This section covers most of the useful commands available on any UNIX operating system. None of the commands are covered in great detail, but enough information is given to be a useful introduction for those not familiar with the various UNIX commands. For more details on these and other commands, there are two standard commands for getting documentation on programs installed on the system: the man command and the info command. If information is desired for command foo, either man foo or info foo will provide the available documentation. Not all packages provide info pages, while many GNU packages don't provide man pages. Depending on the program involved one or the other of these will be available. When the command is unknown but some idea of functionality is known, a key word search can be made of the man pages using the apropos command or man -k.
Note: The term program and command have been used interchangeably in the previous discussion. This is because in UNIX, all executable commands are, in fact, programs that execute to perform their various tasks. Every program, and thus, every command, is documented in some fashion or another within the system. In a Debian system each package places its copyright, changelogs, and any additional examples or documents into the directory /usr/share/doc/<package name> and is a good place to start after you have exhausted the man and info pages.