Certification Objective 1.13: Configuring External Devices

---

You can install many devices externally to your computer. These devices are sometimes known as peripherals. Generally, peripheral devices fall into five categories: serial, parallel, USB, IEEE 1394, and PC Cards. A device attached to a serial port, such as a mouse or a modem, uses the device associated with that port. Devices attached to parallel, USB, or IEEE 1394 ports normally use their own device files. PC Cards are a special case normally associated with laptop computers.

While Linux normally recognizes basic devices attached to serial or USB ports, such as a mouse during installation, configuring other devices may take additional work.

Serial Ports

In many cases, configuring a device for a serial port is as simple as linking to the driver of the associated port. For example, if you have an external modem connected to the only serial port on your computer, the Linux plug and play subsystem may have already linked the device for that port with the device for your modem. Run the ls -l /dev/modem command. If it shows something like the following output, you know that Linux has already linked your modem driver with the second serial port:

lrwxrwxrwx   1 root   root    10 Apr 4 11:28 /dev/modem -> /dev/ttyS1

Otherwise, you can use the ln command to create a link to the appropriate port. If you have a serial mouse, you should find the same type of link from /dev/mouse.

Parallel Ports

Configuring devices attached to a parallel port can be more complex. For example, Linux doesn't always recognize plug and play printers that are attached to a parallel port such as /dev/lp0. Further configuration with tools such as the CUPS Web-based tool or the Red Hat Printer Configuration tool may be required. You can find the device associated with your CUPS printer in the /etc/cups/printers.conf file.

If you're connecting an external hard drive to a parallel port, you'll want to install the paride module and the module associated with your device, whether it is a hard drive, a tape drive, or a CD-ROM. Similar steps are required for other parallel port devices. Detailed information on configuring parallel port devices is available from the Linux Parallel Port Web site at www.torque.net/linux-pp.html.

USB

Linux support for USB is growing with the evolution of the latest kernels. While the latest versions of Red Hat Enterprise Linux supports USB hot-swapping, support for the higher-speed USB 2.0 standard is still 'experimental,' as are Linux drivers for many USB devices. For the latest information, see the Linux USB Web site at www.linux-usb.org. You may be able to download your driver and install it using the techniques discussed in Chapter 4.

IEEE 1394

The Institute of Electrical and Electronics Engineers (IEEE) has developed the IEEE 1394 specifications for very high speed data transfer applications, such as digital movies. Equipment designed to these standards is often known by its trade names: FireWire and iLink. The current status is similar to USB; in other words, some IEEE 1394 equipment works with Linux, and development continues. For the latest information, see the Linux IEEE 1394 Web site at linux1394.sourceforge.net/hcl.php.

PC Card (PCMCIA)

Linux has one package called Card Services that deals exclusively with PC cards. This package includes all the kernel modules you'll need to manage PCMCIA cards and a set of drivers for specific cards. The package also includes a daemon that handles hot-swapping for most PC cards.

While development of the Card Services package is ongoing, there is often a period where there is no support for the proprietary configurations especially common on laptops. For this reason, the latest laptop is often not the best choice for a Linux installation. However, support for Linux on most name brand laptops is now common even when the laptop is first released. In fact, several companies sell laptops with Linux installed.

Supported PCMCIA Controllers

According to the Linux PCMCIA Information page at pcmcia-cs.sourceforge.net, Linux now supports all common PCMCIA controllers. If you have a problem with a specific PCMCIA card, focus on finding a driver for the card itself. A current list of supported PCMCIA controllers can be found on the Hardware HOWTO.

Supported Cards

The Card Services package comes bundled with a file named SUPPORTED.CARDS. You can probably find it on your Linux computer with the locate SUPPORTED.CARDS command. Also, you can check the PCMCIA HOWTO or the Red Hat Hardware Compatibility List for supported cards. Alternatively, the Linux PCMCIA Information Page may also be helpful.

On The Job 

During your career as a computer professional, there will be times you'll be asked to research a specific product or technology. To get an idea of how hard or easy this can be, call a major computer retailer or manufacturer and inquire about their latest laptop. Ask them if it supports Linux. What kind of answer do you get? Ask them if they have any earlier models that will. Do you believe the answers you receive are reliable? Check out the company's Web page, if you can, and find out if they provide any information about the product on the Internet. Doing this kind of research can be very trying, with or without success. Before deciding what kind of hardware you want to install Linux on, you should have a good understanding of what will and will not work. Start early and build a good base of reliable references you can use to find out new computer information. Web sites, such as the Linux Documentation Project, as well as magazines like Linux Journal, Linux Format (UK), Sys Admin Magazine, and Linux Magazine, will help you stay informed.

---