P

Parent Directory
Identified by two dots (..), this is the directory immediately above a subdirectory. Each subdirectory has only one parent, but a parent directory can have many subdirectories. The /home directory contains the user's directory. The /etc directory contains system administration files, such as the passwd and hosts files. The /opt directory contains unbundled and third-party software applications. The /usr directory contains executable commands, system administration utilities, and library routines.

Password
A code, word, or set of characters used as a security measure against unauthorized access to data. It enables a user to access a file, computer, or program.

Pathname
The directory hierarchy of the location where a file is stored.

PC
Short for personal computer. It can also stand for printed circuit.

Permissions
The set of identifiers that control access to files. Permissions consist of three fields: user, group, and world. The user field controls access by the user owning the file, while the group field controls access by anyone matching the file's group specification. As the name implies, the world field controls access by everyone else. Each field contains the same set of bits that specify operations that may or may not be performed, such as reading, writing and executing. The sticky bit is a fourth permission that can be set. This allows the world to have access to a file but only the user can move or delete it.

PID
Process IDentification. A temporary number assigned by the operating system to a process or service.

Ping
A network command used to find out if a hostname is valid and that the machine associated with that hostname is in fact operational and in the domain. It works by sending a packet to the specified address and waiting for a reply.

Pipe
A temporary software connection between two programs or commands. The pipe ( | ) takes the output of one command and passes it as input into a following command. Pipes actually allow you to build a minature program. You must always have a command on each side of a pipe.

Primary Memory
Please see Random Access Memory.

Print
In computing, to send information to a printer where a paper copy can be created.

Printer Queue
A buffer for documents and images waiting to be printed. When an application places a document in a print queue, it's held in a special part of the computer's memory, where it waits until the printer is ready to receive it.

Process
An instance of a program in execution. Linux allows many processes to be in execution at the same time and many processes to be executing the same program. It is possible for a process to switch from program to program.

Programs
Also known as utilities. An organized list of instructions that tells the computer what to do. Program, software, and instructions are synonymous.

Prompt
A symbol on a display screen indicating that the computer is waiting for input.