UNIX System Administration Handbook - Evi Nemeth [13]
The most recent major development in the UNIX world has been the advent of the Linux kernel and the many UNIX systems that are now based upon it. Linux is a soup-to-nuts reimplementation of the UNIX kernel that was begun in 1991 as a personal project of Linus Torvalds, a Finnish graduate student. Over the years, the Linux project accumulated many developers, users, and enthusiasts. It has grown into a full-featured, production-quality kernel that many vendors support as their primary operating system. Many big-ticket commercial software packages (such as Oracle) have also been ported to Linux.
1.3 EXAMPLE UNIX SYSTEMS
In this book, we have chosen four popular UNIX variants as our examples: Solaris 2.7, HP-UX 11.00, Red Hat Linux 6.2, and FreeBSD 3.4. These systems are representative of the overall UNIX marketplace, and they’re all so common that it’s hard to find a UNIX site that doesn’t use at least one of them.
Sun Microsystems’ Solaris is a System V derivative with many extensions. Sun UNIX (yes, that’s what it was called in the mid-80s) was originally the progeny of Berkeley UNIX, but a (now historic) corporate partnership between Sun and AT&T forced a change of platform.
HP’s HP-UX is a hybrid of the System V and Berkeley UNIX trees, but with odd surprises of its own.
Several free UNIX systems are available for Intel hardware, and of these Linux is currently the most popular.1
Linux itself is just a kernel; you must add on a full complement
of commands, utilities, and daemons to form a complete UNIX system. The various Linux “distributions” bundle the kernel with the other components needed for a full installation. Linux distributors make many choices while assembling their products, so versions of Linux can be quite different from one another. A few companies (including Red Hat, SuSE, and Corel) provide production-grade distributions with full support.
FreeBSD is a system based on Berkeley’s 4.4BSD-Lite release. Like Linux, it runs on a variety of Intel platforms. A commercially supported version is available from BSDI.
1.4 NOTATION AND TYPOGRAPHICAL CONVENTIONS
In this book, filenames, commands, and literal arguments to commands are shown in boldface. Placeholders (e.g., command arguments that should not be taken literally) are in italics. For example, in the command
cp file directory
you’re supposed to replace file and directory with the names of an actual file and an actual directory.
Excerpts from configuration files and terminal sessions are shown in a fixed-width font.2 Sometimes, we annotate interactive sessions with italic text. For example:
% grep Bob /pub/phonelist /* Look up Bob's phone # */
Bob Knowles 555-2834
Bob Smith 555-2311
Outside of these specific cases, we have tried to keep special fonts and formatting conventions to a minimum so long as we could do so without compromising intelligibility. For example, we often talk about entities such as the UNIX group daemon and the printer anchor-lw with no special formatting at all.
In general, we use the same conventions as the UNIX manual pages for indicating the syntax of commands:
• Anything between square brackets (“[” and “]”) is optional.
• Anything followed by an ellipsis (“...”) can be repeated.
• Curly braces (“{” and “}”) indicate that you should select one of the items separated by vertical bars (“|”).
For example, the specification
bork [-x] {on|off} filename ...
would match any of the following commands:
bork on /etc/passwd
bork -x off /etc/passwd /etc/termcap
bork off /usr/lib/tmac
We use shell-style globbing characters for pattern matching:
• A star (*) matches zero or more characters.
• A question mark (?) matches one character.
• A tilde or “twiddle” (~) means the home directory of the current user.
• ~user means the home directory of user.
For example, we sometimes refer to the BSD startup scripts /etc/rc, /etc/rc.boot, and /etc/rc.local with the shorthand pattern /etc/rc*.
Text within quotation marks often has a precise technical meaning. In