Differences between Linux and UNIX

In fact, looking at their development history, we will naturally know their differences. So the following shows their development history.

UNIX, Linux, and open source software

, At&t Bell Labs's kenth Thompson, Dennis Ritchie, and others began developing a small operating system on an older PDP-7. Soon after, the operating system was named UNIX, A puntion of a previous operating system project called multics. In 1972-1973, the system was rewritten in the C language. This is an extraordinary move: this decision makes UNIX The first widely used operating system that can be separated from its original hardware. Other new methods are also constantly added to Unix, partly because of the good collaboration between Bell Labs and academia. In 1979, the seventh version of Unix (V7) was released. It is the originator of all existing UNIX systems.

Since then, the history of Unix has become complicated. Researchers led by Berkeley developed variants known as the Berkeley Software release (BSD), while at&t continued to develop UNIX in the name of system III and subsequent System V. From the late 1980s s to the early 1990s S, the "war" between the two main branches intensified. After years of development, each variant has adopted many key features of other variants. In business, System V won the "standard war" (putting most of its interfaces into formal standards), and most hardware vendors switch to at&t's system v. However, System V involves many BSD innovations, making the system more like a fusion of two major branches. The BSD branch does not disappear, but is widely used on research, PC hardware, and single-purpose servers (for example, many web sites use a BSD variant ).

The final result is that many different versions of UNIX come from the original version 7. Most versions of UNIX are private and maintained by corresponding hardware vendors. For example, sun's Solaris is a variant of System V. Three versions of the unix bsd branch become open source software: FreeBSD (focus on simple installation on PC-type hardware), NetBSD (focus on a lot of different CPU Structures) openBSD, a variant of NetBSD, focuses on security ). More general information can be found on the http://www.datametrics.com/tech/unix/uxhistry/brf-hist.htm. More information about BSD history can be found on [mckusick 1999] And ftp://ftp.freebsd.org/pub/FreeBSD/FreeBSD-current/src/share/misc/bsd-family-tree.

If you are interested in the current use of Unix-like systems to defend against comments can look at the http://www.unix-vs-nt.org.

Free Software Foundation

In 1984, Richard Stallman's FSF launched the GNU program to create a free version of a UNIX operating system. Stallman indicates that the software can be freely used, read, modified, and re-released. FSF has successfully created many useful software, including a C compiler (GCC), an impressive Text Editor (Emacs), and a large number of basic tool software. However, in 1990s, FSF encountered troubles in developing the operating system kernel [FSF 1998]. Without the kernel, other software could not be used.

Linux

In 1991, Linus Torvalds began to develop an operating system kernel called "Linux" [Torvalds 1999]. This kernel can be combined with FSF data and other software (especially some BSD software and MIT's X-Windows software) to form an operating system that can be freely modified and very useful. In this article, the kernel itself is called the "Linux kernel", and the complete combination is called the "Linux ". Note: many people use the term "GNU/Linux" to refer to this combination.

In the Linux community, different organizations combine available software in different ways. Each combination is called a "release", and the organization that develops the release is called a "publisher ". General releases include red hat, Mandrake, Suse, Caldera, Corel, and Debian. There are differences between various releases, but all releases are based on the same foundation: Linux kernel and GNU glibc library. Because both of them are protected by the Copyleft type license, modifications to them must also be made to everyone, which is a unified force between BSD and at&t's UNIX system, make Different Linux distributions on the same basis. This article does not target any specific release. However, we assume that the Linux kernel version is 2.2 or later and the C library is glibc 2.1 or later, basically, this assumption applies to all major Linux distributions.

Open source software

The increasing interest in "free software" makes it increasingly necessary to define and interpret it. A widely used term "Open Source Software" is further defined in [OSI 1999. Eric Raymond [1997,199] has written several important articles on his development process. Another widely used term is "Free Software". "freedom" is generally interpreted as "freedom of speech, not free beer ". These two terms are not perfect. The term "Free Software" is often confused with programs that provide executable files free of charge but are not allowed to browse, modify, or resend source code. In contrast, the term "open source" is sometimes misused on software that can be browsed by source code but has restrictions on use, modification, or redistribution. This article uses the term "Open Source", which means that the source code of the software can be freely used, browsed, modified, or re-distributed. Interested in reading Open Source Software defense comments readers can look at the http://www.opensource.org and http://www.fsf.org.

Comparison between Linux and UNIX

This document uses the term "Unix-like" to describe Unix-like systems. In particular, the term "Unix-like" contains all major UNIX variants and Linux releases.

Linux is not the source code of UNIX, but its interface is intentionally designed to be Unix-like. Therefore, the lessons learned from UNIX can be applied in both aspects, including security information. Most of the information in this article can be applied to any UNIX-like system, but some specific Linux information is specially added so that Linux users can take advantage of the Linux performance.

Unix-like systems share many security mechanisms, although slightly different, and not all systems support all mechanisms. All the mechanisms here include the user and group ID (UID and GID) of each process and the file system with read, write, and execution permission (for users, groups, and others. See Thompson [1974] And Bach [1986] for general information about Unix systems, including their basic security mechanisms. Chapter 3 summarizes the key security mechanisms of UNIX and Linux.