LILO can boot a kernel image from several locations, such as a regular file on the root filesystem or any other mounted filesystem, a block device such as a floppy disk, or the boot sector of another partition or disk. The type of boot is dictated by entries in a configuration file. Boot image configuration files can have several variables defined, all of which have been mentioned in the preceding sections. Valid configuration file variables include alias, label, optional, password, ramdisk, read-only, read-write, restricted, root, and vga.

To boot a kernel image from a file, all that is necessary in the configuration file is the name of the image. For example, the line

image=/linux_main

boots the image called linux_main.

To boot an image from another device, the sectors that must be read on that device have to be specified. Several methods of providing the sector information exist. The starting sector must be provided, but you can then either specify a number of sectors to be read (start+length) or the end sector number (start-finish). If only one number is provided (the start sector), only that sector is read.

For example, the contents of this configuration file

image=/dev/fd0

range=1+512

will boot the kernel from the floppy disk, starting at sector 1 and reading the next 512 sectors.

You can specify more than one configuration for an image because LILO stores values in an image descriptor file and not in the image itself. For example, a configuration file can contain the following entries:

image=/linux_main

label=linux-hda1

root=/dev/hda1

image=/linux_main

label=linux-hda3

root=/dev/hda3

image=/linux_main

label=linux-flop

root=/dev/fd0

This code has three configurations for the same Linux kernel (linux_main), but it also has different root devices with three different alternate names. The boot devices for the image are /dev/hda1, /dev/hda3, and /dev/fd0 respectively. Whitespace in the configuration file is ignored, so the indentations are for ease of reading only.

Although Linux can run completely from a floppy disk with no hard disk, running it this way doesn’t offer a useful environment. Linux is designed primarily for hard disk use, and supports all the common hard disk controller systems including IDE (Integrated Drive Electronics), EIDE (Extended Integrated Drive Electronics), ESDI (Enhanced Small Device Interface), RLL (Run Length Limited), and SCSI (Small Computer System Interface). Linux supports the older 8-bit original PC controllers, although most controllers are 16-bit AT designs.

Linux is not choosy about the manufacturer and type of hard disk. As a rule, if DOS can handle the drive, so can Linux. This rule applies to all drives except SCSI drives, which require special handling. Linux still is restricted by most PC BIOS versions that impose limitations on the number of sectors, heads, and cylinders, however. There is an effective 1,024M size limit on drives with some older versions of Linux, and even some smaller drives can’t be handled properly by Linux or DOS because of the BIOS. More recent versions of the operating system can overcome some of these limitations. The version of Linux on the CD-ROM accompanying this book, for example, can use disk space over the 1G limit.

Linux supports most standard SCSI devices, but not all of the many different SCSI controllers and protocols on the market work well with Linux. Linux does support the most common SCSI controllers, though. Some other controllers are supported with enhanced BIOS chips on the PC motherboard. A size limitation on the SCSI drives is still imposed by the BIOS of many early versions of Linux, so a 2G drive will only have 1G available to Linux and DOS. Other UNIX systems, like SCO UNIX, can use the rest of the drive. Later versions of Linux (mostly any kernel from version 1.1 and on) can use more than 1G of disk space on SCSI drives.

The size of disk space required by Linux depends on the parts of the operating system that are installed. A minimum effective system is 20M, which gives enough room for the basic utilities but not X. To load the entire basic Linux system, including development tools and X, provide at least 150M just for the files. Then add whatever space is required for your personal files and temporary storage for Linux. A good rule of thumb is to double the space requirements. In addition to the user space, remember to leave room for the swap space. Although the swap space size depends on what the system is used for, a good number to use is 16M.

You can use more than one drive, although you should place a bootable root Linux partition on the first drive. You also must load DOS on the first drive, although you can place partitions on other drives. The number of drives supported depend on the drive controller and BIOS. IDE systems are usually limited to two drives, but EIDE systems can handle four drives (two drives off two controllers). ESDI and RLL controllers are usually limited to two drives. SCSI controllers can handle up to seven drives per controller, and a single system can contain several controllers. SCSI is the most versatile (and also the most expensive) system.

Because hard disks are now inexpensive, obtaining large-capacity drives is relatively easy. Linux can share a disk with up to three other operating systems (more with a few tricks), so if you plan to load DOS and Linux, for example, allocate enough drive space for both operating systems.

USENET is a collection of discussion groups (called newsgroups) available to Internet users. The over 13,000 newsgroups generate over 100M of traffic every day. Of all these newsgroups (which cover every conceivable topic), several are dedicated to Linux. These newsgroups are a useful forum for information and answers to questions about Linux.

You can read USENET newsgroups through newsreader software that accesses either the Internet or a local site that offers USENET service (called a newsfeed). Many on-line services, such as CompuServe and Delphi, provide access to the newsgroups (sometimes at an additional cost), and some have their own forums for Linux users. BBSs dedicated to Linux in whole or in part are also appearing, and many excerpt the USENET conversations for the BBS users who do not have access to USENET.

USENET newsgroups are divided into three categories: primary newsgroups that are readily available to all users, local newsgroups with a limited distribution (usually based on geography), and alternate newsgroups that may not be handled by all news servers due to the relaxed rules of etiquette on them. The primary newsgroups of interest to Linux users when this book was written are the following:

The comp.os.linux.admin newsgroup deals with administering Linux systems.

Proponents of the Linux system sound off in comp.os.linux.advocacy.

The comp.os.linux.announce newsgroup contains announcements important to the Linux community. This is a moderated newsgroup, which means someone approves the postings before you get to see them.

The comp.os.linux.answers newsgroup contains questions and answers to problems about Linux.

Ongoing work on Linux in general is discussed in comp.os.linux.development.

Ongoing work on Linux applications is discussed in comp.os.linux.development.apps.

Ongoing work on the Linux operating system is discussed in comp.os.linux.development.system.

The comp.os.linux.hardware newsgroup deals with issues concerning Linux and hardware support.

The comp.os.linux.help newsgroup contains questions and advice about Linux.

Linux-specific topics not covered by other groups are covered in comp.os.linux.misc.

Linux networking issues are discussed in comp.os.linux.networking.

The comp.os.linux.setup deals with Linux setup and installation problems.

These primary newsgroups should be available at all USENET sites unless the system administrator filters them out for some reason. The other Linux newsgroups tend to change frequently, primarily because they are either regional or populated with highly opinionated users. The alt (alternate) newsgroups are the ones most likely to contain such users. One alt newsgroup in operation when this book was written is

alt.uu.comp.os.linux.questions
To find the several different newsgroups about Linux, use your newsreader software to search for all newsgroups with the word linux in the title. If you have access to USENET, regularly scan the newsgroup additions and deletions to check for new Linux newsgroups or existing groups that have folded. Notices about newsgroup changes are usually posted to all existing groups, but every now and again one gets through without fanfare. On-line services that provide access to USENET usually maintain lists of all active newsgroups that can be searched quickly.

The traffic on most of these Linux newsgroups deal with problems and issues people have when installing, configuring, administering, or using the operating system. A lot of valuable information passes through the newsgroups quickly, so check them regularly. The most interesting messages that deal with a specific subject (called a thread) are often collected and stored as an archive for access through an FTP site.