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2-1 lists IRQ and DMA channels used by various "standard" devices found on most systems. Almost all systems have some of these devices, so you should avoid setting the IRQ or DMA of other devices to these values.

Table 2-1. Common device settings

Device

I/O address

IRQ

DMA

ttyS0 (COM1)

3f8

4

n/a

ttyS1 (COM2)

2f8

3

n/a

ttyS2 (COM3)

3e8

4

n/a

ttyS3 (COM4)

2e8

3

n/a

lp0 (LPT1)

378 - 37f

7

n/a

lp1 (LPT2)

278 - 27f

5

n/a

fd0, fd1 (floppies 1 and 2)

3f0 - 3f7

6

2

fd2, fd3 (floppies 3 and 4)

370 - 377

10

3

Problems recognizing hard drive or controller

When Linux boots, you see a series of messages on your screen, such as the following:

Console: switching to colour frame buffer device 147x55

Real Time Clock Driver v1.12

Serial: 8250/16550 driver $Revision: 1.1 $ 48 ports, IRQ sharing enabled

ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A

Using anticipatory io scheduler

Floppy drive(s): fd0 is 1.44M

FDC 0 is a post-1991 82077

...

Here, the kernel is detecting the various hardware devices present on your system. At some point, you should see a line like the following:

hda: hda1 hda2 hda3 hda4 < hda5 hda6 hda7 >

If, for some reason, your drives or partitions are not recognized, you will not be able to access them in any way.

Several conditions can cause this to happen:

Hard drive or controller not supported

If you are using a hard drive or controller (IDE, SCSI, or otherwise) not supported by Linux, the kernel will not recognize your partitions at boot time.

Drive or controller improperly configured

Even if your controller is supported by Linux, it may not be configured correctly. (This is a problem particularly for SCSI controllers ; most non-SCSI controllers should work fine without additional configuration.)

Refer to the documentation for your hard drive and controller for information on solving these kinds of problems. In particular, many hard drives will need to have a jumper set if they are to be used as a slave drive (e.g., as the second hard drive). The acid test for this kind of condition is to boot up Windows or some other operating system known to work with your drive and controller. If you can access the drive and controller from another operating system, the problem is not with your hardware configuration.

See the previous section, "Isolating hardware problems," for information on resolving possible device conflicts and the following section, "Problems with SCSI controllers and devices," for information on configuring SCSI devices.

Controller properly configured, but not detected

Some BIOS-less SCSI controllers require the user to specify information about the controller at boot time. The following section, "Problems with SCSI controllers and devices," describes how to force hardware detection for these controllers.

Hard drive geometry not recognized

Some older systems, such as the IBM PS/ValuePoint, do not store hard drive geometry information in the CMOS memory where Linux expects to find it. Also, certain SCSI controllers need to be told where to find drive geometry in order for Linux to recognize the layout of your drive.

Most distributions provide a boot option to specify the drive geometry. In general, when booting the installation medium, you can specify the drive geometry at the LILO boot prompt with a command such as:

boot: linux hd=cylinders

,heads

,sectors

where cylinders, heads, and sectors correspond to the number of cylinders, heads, and sectors per track for your hard drive.

After installing the Linux software, you can install LILO, allowing you to boot from the hard drive. At that time, you can specify the drive geometry to the LILO installation procedure, making it unnecessary to enter the drive geometry each time you boot. See "Using GRUB" in Chapter 17 for more about LILO.

Problems with SCSI controllers and devices

Presented here are some of the most common problems with SCSI controllers