Chapter 4 : Glossary

• account: on a Unix system, a login name, a personal directory, a password and a shell which allow a person to connect to this system.
• alias: mechanism used in a shell in order to make it substitute a string by another before executing the command. You can see all aliases defined in the curent session by typing alias at the prompt.
• APM: Advanced Power Management. A feature used by some BIOSes in order to make the machine enter a standby state after a given period of inactivity. On laptops, APM is also responsible for reporting the battery status and, if it supports it, the estimated remaining lifetime.
• atomic: a set of operations is said to be atomic when it executes all in once, and cannot be interrupted.
• background: in shell context, a process is running in the background if you can type commands while this process is running. See also job, foreground.
• bit: stands for BInary uniT. A single digit which can take the values 0 or 1, because calculation is yielded in base two.
• block mode files: files whose contents are buffered. All read/write operations for such files go through buffers, which allows for asynchronous writes on the underlying hardware, and for reads, not to read again what is already in a buffer. See also buffer, buffer cache.
• boot: the procedure taking place when a computer is switched on, where peripherals are recognized one after the other, and where the operating system is loaded into memory.
• bootdisk: a bootable floppy disk containing the code necessary to load the operating system from the hard disk (sometimes it is self-sufficient).
• BSD: Berkeley Software Distribution. A Unix variant developed at the Berkeley University computing department. This version has always been considered more advanced technically than the others, and has brought many innovations to the computing world in general and to Unix in particular.
• buffer: a small portion of memory with a fixed size, which can be associated to a block mode file, a system table, a process and so on. The coherency of all buffers is maintained by the buffer cache. See buffer cache.
• buffer cache: a crucial part of an operating system kernel, it is in charge of keeping all buffers up to date, shrinking the cache when needed, clearing unneeded buffers and more. See buffers.
• bug: illogical or incoherent behaviour of a program in a special case, or a behaviour which does not follow the documentation issued for the program. Often, new features introduce new bugs in a program.
• byte: eight consecutive bits, interpreted in base two as a number between 0 and 255. See bits.
• case: when taken in the context of strings, the case is the difference between lowercase letters and uppercase (or capital) letters.
• CHAP: Challenge-Handshake Authentication Protocol: protocol used by ISPs to authenticate their clients. In this scheme, a value is sent to the client (the machine who connects), the client calculates a hash from this value which it sends to the server, and the server compares the hash with the one it has calculated. See also PAP.
• character mode files: files whose content is not buffered. All input/output is physically performed immediately. They correspond to data flows.
• CIFS: Common Internet FileSystem The predecessor of the SMB filesystem, used on DOS systems.
• client: program or computer that episodically and temporarily connects to another program or computer to give it orders or ask for information. It is one of the components of a client/server system.
• client/server system: system or protocol consisting of a server and one or several clients.
• command line: what is provided by a shell and allows the user to type commands directly. Also subject of an eternal "flame war" between its adepts and its detractors :)
• command mode: under VI or one of its clones, it is the state of the program in which pressing a key (this above all regards letters) will not insert it in the file being edited, but instead perform an action specific to the said key (unless the clone has remappable commands and you have customized your configuration). You may get out of it typing one of the "back to insertion mode" commands: 'i', 'I', 'a', 'A', 's', 'S', 'o', 'O', 'c', 'C', ...
• completion: ability of a shell to automatically expand a substring to a filename, user name or other, if the substring is not ambiguous.
• cookies: temporary files written on the local hard disk by a remote web server. It allows for the server to be aware of a user's preferences when this user connects again.
• DHCP: Dynamic Host Configuration Protocol. A protocol designed for machines on a local network to dynamically get an IP address.
• DMA: Direct Memory Access. A facility used on the PC architecture which allows for a peripheral to read or write from main memory without the help of the CPU. PCI peripherals use bus mastering and do not need DMA.
• DPMS: Display Power Management System. Protocol used by all modern monitors in order to manage power saving features. Monitors supporting these features are commonly called "green monitors".
• ELF: Executable and Linking Format. This is the binary format used by most Linux distributions nowadays.
• environment variables: a part of a process' environment. Environment variables are directly viewable from the shell. See also process.
• FAT: File Allocation Table. Filesystem used by DOS and Windows.
• FAQ: Frequently Asked Questions: document containing a series of questions/answers about a specific domain. Historically, FAQs appeared in newsgroups, but this sort of document now appears on various web sites, and even commercial products have their FAQ. Generally, they are very good sources of information.
• FDDI: Fiber Distributed Digital Interface. A high-speed network physical layer, which uses optical fiber for communication. Only used on big networks, mainly because of its price.
• FHS: Filesystem Hierarchy Standard. A document containing guidelines for a coherent file tree organisation on Unix systems. Linux-Mandrake complies with this standard.
• FIFO: First In, First Out. A data structure or hardware buffer from which items are taken out in the order they were put in. Unix pipes are the most common examples of FIFOs.
• filesystem: scheme used in order to be able to store files on a physical media (hard drive, floppy) in a consistent manner. Examples of filesystems are FAT, Linux' ext2fs, iso9660 (used by CDROMs) and so on.
• firewall: machine which, in the topology of a local network, is the unique connecting point to the outside network, and which filters, or controls the activity on some ports, or makes sure only some specific IP interfaces may have access to them.
• focus: the fact for a window to receive keyboard events (such as keypresses and keyreleases and mouse clicks, unless they are trapped by the window manager.
• foreground: in shell context, the process in the foreground is the one which is currently running. You have to wait for such a process to finish in order to be able to type commands again. See also job, background.
• framebuffer: memory projection of a video card's RAM into main memory. This allows for applications to access the video RAM without the chore of having to talk to the card. All high-end graphical workstations use framebuffers, for example.
• FTP: File Transfer Protocol. This is the standard Internet protocol used to transfer files from one machine to another.
• gateway: link connecting two IP networks.
• GIF: Graphics Interchange Format. An image file format, widely used on the web. GIF images are compressed, and they can even be animated.
• globbing: in the shell, the ability to group a certain set of filenames with a globbing pattern. See globbing pattern.
• globbing pattern: a string made of normal characters and special characters. Special characters are interpreted and expanded by the shell.
• GNU: GNU's Not Unix. The GNU project has been initiated by Richard Stallman at the beginning of the 80s, which aims at delevopping a free operating system ("free" as in "free speech"). Currently, all tools are there, except... the kernel. The GNU project kernel, Hurd, is not rock solid yet. Linux borrows two things from GNU: its C compiler, GCC, and its license, the GPL. See GPL.
• GPL: General Public License. The license of the Linux kernel, it goes the opposite way of all proprietary licenses in that it gives no restriction as to copying, modifying and redistributing the software, as long as the source code is available. The only restriction, if one can call it so, is that the persons to which you redistribute it must also benefit from the same rights.
• GUI: Graphical User Interface. A program using menus, buttons, colors, and different fonts to look easier to use at a first glance. It needs an X server.
• home directory: often abbreviated by "home", this is the name for the personal directory of a given user. See also account.
• HTML: HyperText Markup Language. The language used to create web documents.
• HTTP: HyperText Transfer Protocol. The protocol used to connect to websites and retrieve HTML documents.
• IDE: Integrated Drive Electronics. The most widely used bus on today's PCs for hard disks. An IDE bus can contain up to two devices, and the speed of the bus is limited by the device on the bus which has the slower command queue (and not the slower transfer speed!).
• inode: entry point leading to the contents of a file on a Unix-like filesystem. An inode is identified in a unique way by a number, and contains meta-information about the file it refers to, such as its access times, its type, its size, but not its name!
• insert mode: under VI or one of its clones, it is the state of the program in which pressing a key will insert it in the file being edited (except pathological cases like the completion of an abbreviation, right justify at the end of the line, ...). One gets out of it pressing the key Esc (or Ctrl-[).
• IRC: Internet Relay Chat. One of the few Internet standards for live speech. It allows for channel creation, private talks, and also file exchange. It is also designed in order to be able to make servers connect to each other, which is why several IRC networks exist today: Undernet, DALnet, EFnet to name a few.
• ISA: Industry Standard Architecture. The very first bus used on PCs, it is slowly being abandoned in favor of the PCI bus. Some hardware manufacturers still use it, though. It is still very common that SCSI cards supplied with scanners, CD writers, ... are ISA. Too bad.
• ISDN: Integrated Services Digital Network. A set of communication standards for allowing a single wire or optical fibre to carry voice, digital network services and video. It has been designed in order to eventually replace the current phone systems.
• ISO: International Standards Organisation. A group of companies, consultants, universities and other sources which elaborates standards in various domains, including computing. The papers describing standards are numbered. The standard number 9660, for example, describes the filesystem used on CDROMs.
• ISP: Internet Service Provider. A company which sells Internet access to its customers, whether the access be over phonelines or dedicated lines.
• job: in shell context, a job is a process running in the background. You can have several jobs in a same shell and control these jobs. See also background, foreground.
• JPEG: Join Photographic Experts Group. Another very common image file format. JPEG is mostly suited for compressing real-world scenes, and does not work very well on non-realistic images.
• kill ring: under Emacs, it is the set of text areas cut or copied since the beginning of the editor, which may be recalled to be inserted again, and which is organized as a ring.
• LAN: Local Area Network. Generic name given to a network of machines connected to the same physical wire.
• LDP: Linux Documentation Project. A nonprofit organisation which maintains Linux documentation. Its mostly known documents are HOWTOs, but it also maintains FAQs, and even a few books.
• link: reference to an inode in a directory, therefore giving a (file) name to the inode.
• login: connection name for a user on a Unix system, and the fact to connect.
• loopback: virtual network interface of a machine with itself, which allows the running programs not to have to take into account the special case where two network entities are in fact the same machine.
• major: number specific to the device class.
• manual page: a small document containing the definition of a command and its usage, to be consulted with the man command. The first thing one should (learn how to) read when hearing of a command he doesn't know :)
• MBR: Master Boot Record. Name given to the first sector of a bootable hard drive. The MBR contains the code used to load the operating system into memory or a bootloader (such as LILO), and the partition table of this hard drive.
• MIME: Multipurpose Internet Mail Extensions. A string of the form type/subtype describing the contents of a file attached in an e-mail. This allows MIME-aware mail clients to define actions depending on the type of the file.
• minor: number precising the very device we are talking about.
• MPEG: Moving Pictures Experts Group. An ISO committee which generates standards for video and audio compression. MPEG is also the name of their algorithms. Unfortunately, the license for this format is very restrictive, and as a consequence there is still no Open Source MPEG players...
• named pipe: a Unix pipe which is linked, as opposed to pipes used in shells. See also pipe, link.
• naming: a word commonly used in computing for a method to identify objects. You will often hear of "naming conventions" for files, functions in a program and so on.
• NCP: NetWare Core Protocol: protocol defined by Novell Novell to access Novell NetWare file and print services.
• NFS: Network FileSystem. A network filesystem created by Sun Microsystems in order to share files across a network in a transparent way.
• NIC: Network Interface Controller: adapter installed in a computer which provides a physical connection to a network, such as an Ethernet card.
• NIS: Network Information System. NIS was also known as "Yellow Pages", but British Telecom holds a copyright on this name. NIS is a protocol designed by Sun Microsystems in order to share common information across a NIS domain, which can gather a whole LAN, part of this LAN or several LANs. It can export password databases, service databases, groups information and more.
• null, character: the character or byte number 0, it is used to mark the end of a string. Its technical name is NULL.
• pager: program displaying a text file one screenful at a time, and making it easy to move back and forth and search for strings in this file. We advise you to use less.
• PAP: Password Authentication Protocol: protocol used by ISPs to authenticate theirs clients. In this scheme, the client (you) sends an identifier/password pair to the server, which is not encrypted. See also CHAP.
• patch, to patch: file holding a list of corrections to issue to a source code in order to add new features, to remove bugs, or to modify it according to one's wishes and needs. The action consisting of the application of these corrections to the archive of source code.
• PCI: Peripheral Components Interconnect. A bus created by Intel and which is today the standard bus for PC architectures, but other architectures use it too. It is the successor of ISA, and it offers numerous services: device identification, configuration information, IRQ sharing, bus mastering and more.
• PCMCIA: Personal Computer Memory Card International Association: more and more commonly called "PC Card" for simplicity reasons, this is the standard for external cards attached to a laptop: modems, hard disks, memory cards, Ethernet cards and more. The acronym is sometimes humorously expanded to People Cannot Memorize Computer Industry Acronyms...
• pipe: a special Unix file type. One program writes data into the pipe, and another program reads the data at the other end. Unix pipes are FIFO, so the data is read at the other end in the order it was sent. Very widely used with the shell. See also named pipe.
• plugin: add-on program used to display or play some multimedia content found on a web document. It can usually be easily downloaded if your browser is not yet able to display or play that kind of information.
• PNP: Plug'N'Play. First an add-on for ISA in order to add configuration information for devices, it has become a more widespread term which groups all devices able to report their configuration parameters. As such, all PCI devices are Plug'n'Play.
• PNG: Portable Network Graphics. Image file format created mainly for web use, it has been designed as a patent-free remplacement for GIF and also has some additional features.
• process: in a Unix context, a process is an instance of a program being executed, together with its environment.
• prompt: in a shell, this is the string before the cursor. When you see it, you can type your commands.
• proxy: a machine which sits between a network and the Internet, whose role is to speed up data transfers for the most widely used protocols (HTTP and FTP, for example). It maintains a cache of previous demands, which avoids the cost of asking for the file again if another machine asks for the same thing. Proxies are very useful on low bandwidth networks (understand: modem connections). Sometimes too, the proxy is the only machine able to access the outside.
• RAID: Redundant Array of Independent Disks. A project initiated at the computing science department of Berkeley University, in which the storage of data is spread along an array of disks.
• RAM: Random Access Memory. Term used to identify a computer's main memory.
• regular expression: a powerful theoretical tool which is used to search and match text strings. It lets one specify patterns these strings must obey. Many Unix utilities use it: sed, awk, grep, perl among others.
• RFC: Request For Comments. RFCs are the official Internet standard documents. They describe all protocols, their usage, their requirements and so on. When you want to learn how a protocol works, pick up the corresponding RFC.
• RPM: Redhat Package Manager. A packaging format developed by Red Hat in order to create software packages, and used in many Linux distributions, including Linux-Mandrake.
• SCSI: Small Computers System Interface. A bus with a high throughput designed to allow for several types of peripherals. Unlike IDE, a SCSI bus is not limited by the speed at which the peripherals accept commands. Only high-end machines integrate a SCSI bus directly on the motherboard, PCs need add-on cards.
• server: program or computer that proposes a feature or service and awaits the connections from clients to execute their orders or give them the information they ask. It is one of the components of a client/server system.
• shadow passwords: a password management suite on Unix systems in which the file containing the encrypted passwords is no more world-readable, whereas it is when using the normal password system.
• SMB: Server Message Block. Protocol used by Windows machines (9x or NT) for file and printer sharing across a network. See also CIFS.
• socket: file type corresponding to any network connection.
• soft links: see "symbolic links".
• standard error: the file descriptor number 2, opened by every process, used by convention to print error messages, and the terminal screen by default. See also standard input, standard output.
• standard input: the file descriptor number 0, opened by every process, used by convention as the file descriptor from which the process receives data. See also standard error, standard output.
• standard output: the file descriptor number 1, opened by every process, used by convention as the file descriptor in which the process prints its output. See also standard error, standard input.
• SVGA: Super Video Graphics Array: video display standard defined by VESA for the PC architecture. The resolution is 800 x 600 x 16 colours.
• symbolic links: special files, containing nothing but a string, and any access to them is equivalent to an access to the file whose name is said string, which can exist or not, and the path of which can be given in a relative of an absolute way.
• theme-able: a graphical application is theme-able if it is able to change its appearance in real time. Many window managers are theme-able as well.
• traverse: for a directory on a Unix system, this means that the user is allowed to go through this directory, and possibly to directories under it. This requires that the user has the execute permission on this directory.
• URL: Uniform Resource Locator. A string with a special format used to identify a resource on the Internet in a unique way. The resource can be a file, a server and others. The syntax for a URL is

  protocol://server.name[:port]/path/to/resource.

  When only a machine name is given and the protocol is http://, it defaults to retrieving the file index.html on the server.

• VESA: Video Electronics Standards Association. An industry standards association aimed at the PC architecture. It is the author of the SVGA standard, for example.
• virtual consoles: the ability to run several terminals over a same physical terminal. On PCs, the physical terminal is the keyboard and screen.
• window manager: the program responsible for the "look and feel" of a graphical environment and dealing with window bars, frames, buttons, root menus, and some keyboard shortcuts. Without it it would be hard or impossible to have virtual desktops, to resize windows on the fly, to move them around, ...