Certification Objective 1.12: Hardware Compatibility

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Now it's time to explore in detail the hardware that Red Hat Enterprise Linux can handle. While some manufacturers now include their own Linux hardware drivers, most Linux hardware support comes from third parties. Fortunately, there is a vast community of Linux users, many of whom produce drivers for Linux and distribute them freely on the Internet. If a certain piece of hardware is popular, you can be certain that Linux support for that piece of hardware will pop up somewhere on the Internet and will be incorporated into various Linux distributions, including Red Hat Enterprise Linux.

Be careful when purchasing a new computer to use with Linux. Though Linux has come a long way the last few years, and you should have little problem installing it on most modern PCs, you shouldn't assume Linux will run on any PC, especially if the PC in question is a state-of-the-art laptop computer. Laptops are often designed with proprietary configurations that work with Linux only after some reverse engineering.

Fortunately, there are a number of major manufacturers who support RHEL 3 out of the box for their workstations and servers. Check the Red Hat Hardware Compatibility List, as discussed in the section of the same name, for the latest information.

Other kinds of hardware, such as 'winmodems' and 'winprinters,' are designed to use Microsoft Windows driver libraries. Integrated hardware (such as video chips that share system RAM) and parallel port devices can also be problematic. While Linux drivers exist for many of these devices, do your research.

Linux runs very well on lower-end computers. This is one of Linux's strong points over other operating systems, such as Microsoft's Windows XP. Linux runs fine on 64MB of RAM, although more is always better, especially if you want to run any graphical applications.

On The Job 

While it is important to know how to select and configure hardware components to get to a smoothly running Linux computer, the RHCE exam is not a hardware exam.

Linux Hardware Documentation

There are many resources available to help you select the best hardware for Linux. Thousands of Linux gurus are available online in areas such as mailing lists and newsgroups. Perhaps the best places to look are the Linux Documentation Project (LDP) or the Red Hat Hardware Compatibility List. The LDP is a global effort to produce reliable documentation for all aspects of the Linux operating system, including hardware compatibility.

Linux Hardware HOWTO

The Linux Hardware HOWTO is a document listing most of the hardware components supported by Linux. It's updated irregularly with added hardware support, so it is a relatively up-to-date source of information. As of this writing, various LDP HOWTOs are supplied on the documentation CD-ROM in text format and in various languages, in the /HOWTOS directory. The official up-to-date list can be found at the LDP www.tldp.org.

The Red Hat Hardware Compatibility List

The Red Hat Hardware Compatibility List is different from the one you'll find in the Linux Hardware HOWTO. It specifies name brand hardware that has been tested with RHEL and Red Hat Linux (versions 9 and below). If you've purchased RHEL 3, Red Hat will provide some level of installation support for any certified or compatible hardware. Some hardware that has been tested by Red Hat has specifically been found not to work with Red Hat Linux or RHEL and is therefore not supported. Red Hat hasn't tested all PC hardware; as a courtesy, they also include a list of hardware that others have tested with Red Hat Enterprise Linux, as 'Community Knowledge' hardware. These four categories of hardware are described in Table 1-8.

Table 1-8: Red Hat Hardware Compatibility Categories




Approved by Red Hat, Inc., through the Red Hat Hardware Certification Program.


Reviewed by Red Hat, and known to be supported.

Not Supported

Reviewed by Red Hat, and known not to work with Red Hat Linux or RHEL.

Community Knowledge

Untested by Red Hat; others have reported some degree of compatibility with Red Hat Linux and RHEL.

Like the Linux Hardware HOWTO, the Red Hat Hardware Compatibility List draws upon the efforts of volunteers. If you want to check if any of the 'latest' hardware (such as USB) will run on your Linux system, it's probably best to consult the Red Hat support site first, then maybe LDP's Linux Hardware HOWTO. However, if you want the option of being able to contact Red Hat for support, you should stay within the 'supported' list of the Red Hat Hardware Compatibility List.

Check the documentation for your hardware. Find a component such as a modem or a network card. Cross-check this component against the Red Hat and LDP hardware compatibility lists (HCLs). Find the Red Hat lists by starting at www.redhat.com. Find their HCL in their support area. Find the LDP Hardware HOWTO by starting at www.tldp.org. Find this list in the LDP section on HOWTOs. Compare the results. While in most cases the results are identical, it's good to know how to search through both sources just in case.

As part of this process, find a component listed on one or both of these HCLs as incompatible with Linux. Do a search on your favorite search engine or the newsgroups based on the name and model of the product. Don't forget to include 'linux' in your list of search terms. You might be pleasantly surprised. As of this writing, a searchable newsgroup database is available at groups.google.com.

CPU and SMP Support

Red Hat Enterprise Linux for Intel supports computers with Intel and compatible processors. It is 'Itanium-ready,' which means that it will be able to support this 64-bit Intel CPU when it is finally released.

Linux is commonly used as a server operating system. Many server applications can take advantage of the flexibility provided by multiple CPUs. This is known as symmetric multiprocessing (SMP) support. Linux began supporting multiple CPUs with the release of the 2.4 kernel back in 2001.

On The Job 

Some of the developers hope to increase the SMP limit to 128 CPUs. If you're running Linux on a SMP computer, keep up to date with the latest kernel developments at www.kernel.org.

Exam Watch 

Red Hat Enterprise Linux was released with Linux Kernel version 2.4.21. While it includes a number of features, or 'backports,' from Linux Kernel 2.6, I don't believe that you'll need to install the 2.6 kernel for the RHCE or RHCT exams. As always, monitor the Red Hat syllabus and requirements for the latest information.

Plug and Play

Plug and play (PnP) refers to the capability of an operating system to automatically allocate hardware ports or addresses to specific devices such as hard drives, sound cards, or modems. Linux's ability to work with plug and play devices is somewhat less than perfect. For example, if you have the right network modules installed with the kernel, Linux may be able to automatically detect and install the drivers for a new network card in a PCMCIA slot. However, Linux does not automatically detect all printers; in this case, you may need to use the techniques discussed in Chapter 8 to install the appropriate print driver.

A plug and play system has three parts: the BIOS, the device, and the operating system. Unless all three work perfectly, problems can arise with plug and play. The BIOS has to allow the operating system to find the devices on your computer. Plug and play devices have to accept port and channel assignments from the operating system. And a plug and play operating system is constantly searching each connection for new hardware. Red Hat developed the kudzu utility to look for and configure any hardware changes when you boot Linux.

Plug and Play Support in Linux

The unfortunate truth is that Linux doesn't handle plug and play as well as we may want. The main problem lies with plug and play support for devices that run on an ISA bus. ISA is a legacy technology from older IBM PCs, created without plug and play in mind, so support for it is complex.

PCI hardware is a different story. As Linux loads, device drivers can easily find PCI devices. However, conflicts may still arise with ISA devices. While Linux works well with many USB and IEEE 1394 devices, support for the latest USB 2.0 and IEEE 1394 hardware is still officially 'experimental' as of this writing.

Plug and Play Conflicts

The Linux plug and play subsystem may have problems with the newest computer devices or some very old ones. If you're having problems with the newest computer equipment, various Web sites are dedicated to offering help. For example, www.linmodems.org can help you configure many so-called 'winmodems,' and www.linux-usb.org can help you configure the latest USB equipment on Linux.

Many hardware conflicts with relatively old equipment are fairly simple to eliminate. There are three possible areas of conflict:

  • A physical hardware jumper is conflicting with another card.

  • Your ISA plug and play cards are not properly configured.

  • You are out of IRQs or other resources to add to your new device.

You can use the /proc files to check the currently used IRQ ports, I/O addresses, and DMA channels. For example, to check the occupied IRQs, the following command lists the devices that are loaded by the kernel:

# cat /proc/interrupts

If there is a conflict, the device is not loaded. You can quickly scan over the left side to see what interrupts are available. To get a list of used I/O addresses and DMA channels, issue the following commands:

# cat /proc/ioports # cat /proc/dma

The kernel included with Red Hat Enterprise Linux 3 and above should keep plug and play configuration problems to a minimum. When problems arise, two or more devices are probably trying to use the same IRQ, I/O, and/or DMA. In that case, one or both devices may not be loaded. It may take a little detective work to identify the troubled hardware; conflicts may prevent it from being listed in one of the associated /proc directory files. Then select one of the devices, and change its IRQ, I/O, and/or DMA to a free location.

This is usually a two-step process: first, change the settings on the card itself through physical jumpers or a diagnostic disk, as described in the next section. If Linux doesn't detect your changes, use the appropriate configuration utility, such as redhat-config-mouse, ifconfig, modprobe, or redhat-config-network, to change the settings on your device.

Generally, Linux should not have problems with PCI plug and play cards or USB devices. Linux should recognize them and set them up with appropriate IRQ ports, I/O addresses, and DMA channels. If you cannot see what your PCI cards are set to, you can type cat /proc/pci. If a PCI card that you're concerned about does not show up here, you may be out of IRQs. If you run out of IRQs, you may want to look into alternatives such as IEEE 1394 (also known as FireWire or iLink) or USB devices.


Closely related to plug and play are the latest computer power management standards, known as Advanced Configuration and Power Interface (ACPI) and Advanced Power Management (APM). Both are efforts to manage PC power consumption. As such, they are important tools to extend the lifetime of battery-operated devices such as laptop computers.

Microsoft has driven developments in both areas toward computers that can be easily suspended and reactivated from a minimum power state. Red Hat has incorporated some ACPI features from the 2.6 kernel in RHEL.

If you have problems with an ACPI computer, you can deactivate ACPI support with the acpi=off command to the kernel during the Red Hat Enterprise Linux boot or installation process.

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RCHE Red Hat Certified Engineer Linux Study Guide[c] Exam (Rh302)
RCHE Red Hat Certified Engineer Linux Study Guide[c] Exam (Rh302)
ISBN: 71765654
Year: 2003
Pages: 194

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