UNIX_Concepts

1. GPL: General Public License. (Stallman, GNU)
2. DISTRO: Linux DISTRIBUTION
3. TCO: Total Cost of Ownership.
4. CLI: Command Line Interface,  (GUI).
5. Runlevel: a runlevel is a system software configuration that allows a specified group of process to exist. A runlevel specifies which fundamental services UNIX will provide.
6. ring buffer: a buffer of a fixed size for which any new data added to it overwrites the oldest data in it.
7. tty: print the file name of the terminal connected to standard input. pwd: print working directory.
8. stty can be used to display or change the setting of your terminal. getty can be used to open communication with a terminal and start the login process.
9. TERMCAP database: a system for managing the display screen of various types of terminal. curses: a programming interface to carry out the functions that was necessary to manage a screen display. TERMINFO: is a library and database that enables programs to use display terminals in a device-independent manner. ncurses: a programming library that provides an API which allows the programmer to write text-based user interfaces in a terminal-independent manner. TERMINFO data is compiled, to see use infocmp command($ infocmp vt100 | less) 
10. 4 types of terminal: xterm(Mac OS X), VT220, VT100, 3270; a global environment TERM whose value is set to the type of terminal you are using. $ echo $TERM, $ printenv: display the values of all the environment varibles within your shell.
11. ^: caret, short for Ctrl key.
12. standard input: data typed at the keyboard is treated the same as data read from a file.
13. UNIX marks the end of each line with a ^J(newline, \n, 0x0a, 10(decimal)) character, Windows marks each line with a ^M^J(\r\n), Mac ends with a ^M(\r, 0x0D, 13(decimal)).
14. RPN: Reserve Polish Notation
15. FUBAR: fuc.k.ed up beyond all recognition. used to describe a truly messed up situation
16. foo, bar, foobar: In the world of UNIX and on the Internet, they are commly used as generic terms to represent unnamed items within a discussion or exposition.
17. SHELL: command processor; script interpreter.
18. POSIX: a large set of specifications, a blueprint for standardizing operating systems.(a project to standardize Unix). "Portable Operating System Interface".
19. BASH: "Bourne again shell".
20. Symbolic link(soft link): A symbolic link, also termed a soft link, is a special kind of file that points to another file, much like a shortcut in Windows or a Macintosh alias. Unlike a hard link, a symbolic link does not contain the data in the target file. It simply points to another entry somewhere in the file system. This difference gives symbolic links certain qualities that hard links do not have, such as the ability to link to directories, or to files on remote computers networked through NFS. Also, when you delete a target file, symbolic links to that file become unusable, whereas hard links preserve the contents of the file. 

    To create a symbolic link in Unix, at the Unix prompt, enter:

    ln -s source_file myfile

    Replace source_file with the name of the existing file for which you want to create the symbolic link (this file can be any existing file or directory across the file systems). Replace myfile with the name of the symbolic link. The ln command then creates the symbolic link. After you've made the symbolic link, you can perform an operation on or execute myfile, just as you could with the source_file. You can use normal file management commands (e.g., cp, rm) on the symbolic link.

21. "\": use as continuation in the end of a line
22. UUID: The intent of UUIDs is to enable distributed systems to uniquely identify information without significant central coordination. In this context the word unique should be taken to mean "practically unique" rather than "guaranteed unique". Since the identifiers have a finite size, it is possible for two differing items to share the same identifier. The identifier size and generation process need to be selected so as to make this sufficiently improbable in practice. Anyone can create a UUID and use it to identify something with reasonable confidence that the same identifier will never be unintentionally created by anyone to identify something else. Information labeled with UUIDs can therefore be later combined into a single database without needing to resolve identifier (ID) conflicts.
23. Newline characters:
    • Unix, Linux-based: LF(Line feed, '\n', 0x0A, 10 in decimal)
    • Windows: CR(Carriage return, '\r', 0x0D, 13 in decimal)+LF, that is '\r\n'
24. sandbox: In computer security, sandbox is a security mechanism for separating running programs. Sandboxing technology is frequently used to test unverified programs which may contain a virus or other malignant code, without allowing the software to harm the host device.
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