by default in RHEL 3.

Library Routines
The Library Routines support compression in Linux. Unlike for Red Hat Linux 9, they are enabled by default for RHEL 3.

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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