Files and processes

Everything in UNIX is either a file or a process.

A process is an executing program identified by a unique PID (process identifier).

A file is a collection of data. They are created by users using text editors, running compilers etc.

Examples of files:

• a document (report, essay etc.)


• the text of a program written in some high-level programming language


• instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);


• a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.