. (dot) The current directory... (dotdot) The parent directory of the current directory.
absolute pathname A pathname which starts with the root directory (/). An absolute
pathname locates a file without regard to the working directory.
Pathnames that are not absolute are called relative.
access Frequently used to mean use, read from, or write to.
alias The mechanism for providing a different name for a Unix command string.
alphanumeric character One of the characters from a-z and 0-9, inclusive, either
uppercase or lowercase.
append To add to the end of something else.
argument Any word (string of characters delimited by spaces or tabs)
occuring after the command on a command line.
argv The variable in which the list of arguments to a command is stored.
argc Number of variables in the list of arguments to a command; only on some systems,
more usually referred to as $#argv
arithmetic operator Symbol used to indicate and execute addition (+), subtraction (-),
multiplication (*), or division (/).
a.out Binary executable file.
background job A job which is not receiving input from the terminal. A job not
in the background is said to be in the foreground.
bin directory A directory containing binaries of programs and shell scripts.
bit bucket Name for the file /dev/null. Characters written to this file are
thrown away; characters read from this file cause immediate EOF.
boot The loading of the kernel into memory.
BSD Berkeley Software Distribution, a version of Unix originating
at the University of California at Berkeley.
built-in command A command executed directly by the shell, as opposed to
forking a process to execute a file in a directory.
case sensitive Treating lower and upper case characters as two kinds of
characters with separate meanings.
child directory The directory below another directory in the file system tree structure.
child process A process created when a parent process forks a new process.
command A function performed by the system either by the shell or by a
program residing in a file in the directory.
command editing Modifying a previously entered command for reuse as a new command.
command prompt A string of characters that the system outputs to tell you it is
ready to accept the next command.
concatenate To link together in a series.
console The terminal with which you communicate to the system.
csh Shorthand for /bin/csh/, the C shell program.
current directory The directory to which commands refer by default, the
directory you are currently in. Same as working directory.
cwd Variable in the shell which holds the absolute pathname of
the current working directory.
daemon A continuously-running program which monitors and manages
a system resource such as printers, working sets, etc.
detached job A job that continues processing after the user has logged out.
device See physical device.
device file A file that represents a device. Also called a special file.
directory A Unix file that contains names of othe files or directories. More
technically, a system-managed file containing the associations
between path components and inodes. Each directory entry
contains an inode number and a path component.
directory hierarchy The arrangement of directories in a Unix file system, consisting
of a root directory at the top of the directory hierarchy
containing pointers to all file systems, and hence to all
directories on the system.
disk partition Part of a disk onto which a file system is mounted.
driver The device dependant code for a particular device class;
eg: a specific type of printer or terminal.
environment The set of characteristics describing a user's sessions, including
open files, user and group identification, process identification
and environment variables.
environment variable A variable exported automatically to subsequent programs.
EOF End-of-file generated by <ctrl-d> or the end of a file used as input.
escape A character (
) used to prevent the special meaning of a metacharacter.
ethernet A packetised asynchronous protocol using coaxial or optical fiber
cable with multiple senders and receivers. Each node listens for
packets which are addressed to it. When a node wants to send, it
waits for the ethernet to be idle and then sends. If two or more
nodes attempt to send at the same time, they detect this condition
by checking their own signals as they come back to the node and if
the signals are damaged each node waits for a short random
amount of time and then tries again.
event Past command stored in the history list.
exec A family of system calls that replace one program executing in
a process with another. The system calls differ in format of the
arguments and not in the purpose of the system call.
expansion The replacement of strings in the shell input which contain
metacharacters by other strings.
file A collection of data known to the operating system. In most
operating systems a file is associated with a specific name
or names. In Unix a file need not have a name but most files do
at least have one.
file descriptor The number Unix assigns to an open file.
filename The set of characters used to reference a file.
file system a) the component of the kernel that manages data resources into files
b) a disk data structure used to manage a tree of files.
filter A program that reads form standard input, does something and
writes to standard output.
foreground job A job that must be completed or interupted before the shell will
accept more commands; a job receiving input from the terminal.
See background job.
flag option Option used to modify the action of a command, consisting of
one or more letters preceded by the character -.
fork The system routine that creates a new process by duplicating the
calling (parent) process. One is called the parent and the other the
child. The parent process receives the process identification (pid)
of the child as a result of the fork system call. The child receives
from its copy of the same system call a pid of 0.
full-duplex the communications path is bi-directional and both ends may be
sending at the same time.
getty The terminal line monitoring program.
globbing Filename expansion using metacharacters.
group ID A numeric identification designating the group to which a user belongs.
half-duplex The communications path sends signals in one direction at a time.
The path may be capable of communicating in one direction only.
Otherwise, there is some agreed signal to allow the other end to
become the sender.
hidden file A file which begins with a period and often has special meaning
to the system.
history list The list of previously issued commands.
home directory Your default working directory; the location in the file system that
Unix automatically puts you when you log in. Same as the login directory.
host A computer network. Also known as a node.
ignoreeof A variable in some shells to prevent <ctrl-d> from logging
you out.
inode Pointer used to locate data on a physical device.
interrupt A signal to a program to stop execution (often set to <ctrl-c>).
job One or more commands typed on the same input line. Jobs are
classified as foreground, background, or suspended.
job number A unique number assigned to a job when it starts.
kernel The operating system control program.
ksh Shorthand for /bin/ksh, the Korn shell program.
link An entry in a directory that points to an existing file. There are
hard links and symbolic links (or soft links).
link the operation of linking object files and libraries together to form
an executable binary file.
.login A file in your home directory which is executed each time you login.
login directory Your default working directory; the location in the file system that
Unix automatically puts you when you log in. Same as the home directory.
login name The unique name assigned to a user which is used at the login
prompt to login to the system.
login shell The shell that is started when you login.
.logout A file in your home directory which is executed when you log out.
metacharacter Character with special meaning to the shell or to Unix.
NFS Network File System, a protocol developed by Sun Microsystems,
Inc, to permit access to files on remote computers.
noclobber A variable in some shells which can be set to prevent accidental
destruction of files by output redirection.
noglob A variable in some shells which can be set to suppress the
filename expansion of arguments containing certain metacharacters.
ordinary file Collection of characters stored on disk. Contrast with special
(device) file or directory file.
output Information that a program sends to the terminal or other file.
panic The kernel has detected a fatal error and is terminating a system
crash. A panic dump results.
parent directory The directory one level closer to the root than the current directory.
parent process The process that forked to create a child process.
path A directory specification. An absolute path starts with slash and is
relative to a process's definition of the system's root directory.
A relative path does not have an initial slash and is relative
to a process's definition of its current working directory.
pathname A list of directories, separated by / characters. It is used to trace
a path through a file structure to locate a file. The types are
simple, absolute and relative.
path component A field of a path delimited by the beginning, a slash, and the end of
the path.
physical device A piece of hardware attached to the computer eg: disk drive, printer.
physical device name The name given to a physical device.
PID Process IDentification. The PID number is a unique number
assigned to each process when it is initiated.
pipe A connection between two programs such that the standard
output of one is connected to the standard input of the other.
pipeline A group of programs connected by pipes.
plain file A file used to store a program, text or other data, as contrasted
with directory file or device file.
port The part of a computer system to which a terminal is connected.
prompt A cue from a program, usually displayed on the terminal, indicating
that it is waiting for input.
process The unit of work, or the means by which Unix executes a program.
process id An integer that uniquely identifies a process within the system.
quotation The process by which metacharacters are prevented from using
their special meaning, usually by using the character ' in pairs
or by using the character
.
redirection The routing of input or output from or to a file, rather than a terminal.
relative pathname A pathname which does not begin with a / is interpreted relative to
the current working directory. Contrast with absolute pathname.
RISC Reduced Instruction Set Computer.
root Another name for the superuser; the source directory of the file system.
root directory The directory which is at the top of the entire directory structure and the start of
an absolute pathname. Represented by a /
script A sequence of shell commands placed in a file/program.
sh Shorthand for the file /bin/sh, the Bourne shell program.
shell A command language interpreter.
shell script See script.
signal A short message sent to a running program which causes
something to happen to that process.
socket Defines an endpoint for network communication (BSD only).
special character See metacharacters.
special file A file that represents a physical device. Also called a device file.
spooler A program or system of programs that accepts files to be delivered
to a system resource that needs to be used serially, eg: printers or
communications equipment.
standard error output A file that a program can receive output to, usually reserved for
error messages. By default it is directed to the terminal.
standard input A file that a program can receive input from. By default, it comes
from its terminal.
standard output A file to which a program can send output. By default, it is to the terminal.
stream Same function as socket (System V).
superuser A priviledged user who can perform administrative tasks.
suspended job A job which has received a stop signal, either via <ctrl-z> or
the stop command.
symbolic link A method to associate a file with two or more file names.
system call A request for services from the operating system control program or kernel.
TCP/IP A communication protocol that may be embedded within a
physical communications protocol such as Ethernet that supports
methods of communications that are sending letters called
datagrams or establishing two-ways links called virtual circuits.
Datagrams may arrive out of order or be lost. Virtual circuits protect
against packets arriving out of order but may lose packets. Higher
order protocols may provide either order services or replacements
for lost or damaged packets.
trusted host A host that permits access without a password.
tty An abbreviation for teletype, frequently used to indicate the port
to which a given terminal is connected.
user ID A number associated with each login name.
white space A name for spaces and/or tabs.
wild card character A character with a special meaning in a file specification.
working directory The directory you are currently in. Relative pathnames are built
upon the working directory. Also called current directory.