Widely Used UNIX Variants


As mentioned before, there is no single operating UNIX operating system. Instead, there is a large collection of UNIX variants. All these variants share a large number of features. Furthermore, porting software between the widely used variants is relatively straightforward. Many of the differences between variants are hidden to the user, and other difference result from the way these variants have evolved. The most significant differences are in the areas of add-ons that help make particular UNIX variants well suited for particular purposes and tasks.

We will briefly describe some of the most important variants here. Subsequent chapters will address the common features shared by different variants of UNIX as well as some of their differences. They will also address some of the specific aspects of some of the most widely used UNIX variants, including Linux, Solaris, HP-UX, Mac OS X, and AIX.

Linux

Linux is an extremely popular variant of the UNIX System. Among the reasons for this popularity is that it can be used free of charge, as well as the depth and breadth of its capabilities and the large amount of software that runs on Linux, made possible by the expertise and dedication of the large Linux development community. This popularity has also been helped by the support for Linux by many commercial computer companies, including IBM, HP, Sun, and Novell. Linux is covered by a copyright under the terms of the GNU General Public License, which prevents people from selling it without allowing the buyer to freely copy and distribute it. The Linux kernel is available on the Internet at hundreds of FTP sites. Linux is now available for many different processors, including the Intel x86 family, Motorola 68k, Sparc, and Power PC.

Today, Linux is widely used both on the desktop and on servers, in the homes, small businesses, and enterprises. Although Linux is not compliant with the POSIX.1 standard, it exhibits a high degree of POSIX compliance. The goal of its developers is to make it as compliant as possible with standards from the Open Group. Linux shares many features of UNIX System V and has many enhancements. It has become a widely popular version of UNIX for use on personal computers. Several desktop environments, including GNOME and KDE, run on Linux, making it easy for users to use Linux if they are used to Windows PCs. Also, application software is readily available for Linux. In the past five years it has become widely used for server applications and is now extensively run on web servers, mail servers, file servers, and firewalls.

To begin using Linux, you will need to obtain a Linux distribution. (You can also buy a PC that is preconfigured with a Linux distribution.) A Linux distribution contains the Linux kernel, a collection of programs and applications that run on Linux, and an installation program. Linux distributions are available from commercial vendors, from nonprofit organizations, from teams of people, and from individuals. Linux distributions can be sold as long as they do not limit the redistribution of their software. There are many different Linux distributions (one count lists more than 450-see http://en.wikipedia.org/wiki/List_of_Linux_distributions). Some Linux distributions are general purpose for desktops or for servers, and some are designed for specific purposes ranging from embedded systems to real-time computing. Although most people speak of Linux as one single operating system, each distribution is really a separate operating system. That is, the many different Linux distributions are really distinct variants of UNIX.

Among the more popular general-purpose Linux distributions (available either via Internet downloading or on CD-ROM) are those from Red Hat (http://www.redhat.com/), Caldera (owned by the SCO Group) (http://www.caldera.com/), Debian (http://www.debian.org/), SuSE (now owned by Novell) (http://www.novell.com/linux/suse/), Mandriva (http://www.mandriva.com/), TurboLinux (http://www.turbolinux.org/), and Slackware (http://www.slackware.org/). Sometimes, vendors of Linux distributions offer a free version of their distribution via Internet download and also sell their distribution on media and with support. Linux distributions may vary in many ways, including the version of the Linux kernel, the programs they include along with the kernel, and their installation programs. Among the applications included with many Linux distributions are web browsers, the Apache web server, security tools, and office applications such as Open Office, a complete office suite. Because of the differences between Linux distributions, applications that run on one distribution may not run on a different distribution. To remedy potential incompatibilities, an effort is underway called the Linux Standard Base (LSB) to develop and promote standards that will increase compatibility among Linux distributions with the goal that applications will be able to run on any compliant Linux system. To learn more about the LSB, go to http://www.linuxbase.org/.

Most of the material in this book is relevant for Linux users, and special attention has been taken to explain some of the most important variations found in Linux. A good starting place for more information about Linux is http://www.linuxresources.com/.

BSD Variants: FreeBSD, NetBSD, and OpenBSD

The Berkeley Software Distribution has been used a base for the development for several widely used UNIX variants, including FreeBSD, NetBSD, and OpenBSD. Surveys show that among users of variants of BSD, FreeBSD is by far the most commonly used, followed by OpenBSD, and then NetBSD.

FreeBSD

FreeBSD 1.0 was introduced in 1993. It was originally based on 4.3BSD-Lite and 386BSD, with many GNU components. Because of legal concerns regarding 386BSD source code, FreeBSD 2.0, released in 1994, was based on 4.4BSD-Lite. FreeBSD runs on a wide range of processors, including Intel x86 processors.

The developers of FreeBSD maintain two branches of simultaneous development, the STABLE branch and the CURRENT branch, which offers an aggressive new kernel and features for users. FreeBSD 5.0 was released in early 2003. It introduced support for application threads, advanced multiprocessors, and new platforms, including the IA-64 platform. FreeBSD 5 introduced improved symmetric multiprocessor (SMP) support. FreeBSD 5 also includes new security features that were developed as part of the TrustedBSD project, a project whose purpose is to add trusted operating system functionality to FreeBSD. This functionality includes an extensible access control framework, access control lists, and a new file system. FreeBSD 6.0 was released in late 2005, and 7.0-CURRENT is under development. These versions continue the work on SMP and threading optimization, as well as additional work in the area of advanced 802.11 functionality and added security functionality.

FreeBSD provides an easy way to install software that has been ported to FreeBSD, called the Ports Collection. Using the Ports Collection, software can be installed using the make command, with little extra work. In particular, most applications are automatically downloaded from the Internet, patched and configured if necessary, compiled, installed, and registered in the package database. Over 14,000 pieces of software are currently available in the Ports Collection. FreeBSD also provides binary compatibility with Linux so that FreeBSD users can run applications developed for Linux that are distributed only in binary form.

To learn more about FreeBSD go to http://www.freebsd.org/.

NetBSD

NetBSD was born in 1993; its first multiplatform release, NetBSD 1.0, was introduced in 1994. NetBSD replaced source code based on 4.3BSD NET/2 with source code based on 4.4BSD-lite, making it freely redistributable without restriction. NetBSD is noted for the quality of its design and implementation. It was developed using 4.3BSD NET/2 and 386BSD as the base. The name NetBSD comes from the importance of the Internet in the distributed way it was developed.

NetBSD is noted for its portability, as well as for the ease of this portability. To emphasize this, the motto for NetBSD is “Of course it runs NetBSD.” Currently, NetBSD runs on more than 50 different hardware platforms, ranging from 64-bit machines, to desktop systems, to handheld devices and embedded systems.

In 1998, NetBSD 1.3 introduced a Package Collection (pkgsrc), which provides the changes needed so that a large collection of freely available software can be run on NetBSD. NetBSD 2.0 was released in 2004. With this release NetBSD introduced support for symmetric multiprocessing (SMP) for several CPU architectures, as well as a native threads implementation. With release 2.0, approximately 50 different platforms were supported.

The current release, NetBSD 3.0, was released at the end of 2005. NetBSD 3.0 supports the Xen Virtual Machine Monitor, which allows NetBSD to support execution of multiple guest operating systems at high level of performance and with resource isolation. Because of the portability of NetBSD, it was long said that NetBSD is portable to every type of machine except perhaps a kitchen toaster. However, with this new release, NetBSD now can control a kitchen toaster through the porting of the operating system to an embedded-system single-board computer that can be housed in the empty space of a toaster. Over 5,700 third-party packages are now supported in pkgrc.

NetBSD also provides system-call level binary compatibility with Linux, FreeBSD, Darwin, Solaris, HP-UX, Solaris, and UnixWare. This allows NetBSD users to run many applications that are distributed only in binary form for other UNIX variants.

For more information about NetBSD, go to http://www.NetBSD.org/.

OpenBSD

OpenBSD was split off from NetBSD by its founder Theo de Raadt in 1994. The initial release of OpenBSD was made in 1996. The project introduces a new release every six months, maintained and supported for one year. It is noted for strong support of security, offering security features and capabilities not found in most other UNIX variants. OpenBSD is based entirely on open-source code that can be licensed free of restrictions. The developers of OpenBSD make extra efforts to audit the source code for bugs and for security problems. As in other BSD-based variants of UNIX, the kernel and user programs of NetBSD are developed together in a single source repository.

The latest release is OpenBSD 3.8, which was released in late 2005. OpenBSD currently runs on 16 different hardware platforms. Third-party software is available as binary packages or may be built from source using its ports collection.

For more information about OpenBSD, go to http://www.openbsd.org/.

Solaris

The original operating system of Sun Microsystems was called the SunOS. It was based on UNIX System V Release 2 and 4.3BSD. In 1991, Sun Microsystems set up SunSoft as a separate subsidiary for the development and marketing of software, including operating systems. At its inception, SunSoft began the task of migrating from the SunOS to a new version of UNIX based on UNIX SVR4. SunSoft’s first version of UNIX, Solaris 1.0, was an enhanced version of the SunOS.

With Solaris 2.0, SunSoft moved to an operating system based on SVR4. Although Solaris 2.0 was the first “official” version of Solaris, it was not widely used due to the limited number of workstations it supported. The first version of Solaris to run on all Sun SPARC-based workstations and Intel x86-based workstations was Solaris 2.1, released in late 1992.

The next significant version was Solaris 2.3, released in November 1993, which introduced many changes to the Solaris environment, included the latest version of the X Window System and began using Display PostScript for some of its graphics subsystems. Solaris 2.3 was also POSIX compliant. Solaris 2.4 was released in 1994; it included support for Motif. Solaris 2.5 was released in 1995 and included many new features such as the Common Desktop Environment (CDE), POSIX Threads, and NFS over TCP.

Solaris 2.6, the first version of Solaris to add support for Java, was released in late 1997. Solaris 2.6 also conformed to the UNIX 95 standard from X/OPEN and contained Y2K fixes.

Solaris 7 (the designation 2.7 was dropped in favor of simply 7) was released in 1998; it included many new features for improved usability and reliability. Some of the improvements are support for 64-bit applications and web-based administration and configuration.

Solaris 8 was introduced in 2000. It includes many performance and administration enhancements, including a network cache accelerator for serving web pages, support for clustering of processors, automatic dynamic reconfiguration for reallocating system resources, hot-patching capabilities, live updating for the operating system, and centralized management capabilities. It also provides security enhancements, including a built-in firewall, support for Kerberos, role-based access control, and support for IPsec (IP security) which enables secure, authenticated connections over the Internet. It introduced support for IP version 6, integrated into its NFS/RPC (Network File System/Remote Procedure Call) and NIS/NIS+ (Network Information Services). Solaris 8 also includes the StarOffice 5.1 Productivity Suite, which provides a word processor, a spreadsheet program, a presentation program, a database program, and so on. With this release, Sun began offering its Solaris software free of charge.

Solaris 9 was released in 2002; it includes enhancements to system administration that gave administrators the ability to allocate resources on a system, to monitor usage of resources, and to generate accounting information about system usage. It introduced a new graphical user interface, called Web Start, for system administrations. Solaris 9 also supports the Secure Shell, used for secure connections. Solaris 9 also supports a new fixed-priority scheduling class for processes and a directory server for enterprise-wide users and resources.

In 2005 Sun released its most recent version of Solaris, Solaris 10. Solaris 10 on Sparc-based systems has been registered as a certified UNIX 03 product by the Open Group. Furthermore, to counter the popularity of Linux, Sun has engineered Solaris 10 for use on Intel x86 and AMD 64-based systems. Sun has introduced performance enhancements for these lower-end platforms. For server and for enterprise use, Solaris 10 provides enhancements to resource management. Limits can now be placed on resource use by applications so that systems are not overwhelmed by out-of-control applications. It allows systems to be logically partitioned into zones, each with its own specific functionality using NI containers. Solaris 10 also supports authentication using smart cards. Binary compatibility between Solaris 10 and Linux has been introduced. In 2005, Sun also released OpenSolaris, an open-source version of Solaris, so that outside contributions could help Solaris evolve.

Consult the Sun Microsystems web site, http://www.sun.com/solaris/, for more information about Solaris. For information on obtaining Solaris free of charge, go to http://www.sun.com/software/solaris/get.jsp. Additional information about OpenSolaris can be found at http://www.opensolaris.org.

MAC OS X

The Mac OS, the operating system developed by Apple Computer for its Macintosh computers, was first developed in 1984. The original versions of this operating system were very different from other operating systems, including UNIX. In particular, the Mac OS had an entirely graphical user interface with no command-line interface. However, the original Mac OS hindered the development of more modern versions of the Mac OS. The original architecture of the Mac OS was used up until Mac OS 9. Apple Computer decided to build new versions of the Mac OS, beginning with Mac OS X, on a UNIX-like operating system. To accomplish this, they developed Darwin, first released in 2000, which is a free, open-source variant of UNIX and the core upon which Mac OS X is built. The kernel of Darwin, called XNU, is based on the kernels of FreeBSD 5 and Mach 3, developed at Carnegie Mellon University. As an aside, Apple Computer’s first variant of UNIX was A/UX (from Apple’s UNIX). A/UX 3 merged the functionality of the UNIX System with the Macintosh System 7 operating system. A/UX 3 was based on UNIX System V Release 2.2 but included many extensions from System V Releases 3 and 4 and from 4.2BSD and 4.3BSD.

The initial release of Mac OS X, Version 10.0, called Cheetah, was introduced in early 2001. (Versions of Mac OS X are named after big cats.) This release was incomplete and slow, and few applications ran on it. However, it was a release upon which future versions could be built. Version 10.1, called Puma, was released in late 2001, which improved system performance and provided missing features. Mac OS X version 10.2, called Jaguar, was introduced in 2002. Jaguar was considered to be the first solid release of Mac OS X; it provides performance enhancements, an improved user interface, and over 150 separate enhancements. The next release, Mac OS X version 10.3, called Panther, was introduced in 2003. Panther provided further performance enhancements, an extensive update to the user interface, and greater interoperability with Microsoft Windows. Mac OS version 10.4, called Tiger, was introduced in 2005. Among the new features introduced in Jaguar are Spotlight, a fast content and metadata-based file search tool, and support for 64-bit platforms and Intel x86 platforms. Mac OS Version 10.5, named Leopard, will be released in early 2007.

Although Mac OS X is not open source, Darwin, the operating system upon which it is built, is open source. Furthermore, in 2002, Apple and the Internet Systems Corporation founded OpenDarwin, a community set up to enable the cooperative development of new versions of Darwin. OpenDarwin develops new releases of the Darwin operating system. This group also offers DarwinPorts, which provides an easy way to install various open-source software on versions of Darwin and Mac OS X systems. For more about OpenDarwin, go to http://www.opendarwin.org/, and for more on DarwinPorts, go to http://darwinports.opendarwin.org/.

AIX

IBM’s version of UNIX is called AIX (short for Advanced Interactive eXchangeI) and is primarily developed for use on IBM workstations. IBM has invested billions of dollars in the development of its UNIX servers, both for hardware development and development of AIX. The fruits of this investment can be seen in the increasing power and added capabilities of AIX that make AIX an extremely competitive version of UNIX for servers.

AIX Version 1 was released in 1986 and was based on UNIX System V Release 3. In subsequent releases, source code from BSD 4.2 and BSD 4.3 was introduced into AIX. Version 2 was released in 1987. AIX Version 3 was released in 1990 as a developer release licensed only to OSF. Release 1 of AIX Version 3 introduced the Journaled File System (JFS).

Version 4 of AIX, denoted by AIX 4, was introduced in 1994. In 1995, the CDE desktop environment replaced the Motif X Window Manager in AIX 4. Support for 64-bit architectures was introduced in AIX 4.3 in 1997. AIX 4.3 was registered with the UNIX 98 mark by the Open Group and conforms with the POSIX 1 and POSIX 2 standards.

The latest version of AIX is AIX 5L, released in 2001. The letter L in AIX 5L indicates a strong affinity of this operating system to Linux; AIX 5L incorporates libraries of Linux routines and application programming interfaces that enable almost all Linux applications to run on AIX 5L. The current release, AIX 5L Version 5.3, supports as many as 64 central processing units and a total of two terabytes of RAM. The JFS2 file system has been introduced to AIX 5L. It supports files and partitions as large as 16 terabytes. Many other enhancements have been made to AIX in AIX 4 and AIX 5L, especially in the areas of scalability, security, performance, server capabilities, networking, and administration. Some versions of AIX 5L are UNIX 03-registered products. For more information about AIX, including features, consult the following page on the IBM web site: http://www.austin.ibm.com/software/aix_os.html.

HP-UX

The variant of the UNIX operating system developed and sold by Hewlett-Packard for use on its computers and workstations is called HP-UX. The first version of HP-UX was introduced in 1986. HP-UX was originally based on UNIX System V Release 2.0, but many enhancements have been introduced through the years. Significant advances were made with the introduction of HP-UX 9.0 in 1992, which provided support for workstations. HP-UX 9.0 met many standards, including POSIX 1003.1 and 1003.2, XPG4, and the SVID 2 and 3. It incorporated many features of 4.3BSD and a graphical user interface, called the Visual User Environment (VUE). In 1995 HP-UX 10.0 was introduced, providing enhancements in networking, system management, security, and many other areas. It incorporated the SVR4 File System Directory Layout structure. HP-UX 10.0 added conformance to the Single UNIX Specification and POSIX 1003.1b (Real Time Standard). Furthermore, HP-UX 10.0 included support for the Common Desktop Environment (CDE). It also met the C2 level of security (controlled access protection) specified by the National Computer Security Center.

HP-UX 11.0, released in 1997, provides a 64-bit operating environment and includes many features needed for servers running mission-critical applications, as well as many new features for workstations, including increasing networking and 3-D graphics support. Of the many subsequent substantial releases, HP-UX 11.11, released in 2000, is the most noteworthy. This release, also known as HP 11 i, introduced the notion of operating environments, which are bundled groups of layered applications designed for specific types of use. Available types include Foundation (designed for use by web servers and content servers), Enterprise (designed for use by database servers), Mission Critical (designed for use for back-end application servers and transaction processing), Minimal Technical (designed for use on general-purpose workstations), and Technical Computing (designed for use on compute-intensive workstations).

You can obtain more information about HP-UX at the HP web site; start with the page at http://www.hp.com/unixwork/.

UNIXWARE

The Santa Cruz Operation originally based its operating systems on UNIX System V/386 Release 3.2, a version of UNIX System V Release 3 designed for use on Intel 80386 processors. SCO has evolved this original version of UNIX into a family of operating system in its OpenServer product line. The Santa Cruz Operation also offered UnixWare, a UNIX variant jointly developed by the AT&T UNIX Systems Laboratory and Novell, following the sale of all UnixWare products by Novell to SCO. UnixWare 2, based on an integration of UNIX System V Release 4.2 and Novell NetWare, which supports client/server computing, was released in 1995.

The Santa Cruz Operation, as the owner of UNIX System V, developed System V Release 5, concentrating on further developing the technology of the UNIX kernel. The SVR5 kernel was optimized for large-scale server applications. Among the areas of improvement in SVR5 were system performance, system capacity and scalability, and reliability and availability. Performance gains resulted from improved process synchronization, scheduling, and memory management. System capacity and enhanced scalability result from support of up to 64 GB of main memory, up to 1TB file and file systems, and 512 logical disks. The higher availability and reliability result from support for server clustering and built-in device fail-over capabilities. SVR5 also provides support for 64-bit file systems and implements 64-bit commands, libraries, and APIs.

The Santa Cruz Operation based its subsequent UnixWare products on the System V Release 5 kernel. Their latest release of UnixWare was UnixWare 7. Because it is based on the SVR5 kernel, UnixWare 7 supports 64-bit files systems and operations and includes development tools that support 64-bit integer operations. UnixWare 7 includes the Common Desktop Environment (CDE). It also includes an integrated Netscape browser and web server. It provides Java-based administration and support with a web interface and access and management of applications over a network. UnixWare 7 also includes support for Java. The Santa Cruz Operation also evolved the original version of UNIX into a family of operating systems in its OpenServer product line.

In 2000 the Santa Cruz Operation sold the rights to UnixWare to Caldera Systems. Caldera later changed its name to the SCO Group. (The Santa Cruz Operation was originally known as SCO; they changed their name to Tarantella when they sold UnixWare and the part of their company dealing with operating systems to Caldera.) The SCO Group has continued to develop further releases of UnixWare; the latest release is UnixWare 7.1.4. New features in this release include added security functionality, including support for IPsec and support for OpenSSH and OpenSSL, and advanced hyperthreading capabilities. Also, the SCO Group has continued to evolve the OpenServer product line; in 2005, the SCO Group released SCO OpenServer 6, which is bundled with many open-source applications, including Apache, Samba, MySQL, OpenSSH, Firefox, and KDE. OpenServer 6 provides many improvements over OpenServer 5, including vastly improved SMP support, with support for as many as 32 x86-family processors on a single server and support for files larger than one terabyte on a partition.

Go to http://www.sco.com/products/unix/ for more information about OpenServer and UnixWare operating systems.

Tru64 UNIX

For many years the Digital Equipment Corporation (DEC) sold computers running their version of UNIX, which was called ULTRIX and was based on 4.2BSD. Later, with the advent of their Alpha processor-based computers, they focused on a different UNIX variant, DEC OSF/1, based on the OSF/1 operating system developed by the Open Systems Foundation. DEC OSF/1 included extensive enhancements beyond what is included in OSF/1. In particular, it provided 64-bit support, real-time support, enhanced memory management, symmetric multiprocessing, and a fast-recovery file system. DEC OSF/1 integrated OSF/1, System V, and BSD components, ran under a Mach kernel, and provided backward compatibility for ULTRIX applications. DEC OSF/1 was compliant with Spec 1170 (except for curses support) and with POSIX 1003.1, POSIX 1003.2, and X/Open XPG4. DEC OSF/1 was renamed Digital UNIX.

In January 1998, Compaq Computer Corporation purchased DEC and continued the development of Digital UNIX. They have renamed Digital UNIX, giving it the new name Tru64 UNIX, highlighting that it is a 64-bit operating system that can take advantage of 64-bit hardware. This UNIX variant includes a wide range of features designed to support highly reliable networked applications running on servers. In 2002, HP purchased Compaq. HP announced its intention to migrate many of Tru64 UNIX’s more unique features to HP-UX. The current release is Tru64 UNIX 5.1; HP has committed to support this operating system until at least 2011.

For more information about Tru64 UNIX, consult the HP Tru64 web pages at http://h30097.www3.hp.com/.

IRIX

IRIX is a proprietary version of UNIX System V Release 4 provided by Silicon Graphics for use on its MIPS-based workstations. IRIX is a 64-bit operating system, which is one of its features that optimize its performance for graphics applications requiring intensive CPU processing. The current release of IRIX, IRIX 6.5, offers scalability, large-scale data management, real-time 3-D visualization capability, and middleware platforms. IRIX has been designed so that it provides functionality in many areas, including server support, applications launching, and digital media support. IRIX is compliant with many UNIX standards. Consult the Silicon Graphics web site, http://www.sgi.com/, for more information about IRIX.




UNIX. The Complete Reference
UNIX: The Complete Reference, Second Edition (Complete Reference Series)
ISBN: 0072263369
EAN: 2147483647
Year: 2006
Pages: 316

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