About UNIX Part 3

Subject: About UNIX Part 3 Sun Feb 24, 2008 12:04 am

[edit] 2038
Main article: Year 2038 problem
Unix stores system time values as the number of seconds from midnight January 1, 1970 (the "Unix Epoch") in variables of type time_t, historically defined as "signed 32-bit integer". On January 19, 2038, the current time will roll over from a zero followed by 31 ones (01111111111111111111111111111111) to a one followed by 31 zeros (10000000000000000000000000000000), which will reset time to the year 1901 or 1970, depending on implementation. As many applications use OS library routines for date calculations, the impact of this could be felt much earlier than 2038; for instance, 30-year mortgages may be calculated incorrectly beginning in the year 2008.

Since times before 1970 are rarely represented in Unix time, one possible solution that is compatible with existing binary formats would be to redefine time_t as "unsigned 32-bit integer". However, such a kludge merely postpones the problem to February 7, 2106, and could introduce bugs in software that compares differences between two sets of time.

Some Unix versions have already addressed this. For example, in Solaris on 64-bit systems, time_t is 64 bits long, meaning that the OS itself and 64-bit applications will correctly handle dates for some 292 billion years (several times greater than the age of the universe). Existing 32-bit applications using a 32-bit time_t continue to work on 64-bit Solaris systems but are still prone to the 2038 problem.

[edit] Free Unix-like operating systems

Linux is a modern Unix-like systemIn 1983, Richard Stallman announced the GNU project, an ambitious effort to create a free software Unix-like system; "free" in that everyone who received a copy would be free to use, study, modify, and redistribute it. GNU's goal was achieved in 1992. Its own kernel development project, GNU Hurd, had not produced a working kernel, but a compatible kernel called Linux was released as free software in 1992 under the GNU General Public License. The combination of the two is frequently referred to simply as "Linux", although the Free Software Foundation and some Linux distributions, such as Debian GNU/Linux, use the combined term GNU/Linux. Work on GNU Hurd continues, although very slowly.

In addition to their use in the Linux operating system, many GNU packages — such as the GNU Compiler Collection (and the rest of the GNU toolchain), the GNU C library and the GNU core utilities — have gone on to play central roles in other free Unix systems as well.

Linux distributions, comprising Linux and large collections of compatible software have become popular both with hobbyists and in business. Popular distributions include Red Hat Enterprise Linux, SUSE Linux, Mandriva Linux, Fedora Core, Ubuntu, Debian GNU/Linux, Slackware Linux and Gentoo.

A free derivative of BSD Unix, 386BSD, was also released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi), it was clarified that Berkeley had the right to distribute BSD Unix — for free, if it so desired. Since then, BSD Unix has been developed in several different directions, including the OpenBSD and DragonFly BSD variants.

Linux and the BSD kin are now rapidly occupying the market traditionally occupied by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. A measure of this success may be seen when Apple Computer sought out a new foundation for its Macintosh operating system: it chose NEXTSTEP, an operating system developed by NeXT with a freely redistributable core operating system, renamed Darwin after Apple acquired it. It was based on the BSD family and the Mach kernel. The deployment of Darwin BSD Unix in Mac OS X makes it, according to a statement made by an Apple employee at a USENIX conference, the most widely used Unix-based system in the desktop computer market. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern BSDs also typically include some GNU utilities in their distribution, so Apple's combination of parts from NeXT and FreeBSD with Mach and some GNU utilities has precedent.

In 2005, Sun Microsystems released the bulk of the source code to the Solaris operating system, a System V variant, under the name OpenSolaris, making it the first actively developed commercial Unix system to be open sourced (several years earlier, Caldera had released many of the older Unix systems under an educational and later BSD license). As a result, a great deal of formerly proprietary AT&T/USL code is now freely available.

[edit] Branding
See also: list of Unix systems
In October 1993, Novell, the company that owned the rights to the Unix System V source at the time, transferred the trademarks of Unix to the X/Open Company (now The Open Group),[7] and in 1995 sold the related business operations to Santa Cruz Operation.[8] Whether Novell also sold the copyrights to the actual software is currently the subject of litigation in a federal lawsuit, SCO v. Novell. Unix vendor SCO Group Inc. accused Novell of slander of title.

The present owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like"). The term UNIX is not an acronym, but follows the early convention of naming computer systems in capital letters, such as ENIAC and MISTIC.

By decree of The Open Group, the term "UNIX®" refers more to a class of operating systems than to a specific implementation of an operating system; those operating systems which meet The Open Group's Single UNIX Specification should be able to bear the UNIX® 98 or UNIX® 03 trademarks today, after the operating system's vendor pays a fee to The Open Group. Systems licensed to use the UNIX® trademark include AIX, HP-UX, IRIX, Solaris, Tru64, A/UX, Mac OS X 10.5 on Intel platforms[9], and a part of z/OS.

Sometimes a representation like "Un*x", "*NIX", or "*N?X" is used to indicate all operating systems similar to Unix. This comes from the use of the "*" and "?" characters as "wildcard" characters in many utilities. This notation is also used to describe other Unix-like systems, e.g. Linux, Mac OS X, FreeBSD, etc., that have not met the requirements for UNIX® branding from the Open Group.

The Open Group requests that "UNIX®" is always used as an adjective followed by a generic term such as "system" to help avoid the creation of a genericized trademark.

The term "Unix" is also used, and in fact was the original capitalisation, but the name UNIX stuck because, in the words of Dennis Ritchie "when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery, we had just acquired a new typesetter and were intoxicated by being able to produce small caps" (quoted from the Jargon File, version 4.3.3, 20 September 2002). Additionally, it should be noted that many of the operating system's predecessors and contemporaries used all-uppercase lettering, because many computer terminals of the time could not produce lower-case letters, so many people wrote the name in upper case due to force of habit.

Several plural forms of Unix are used to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional "Unixes", but the hacker culture which created Unix has a penchant for playful use of language, and "Unices" (treating Unix as Latin noun of the third declension) is also popular. The Anglo-Saxon plural form "Unixen" is not common, although occasionally seen.

Trademark names can be registered by different entities in different countries and trademark laws in some countries allow the same trademark name to be controlled by two different entities if each entity uses the trademark in easily distinquishable categories. The result is that Unix has been used as a brand name for various products including book shelves, ink pens, bottled glue, diapers, hair driers and food containers. [2].

[edit] Common Unix commands
Wikibooks Guide to Unix has a page on the topic of
CommandsSee also: list of Unix programs
Widely used Unix commands include:

Directory and file creation and navigation: ls cd pwd mkdir rm rmdir cp find touch
File viewing and editing: more less ed vi emacs head tail
Text processing: echo cat grep sort uniq sed awk cut tr split printf
File comparison: comm cmp diff patch
Miscellaneous shell tools: yes test xargs
System administration: chmod chown ps su w who
Communication: mail telnet ftp finger ssh
Authentication: su login passwd

Subject: Re: About UNIX Part 3 Wed Mar 05, 2008 7:35 pm

Hmm.. Ty Done now,, much 2 read Neutral

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