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Glossary of Unix Terms

The following is a list of commonly used Unix terms and symbols and their definitions when used in the context of SuperCloud.


The root directory.


Pronounced "tilde". Shorthand expression representing a user's home directory. On the SuperCloud, ~ refers to /home/gridsan/<username>. When using tilde in a pathname, it must be the first character. For example, ~/test/test.txt.


Pronounced "dot". Shorthand expression representing the current working directory


Pronounced "dot-dot". Shorthand expression representing the parent directory of the current working directory

absolute pathname or full pathname

A pathname that begins at the root directory. For example, /home/gridsan/groups.

background process

A process that runs without interfering with normal command line entry. A process runs in the background when the command to start the process is issued with an ampersand & character at the end of the command.


A file whose contents are in binary (non-text) format, and contains compiled source code. Binary files can be, but are not necessarily executable (for example, library files).

child process

A process that was created by another process, the parent process.

current directory, current working directory, or working directory

The user's current directory; the directory where a file is read or written when a directory path is not included in the name of the file. When specifying a pathname, a shorthand for the current directory is the dot . character.


A type of file that contains names and information about other files or other directories. This is the Linux equivalent of Windows folders.


The set of conditions under which a user is working on the computer.

environment variable

Environment variables allow you to customize the environment in which programs run. They become part of the environment in which the programs run and can be queried by running programs and any of its child processes.


A file that can be executed from the command line by entering the name of the file as the command. The file's "executable" permissions flag must also be set. An executable file can be, but is not necessarily a binary file (for example, a script).

file system

The collection of files and file management structures on a mass storage device.

foreground process

A process that must complete or be interrupted before control is returned to the command line.


The command used for searching files for lines containing characters that match specified strings or patterns (regular expressions) and writes the matching lines to standard output.


For SuperCloud purposes, a group is a set of users that share access to protected resources.

hidden file

A file whose name begins with a period (for example, .bash_profile). By default, the ls command does not include these files in its listings. Use ls -a to see hidden files in the file listing.


An environment variable containing the full pathname to your home directory.

home directory

A directory that is where a particular user's personal files reside. A home directory is also called a login directory because when you log into the system, your current work directory is your home directory. When specifying a pathname, a shorthand for a user's home directory is the tilde ~ character.


To stop the operation of a process. In most cases, a user can kill a foreground process by pressing ctrl-c.


A tool that builds applications/executables from source files.


An interface to the online reference manuals. The manarg command will display the manual page for the given argument.

parent directory

The directory in which another directory resides. When specifying a pathname, a shorthand for the parent directory is dot-dot ... A directory that is contained in the parent is called a subdirectory.

parent process

A process that has created other processes (its children processes). In Unix, every command that isn't a built-in command creates a child process.


An environment variable containing the user's search path for commands.


An ordered list of directories that the shell searches for executables that are not built-in commands and are not entered with a pathname.


The name of a file, concatenated onto a list of the directories that must be accessed to get to the file. Absolute pathnames begin at the root directory and are written with an initial slash (for example, /home/gridsan/myusername/test/myfile.txt). Relative pathnames begin at the user's working directory and are written without the initial slash (for example, test/myfile.txt).


The constraints placed on a file to control what users or groups may read, write, or execute the file. There are three sets of permissions: those applied to the owner of the file, those applied to the owner's group, and those applied to everyone else, called "other."


A command that lets you use two or more commands, sending the output of one command to serve as the input to the next command. A pipe is represented as the symbol "|".


An independent computation running on a computer. Processes have their own address (memory) space and may create threads that will share their address space. Processes must use interprocess communication to communicate with other processes.

process id or pid

A unique number assigned to a process that is running.


A feature that allows you to change where standard input, standard output and/or standard error are sent during execution of a command.

regular expression, regex, or regexp

A pattern of one or more characters used to search data and matching complex patterns. Regular expressions are similar to wildcards, but more powerful. You can find an introduction to regular expressions here.

relative pathname

A pathname that begins at the user's working directory; it is written without the initial /. For example, docs/myfile.txt


The login name for the superuser (system administrator). Also the name of the topmost directory in the file system, represented by the slash / character.


A text file that is executed by the specified shell, as indicated by the first line of the script (for example, #!/bin/bash).

search path

A list of pathnames (usually separated by colons) of directories to be searched for executable files and other kinds of files. You can create search paths by defining environment variables such as $PATH, $PYTHONPATH, $LD_LIBRARY_PATH.


A command-line Interface between a user and the kernel. The shell accepts and interprets your commands to run programs, work with file systems, manipulate text files, etc.

standard error or stderr

The file where programs write error messages. The standard error file is a virtual file that is by default assigned to the user's screen but can be redirected to any file available to the user.

standard input or stdin

The file where programs receive input data or commands. The standard input file is a virtual file that is by default assigned to the user's keyboard but can be redirected to any file available to the user.

standard output or stdout

The file where programs write output data. The standard output file is a virtual file that is by default assigned to the user's screen but can be redirected to any file available to the user.


A directory that is contained within another directory. The containing directory is called the parent directory.

A type of file that points to another file or directory on the system. Symlinks are similar to shortcuts in Windows.