Linux Filesystem Hierarchy

Glossary
ARPA
The Advanced Research and Projects Agency of the United States Department of Defense. Also
known as DARPA (the "D" stands for "Defense"), it originated in the late 1960s and early 1970s the
proposal and standards for the Internet. For this reason, the Internet was initially referred to as
ARPANet, and connected the military with the various centers of research around the United States in
a way that was intended to have a high degree of survivability against a nuclear attack.
BASH
The Bourne Again Shell and is based on the Bourne shell, sh, the original command interpreter.
Bourne Shell
The Bourne shell is the original Unix shell (command execution program, often called a command
interpreter) that was developed at AT&T. Named for its developer, Stephen Bourne, the Bourne shell
is also known by its program name, sh. The shell prompt (character displayed to indicate readiness for
input) used is the $ symbol. The Bourne shell family includes the Bourne, Korn shell, bash, and zsh
shells. Bourne Again Shell (bash) is the free version of the Bourne shell distributed with Linux
systems. Bash is similar to the original, but has added features such as command line editing. Its name
is sometimes spelled as Bourne Again SHell, the capitalized Hell referring to the difficulty some
people have with it.
CLI
A CLI (command line interface) is a user interface to a computer's operating system or an application
in which the user responds to a visual prompt by typing in a command on a specified line, receives a
response back from the system, and then enters another command, and so forth. The MS−DOS
Prompt application in a Windows operating system is an example of the provision of a command line
interface. Today, most users prefer the graphical user interface (GUI) offered by Windows, Mac OS,
BeOS, and others. Typically, most of today's Unix−based systems offer both a command line
interface and a graphical user interface.
core
A core file is created when a program terminates unexpectedly, due to a bug, or a violation of the
operating system's or hardware's protection mechanisms. The operating system kills the program and
creates a core file that programmers can use to figure out what went wrong. It contains a detailed
description of the state that the program was in when it died. If would like to determine what program
a core file came from, use the file command, like this: $ file core That will tell you the name of the
program that produced the core dump. You may want to write the maintainer(s) of the program,
telling them that their program dumped core. To Enable or Disable Core Dumps you must use the
ulimit command in bash, the limit command in tcsh, or the rlimit command in ksh. See the appropriate
manual page for details. This setting affects all programs run from the shell (directly or indirectly),
not the whole system. If you wish to enable or disable core dumping for all processes by default, you
can change the default setting in /usr/include/linux/sched.h. Refer to definition of INIT_TASK, and
look also in /usr/include/linux/resource.h. PAM support optimizes the system's environment,
including the amount of memory a user is allowed. In some distributions this parameter is
configurable in the /etc/security/limits.conf file. For more information, refer to the Linux
Administrator's Security Guide.
daemon
A process lurking in the background, usually unnoticed, until something triggers it into action. For
example, the \cmd{update} daemon wakes up every thirty seconds or so to flush the buffer cache, and
the \cmd{sendmail} daemon awakes whenever someone sends mail.
DARPA
The Defense Advanced Research Projects Agency is the central research and development
organization for the Department of Defense (DoD). It manages and directs selected basic and applied
Glossary
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research and development projects for DoD, and pursues research and technology where risk and
payoff are both very high and where success may provide dramatic advances for traditional military
roles and missions.
DHCP
Dynamic Host Control Protocol, is a protocol like BOOTP (actually dhcpd includes much of the
functionality of BOOTPD). It assigns IP addresses to clients based on lease times. DHCP is used
extensively by Microsoft and more recently also by Apple. It is probably essential in any
multi−platform environment.
DNS
Domain Name System translates Internet domain and host names to IP addresses. DNS implements a
distributed database to store name and address information for all public hosts on the Net. DNS
assumes IP addresses do not change (i.e., are statically assigned rather than dynamically assigned).
The DNS database resides on a hierarchy of special−purpose servers. When visiting a Web site or
other device on the Net, a piece of software called the DNS resolver (usually built into the network
operating system) first contacts a DNS server to determine the server's IP address. If the DNS server
does not contain the needed mapping, it will in turn forward the request to a DNS server at the next
higher level in the hierarchy. After potentially several forwarding and delegation messages are sent
within the DNS hierarchy, the IP address for the given host eventually is delivered to the resolver.
DNS also includes support for caching requests and for redundancy. Most network operating systems
allow one to enter the IP addresses of primary, secondary, and tertiary DNS servers, each of which
can service initial requests from clients. Many ISPs maintain their own DNS servers and use DHCP to
automatically assign the addresses of these servers to dial−in clients, so most home users need not be
aware of the details behind DNS configuration. Registered domain names and addresses must be
renewed periodically, and should a dispute occur between two parties over ownership of a given
name, such as in trademarking, ICANN's Uniform Domain−Name Dispute−Resolution Policy can be
invoked. Also known as Domain Name System, Domain Name Service, Domain Name Server.