Реферат: Linux 2 Essay Research Paper Table of

The X Window System, or simply X, is a standard graphical user interface (GUI) for UNIX machines and is a powerful environment, which supports many applications. Using the X Window System, you can have multiple terminal windows on the screen at once, each having a different login session. A pointing device like a mouse is often used with X, although it is not required. Many X-specific applications have been written, including games, graphics and programming utilities, and documentation tools. LINUX and X make your system a bona fide workstation. With TCP/IP networking, your LINUX machine can display X applications running on other machines. The X Window System was originally developed at the Massachusetts Institute of Technology and is freely distributable. Many commercial vendors have distributed proprietary enhancements to the original X Window System as well. The version of X for LINUX is XFree86, a port of X11R6, which is freely distributable. XFree86 supports a wide range of video hardware, including VGA, Super VGA, and accelerated video adapters. XFree86 is a complete distribution of the X Windows System software, and contains the X server itself, many applications and utilities, programming libraries, and documents. Standard X applications include xterm, a terminal emulator used for most text-based applications within a window, xdm, which handles logins, xclock, a simple clock display, xman, a X-based manual page reader, and xmore. There are manu other application written which includes spreadsheets, word processors, graphics programs, and web browsers like the Netscape Navigator. Theoretically, any application written for X should compile cleanly under LINUX. The interface of the X Window System is controlled largely by the window manager. This user-friendly program is in charge of the placement of windows, the user interface for resizing and moving them, changing windows to icons, and the appearance of window frames, among other tasks. XFree86 includes twm, the classic MIT window manager, and advanced window managers like the Open Look Virtual Window Manager (olvwm) are available. Popular among LINUX users is fvwm–a small window manager that requires less than half the memory of twm. It provides a 3-dimensional appearance for windows and a virtual desktop. The user moves the mouse to the edge of the screen, and the desktop shifts as though the display was much larger than it really is. fvwm is greatly customizable and allows access to functions from the keyboard as well as mouse. Many LINUX distributions use fvwm as the standard window manager. A version of fvwm called fvwm95-2 offers Microsoft Windows 95-like look and feel. The XFree86 distribution includes programming libraries for programmers who wish to develop X applications. Widget sets like Athena, Open Look, and Xaw3D are supported. All of the standard fonts, bitmaps, manual pages, and documentation are included. PEX (a programming interface for 3-dimensional graphics) is also supported. Many X application programmers use the proprietary Motif widget set for development. Several vendors sell single and multiple user licenses for binary versions of Motif. Because Motif itself is relatively expensive, not many LINUX users own it. However, binaries statically linked with Motif routines can be freely distributed.

Networking

LINUX supports two primary UNIX networking protocols: TCP/IP and UUCP. TCP/IP (Transmission Control Protocol/Internet Protocol) is the networking paradigm which allows systems all over the world to communicate on a single network, the Internet. With LINUX, TCP/IP, and a connection to the Internet, you can communicate with users and machines via electronic mail, Usenet news, and FTP file transfer. Most TCP/IP networks use Ethernet as the physical network transport. LINUX supports many popular Ethernet cards and interfaces for personal computers, including pocket and PCMCIA Ethernet adapters. However, because not everyone has an Ethernet connection at home, LINUX also supports SLIP (Serial Line Internet Protocol) and PPP (Point-to-Point Protocol), which provide Internet access via modem. Many businesses and universities provide SLIP and PPP servers. In fact, if your LINUX system has an Ethernet connection to the Internet and a modem, your system can become a SLIP or PPP server for other hosts. NFS (Network File System) lets your system seamlessly share file systems with other machines on the network. FTP (File Transfer Protocol) lets you transfer files with other machines. sendmail sends and receives electronic mail via the SMTP protocol; C-News and INN are NNTP based new systems; and telnet, rlogin, and rsh let you log in and execute commands on other machines on the network. finger lets you get information about other Internet users. LINUX also supports Microsoft Windows connectivity via Samba and Macintosh connectivity with AppleTalk and LocalTalk. Support for Novell’s IPX protocol is also included. The full range of mail and newsreaders is available for LINUX, including elm, pine, rn, nn, and tin. Whatever your preference, you can configure a LINUX system to send and receive electronic mail and news from all over the world. The system provides a standard UNIX socket-programming interface. Virtually any program that uses TCP/IP can be ported to LINUX. The LINUX X server also supports TCP/IP, and applications running on other systems may use the display of your local system. UUCP (UNIX-to-UNIX Copy) is an older mechanism to transfer files, electronic mail, and electronic news between UNIX machines. Historically, UUCP machines are connected over telephone lines via modem, but UUCP is able to transfer data over a TCP/IP network as well. If you do not have access to a TCP/IP network or a SLIP or PPP server, you can configure your system to send and receive files and electronic mail using UUCP.

System Administration

LINUX differentiates between different users. What they can do to each other and the system is regulated. File permissions are arranged so that normal users cannot delete or modify files in directories like /bin and /usr/bin. Most users protect their own files with the appropriate permissions so that other users cannot access or modify them. Each user is given an account that includes a user name and home directory. In addition, there are special, system defined accounts which have special privileges. The most important of these is the root account, which is used by the system administrator. By convention, the system administrator is the user, root. There are no restrictions on root. He or she can read, modify, or delete any file on the system, change permissions and owner-ships on any file, and run special programs like those which partition a hard drive or create file systems. The basic idea is that a person who cares for the system logs in as root to perform tasks that cannot be executed as a normal user. Because root can do anything, it is easy to make mistakes that have catastrophic consequences. If a normal user tries inadvertently to delete all of the files in /etc, the system will not permit him or her to do so. However, if root tries to do the same thing, the system does not complain at all. It is very easy to trash a LINUX system when using root. Picture the root account as a special, magic hat that gives you lots of power, with which you can, by waving your hands, destroy entire cities. It is a good idea to be a bit careful about what you do with your hands. Because it is easy to wave your hands in a destructive manner, it is not a good idea to wear the magic hat when it is not needed, despite the wonderful feeling. The best way to prevent accidents is to sit on your hands before you press Enter for any command that is non-reversible.

Conclusion

After LINUX 1.0 was released, work was done on several enhancements. LINUX 1.2 included disk access speedups, TTY improvements, virtual memory enhancements, multiple platform support, quotas, and more. LINUX 2.0 has even more enhancements, including many performance improvements, several new networking protocols, one of the fastest TCP/IP implementations in the world, and far, far more. Even higher performance, more networking protocols, and more device drivers are available in LINUX 2.2. In the final analysis, the greatest irony behind the LINUX phenomenon may be its reliance on the same principal upon which Microsoft has relied: the bottom line. While Microsoft’s bottom line has led to incomplete and disfunctional software, cutting corners, buyouts and legal wrangling, the LINUX bottom line, in financial terms, remains ultimately advantageous. In LINUX, the bottom line is zero. Zero dollars, zero lawsuits, zero buyouts, and zero political concerns. Because LINUX, by its very nature, has avoided nearly every concern with which Microsoft has struggled recently, LINUX appears to have a clear advantage, especially when the technical superiority of the LINUX operating system is considered as well. LINUX may very well be the operating system of choice in the future at its features and performance clearly outguns that of Windows NT. On the other hand, Windows NT do offer a more user-friendly environment than LINUX.

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