Sources: mostly Wikipedia or Unix basics guides, or as given

>>Definitions, etc.

tty	TeleTYpwriter
general term for computer terminal, whether physical (teleprinter) or
electronic (monitor)

tar	Tape ARchive
Files archived with tar are called "tarballs".

root	admin 

sh	shell - user interface, i.e.: 
	Command-Line Interface (CLI) or
	Graphical User Interface (GUI)
	
ssh secure shell

~	home folder

/	root folder

$	in terminal: logged in as standard user (regular privileges)
e.g., [user@localhost ~]$

.   hidden files or directories start with a period

dotfile     hidden-by-default file storing configuration settings 
(e.g., .bashrc)

rc	Run Commands

localhost   name of computer

swap	move memory between RAM and disk

inode   index node
Data structure storing information about files and directories (metadata, owner, permissions, location on disk, etc.)

ioctl   input/output control

errno   error number

Unix time: number of seconds since the Unix epoch (00:00:00 UTC, 1 Jan 1970). (Note however that occasional leap seconds have been inserted).

/dev/null
The "null device"; a folder that deletes everything sent/moved to it

Daemon
A computer program that runs as a background process. Unix daemons typically have a process name ending with d. 

Binaries 
Compiled versions of executable programs.

Mask
Data used for bitwise operations (operations on individual bits).

Pipe (|)
Use the output of one program or command as the input to another: 
A | B

(http://www.ee.surrey.ac.uk/Teaching/Unix/unix3.html)

Redirect (>)
Redirect the input or output of a command: 
A < B	use contents of file B as input to command A
A > B	place output of command A in file C

(http://www.ee.surrey.ac.uk/Teaching/Unix/unix3.html)

./script_name.sh    run script_name script

&   run process in background 
(placed at end of command invoking process)

\   escape character in Bash

>File extensions
.d      directory
.c      C/C++ source code
.h      header file (C/C++)
.sh     shell script
.conf   config file

.tar    file archived with tar
.gz     file compressed with gzip
.xz     file compressed with xzip
The modular nature of Unix utilities means files can be archived and compressed separately; this is indicated by the extension .tar.gz (or .tar.xz).

>Utilities
cron    job scheduler
(from Greek "chronos", "time")

init    initialization
First process (PID 1) run during startup

>>Filesystem

>Directory hierarchy
/       root

.       current directory
..      parent directory

/bin    binaries of user utilities (like ls and cp)    
/boot   files needed for boot
/dev    devices
/etc    system-wide configuration files and system databases
/home   user home directories - personal files and documents
/lib    libraries  
/media	mount point for removable media		
/mnt    mounted devices
/opt    optional add-on packages (user-installed software)
/proc   processes
/run	temporary data from system processes
/root   root user's home folder
/sbin   system (superuser) binaries
/srv    servers
/sys    system (kernel and device/driver) information from sysfs
/tmp    temporary files not preserved on reboot
/usr    user files
    /bin        binaries  
    /include    headers
    /lib  	libraries
    /local	local software
    /share  	architecture-independent shareable program data
/var    variable - files that may change often
    /log	system log files
    /mail	incoming mail
    /spool 	spool (data copied between different devices)
    /src	source - uncompiled source code
    /tmp 	temporary files to be preserved on reboot

>File permissions
File permissions are managed by class and mode.

Class: the class of users to whom the permissions belong.
user	the owner of the file	
group	users who are members of the file's group
other	users who are neither the fileowner nor filegroup members 

Mode: the permissions available to a class.
Read 	read file or list directory contents 
Write	write to file or directory
eXecute	execute file or recurse directory tree

Numerical notation in octal or binary is also used:
read    4   100
write   2   010
execute 1   001

File permissions are listed in the file mode string:
-rwxrwxrwx

The first letter indicates the file type:
    d   directory
    -   regular file
    l   symbolic link
    p   FIFO (named pipe)
    s   socket
    c   character device
    b   block device

Class permissions are then listed in the order of user, group, other. A hyphen indicates that the class does not possess the requisite permission.

File permissions can be edited using the chmod command, with the syntax:
    chmod [class][operator][mode] file
	class: (u)ser, (g)roup, (o)ther
	operator: +	add
		  -	subtract
		  = 	make exact
	mode: (r)ead, (w)rite, e(x)ecute
	file: the file to be modified

The umask command can be used to determine how permissions are set for newly created files.

>File attributes [explain]
setuid/SUID (set user ID)
setgid/SGID (set group ID)
sticky bit

>>Background

>"Unix philosophy"
The UNIX philosophy is documented by Doug McIlroy in the Bell System Technical Journal from 1978:
1.  Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new "features".
2.  Expect the output of every program to become the input to another, as yet unknown, program. Don't clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don't insist on interactive input.
3.  Design and build software, even operating systems, to be tried early, ideally within weeks. Don't hesitate to throw away the clumsy parts and rebuild them.
4.  Use tools in preference to unskilled help to lighten a programming task, even if you have to detour to build the tools and expect to throw some of them out after you've finished using them.

It was later summarized by Peter H. Salus in A Quarter-Century of Unix (1994):
    Write programs that do one thing and do it well.
    Write programs to work together.
    Write programs to handle text streams, because that is a universal interface.
	
In their award-winning Unix paper of 1974, Ritchie and Thompson quote the following design considerations:
    Make it easy to write, test, and run programs.
    Interactive use instead of batch processing.
    Economy and elegance of design due to size constraints ("salvation through suffering").
    Self-supporting system: all Unix software is maintained under Unix.

https://en.wikipedia.org/wiki/Unix_philosophy#Origin

>"Everything is a file"
Everything is a file describes one of the defining features of Unix, and its derivatives—that a wide range of input/output resources such as documents, directories, hard-drives, modems, keyboards, printers and even some inter-process and network communications are simple streams of bytes exposed through the filesystem name space.

https://en.wikipedia.org/wiki/Everything_is_a_file



>>Names (acronyms)

>Unix
The origins of Unix date back to the mid-1960s when the Massachusetts Institute of Technology, Bell Labs, and General Electric were developing Multics, a time-sharing operating system for the GE-645 mainframe computer. Multics featured several innovations, but also presented severe problems. Frustrated by the size and complexity of Multics, but not by its goals, individual researchers at Bell Labs started withdrawing from the project. The last to leave were Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna, who decided to reimplement their experiences in a new project of smaller scale. This new operating system was initially without organizational backing, and also without a name.

The new operating system was a single-tasking system. In 1970, the group coined the name Unics for Uniplexed Information and Computing Service (pronounced "eunuchs"), as a pun on Multics, which stood for Multiplexed Information and Computer Services. Brian Kernighan takes credit for the idea, but adds that "no one can remember" the origin of the final spelling Unix. Dennis Ritchie, Doug McIlroy, and Peter G. Neumann also credit Kernighan. 

https://en.wikipedia.org/wiki/Unix#History

>POSIX: Portable Operating System Interface
>MINIX: mini-Unix
>Linux: Linus [Torvalds] + MINIX

>Bash
The shell's name is an acronym for Bourne-again shell, a pun on the name of the Bourne shell that it replaces and on the common term "born again".

https://en.wikipedia.org/wiki/Bash_(Unix_shell)

>curses: pun on "cursor optimization" 

https://en.wikipedia.org/wiki/Curses_(programming_library)



>Command meanings/definitions
ar	archiver

awk	authors Alfred Aho, Peter Weinberger, Brian Kernighan

bg	background
Run jobs in background

cat	concatenate
Write files to standard output

cc	C compiler

cd	change directory
	
chmod	change mode (= file permissions)

chroot  change root directory for a process

cp 	copy

dd	data definition
Convert and copy files
(https://en.wikipedia.org/wiki/Dd_(Unix)#History)

df	disk free
Display available disk space

diff	
Display differences between two files

du	disk usage
Estimate file system usage

ed  	[text] editor

emacs   Edit MACroS

fg	foreground
Run jobs in foreground

fsck	File System Consistency checK

grep    ed command g/re/p (Globally search REgular expression and Print matching lines)

ln	link
Create links between files

ls	list
List files in a directory

man	manual

mv	move
Move or rename files

ps	process status

pwd	Print Working Directory

rm	remove
Delete files

roff	RunOFF

sed	Stream EDitor

sh	shell

su	substitute sser

sudo	superuser do

tar	tape archiver

top	table of processes

vi  visual