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Linux Guide - P

  • P-code language
    They are like compiled languages in that the source is translated to a compact binary form which is what you actually execute, but that form is not machine code. Instead it's pseudocode (or p-code), which is usually a lot simpler but more powerful than a real machine language. When you run the program, you interpret the p-code. Important p-code languages include Python and Java. See Compiled language and Interpreted language
  • Packet
    The fundamental unit of communication on the Internet.
  • Packet filtering
    The action a device takes to selectively control the flow of data to and from a network. Packet filters allow or block packets, usually while routing them from one network to another (most often from the Internet to an internal network, and vice-versa). To accomplish packet filtering, you set up rules that specify what types of packets (those to or from a particular IP address or port) are to be allowed and what types are to be blocked.
  • Packet Switching
    The method used to move data around on the Internet. In packet switching, all the data coming out of a machine is broken up into chunks, each chunk has the address of where it came from and where it is going. This enables chunks of data from many different sources to co-mingle on the same lines, and be sorted and directed to different routes by routers along the way. This way many people can use the same lines at the same time
  • PAM
    Pluggable Authentication Modules for Linux - a flexible mechanism for authenticating users. Each time a new authentication scheme is developed, it requires all the necessary programs (login, ftpd etc...) to be rewritten to support it. PAM provides a way to develop programs that are independent of authentication scheme. These programs need "authentication modules" to be attached to them at run-time in order to work. Which authentication module is to be attached is dependent upon the local system setup and is at the discretion of the local system administrator.
  • PAP
    Password Authentication Protocol: The usual method of user authentication used on the internet: sending a username and password to a server where they are compared with a table of authorized users.
  • Parallel Processing
    Refers to the concept of speeding-up the execution of a program by dividing the program into multiple fragments that can execute simultaneously, each on its own processor. A program being executed across N processors might execute N times faster than it would using a single processor
  • parameter
    An entity that stores values, somewhat like a variable in a conventional programming language. It can be a name, a number, or one of the special characters.
  • partition
    A contiguous section of blocks on your hard disk that is treated like a completely separate disk by most operating systems
  • Pascal
    An Algol-descended language designed by Niklaus Wirth on the CDC 6600 around 1967-68 as an instructional tool for elementary programming. This language, designed primarily to keep students from shooting themselves in the foot and thus extremely restrictive from a general-purpose-programming point of view, was later promoted as a general-purpose tool and, in fact, became the ancestor of a large family of languages including Modula-2 and Ada
  • password
    A personal identifier used to validate a user's authorization to log into a Linux system
  • password file
    A file, /etc/passwd, that contains basic information about each user authorized to log into a given Linux system. For each user, the file contains a line that gives the user's login name, encrypted password, user identifier, group identifier (if any), home directory, and login program
  • patch
    apply a diff file to an original
  • PD
    Public Domain. Supposedly, the "public" owns the copyright. PD SW is the only SW rightly called "free SW". Note that derivations of PD SW need not remain PD
  • PDC
    Primary Domain Controler. This stores security and user account info for a domain. It manages all aspects of user/domain interaction. A domain has one PDC and can have multiple BDCs. BDCs hold backup copies of the PDC's info and are occasionally synchronized with the PDC. Both PDCs and BDCs can perform some tasks like user authentication. Often, a main site will have a PDC and a BDC (which can share the PDC's load for certain tasks) and remote sites will BDCs to handle certain tasks locally
  • PDF
    Page Description Format: A file format by Adobe
  • perimeter network
    A network added between a protected network and an external network,in order to provide an additional layer of security. A perimeter network is sometimes called a DMZ.
  • Perl
    Practical Extraction and Report Language - An interpreted language developed by Larry Wall (, author of patch(1) and rn(1)) and distributed over Usenet. Superficially resembles awk, but is much hairier, including many facilities reminiscent of sed(1) and shells and a comprehensive Unix system-call interface
  • Permission Block
    This is part of the inode table's entries for each file and directory. The permission block can be shown for files and directores by using "ls -al" - the long output directory listing and is represented by 10 characters. The first character is a file type indicator differentiating between a file and a directory. The other nine characters refer to access permissions for the owner, group and world.
  • PGP
    Pretty Good Privacy - A high security RSA public-key encryption application for MS-DOS, Unix, VAX/VMS, and other computers
  • Photo CD
    A proprietary system developed by Kodak for storing photographic images from film onto CD-ROMs
  • Picons
    short for "personal icons". They're small, constrained images used to represent users and domains on the net, organized into databases so that the appropriate image for a given e-mail address can be found
  • Ping
    A network program which sends UDP packets to a host, and listens for responses. Used to check if a machine on the Internet is alive and reachable, and measure the Round Trip Time (RTT) between the local and remote host
  • pipe
    A programming device that lets you use the output of one process as the input of another. You must use a vertical bar (|) between two command invocations to indicate piping
  • pipe line
    a sequence of commands connected by pipes
  • Pipeline
    A sequence of programs through which a stream of data passes. Each stage or filter performs some operation on the data
  • policy independence
    A characterstic of the X window system in which windows can look and act any way the software developers want. This idea is the converse of the idea that, if all the windows on your screen look and act in a similar way, they will be easier for you to use
  • Port
    On the Internet, port often refers to a number that is part of a URL, appearing after a colon (:) right after the domain name. Every service on an Internet server listens on a particular port number on that server. Most services have standard port numbers, e.g. Web servers normally listen on port 80. Services can also listen on non-standard ports, in which case the port number must be specified in a URL when accessing the server
  • portable
    Pertaining to software that can be ported, or modified to run in another environment. Linux is an example of a portable system. Because all the programming that is hardware-specific is restricted to the kernel, a programmer can port Linux to a new computer system by changing only the kernel
    Portable Operating System Interface: a suite of applications program interface standards to provide for the portability of source code applications where operating systems services are required. POSIX is based on the UNIX (tm adminstrated by X/Open) Operating System, and is the basis for the X/Open specifications of The Open Group
  • PostScript
    A Page Description Language that gets its leverage by using a full programming language, rather than a series of low-level escape sequences, to describe an image to be printed on a laser printer or other output device (in this it parallels EMACS, which exploited a similar insight about editing tasks). It is also noteworthy for implementing on-the fly rasterization, from Bezier curve descriptions, of high-quality fonts at low (e.g. 300 dpi) resolution
  • PPD
    Postscript Printer Description specification. Adobe's spec of a standard virtual printer.
  • PPID
    the processes Parent PID, the creator of the process
  • PPP
  • PPPoE
    A technique for the encapsulation of PPP streams inside of Ethernet frames. This technology is being deployed by high-speed Internet access providers (cable modems, xDSL, etc.) in order to decouple the supply of bandwidth from ISP services.
  • PPTP
    Point-to-Point Tunneling Protocol - a networking technology that allows the use of the Internet as a secure virtual private network (VPN)
  • private key
    It contains encryption information and a fingerprint. It is generated locally on your system and should remain in a secure environment. If the private key is compromised, a perpetrator essentially has the code to your security system.
  • process
    An executing program. A process consists of the program code (which may be shared with other processes which are executing the same program), and some private data
  • process identifier
    An integer used by the Linux kernel to uniquely identify a process. PIDs are returned by the fork system call and can be passed to wait() or kill() to perform actions on the given process
  • process state
    the stage of execution that a process is in. It is these states which determine which processes are eligible to receive CPU time
  • protocol
    a set of rules that defines exactly how information is to be exchanged between two systems. This allows different types of machine to communicate in a form both understand
  • Proxy Servers
    a type of firewall that allows indirect internet access
  • ps
    displays information about your processes/jobs/programs which are running on the server
  • public-key encryption
    An encryption scheme, introduced by Diffie and Hellman in 1976, where each person gets a pair of keys, called the public key and the private key. Each person's public key is published while the private key is kept secret. Messages are encrypted using the intended recipient's public key and can only be decrypted using his private key
  • Python
    a scripting language that is designed notably clean, elegant, and well thought through

Key:  Commands - People - General

Last Updated Saturday, December 04 2004 @ 11:11 AM EST

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