CS35L/firstLabNotes.txt at master · DevYanB/CS35L · GitHub

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What is open source software:
- Source Code is publically available
- Anyone can modify

Open Source Operating Systems (Os's):
- Kernel: Core of operating system (Abstraction of hardware!)
	- Allocates time and memory to programs
	- Handles the file system and communication b/t soft and hardware
- Shell: Interface between user and the kernel
	- Interprets commands user enters
	- Takes action to enable and cause commands to be executed
- Programs

Command Line Interface (CLI):
- Steep Learning curve
- Pure control
- Cumbersome multitasking
- Convenient remote access
- Faster performace and uses less resources

Graphic User Interface (GUI):
- Ease of use and intuitive
- Easy multitasking
- Bulky remote access
- Slower
- Uses more resources

//==========================================================

SHELL BASICS:

<up arrow>: previous command

<tab>: auto complete

cd ../: is going into the upper level in the folder hierarchy

~: is home directory (can set to whatever)

pwd: print working directory

cd: change directory
- ~ :home
- . :current dir
- / :root directory or separator
- .. :parent directory

mv: move/rename file

cp: copy a file

rm: remove a file
- r flag: directory

mkdir: make a directory

ls: display files and directoried in current directory
- d flag: only list directories
- a flag: list all files including hidden ones
- l flag: show long listing including permissio ninfo
- s flag: show size of each file in blocks

sudo: execute command as master user

ln: create link
- hard links: to physical data (direct point to data; immune to changes since direct to data)
	- A normal file is considered as a hard link to data, so with a file default will be 1 hard link
- symbolics links to file (-s) (points to file that points to data; changing original messes up soft link)

touch: update access and modify time to current time
- touch filename
- touch -t 201101311759.30 filename (set access and modification time to 2011 January 31 time 17:59:30)

cat: shows contents of a file

find: finds a file and return the path of the target file
- -name: name of the file
- -perm: permission of a file
- -user: owner of a file
- -maxdepth: hoe many levels to search

RegExp: find . -name "file1*" if you only know the file1 part of the filename (* is like a placeholder in regex)

Man: manual page
- hit q to exit

------------------------------------------------------------------------------------------------------------------
LINUX FILE PERMISSIONS:

Ordering of Permissions:
next 3 are user permissions
next 3 are group permissions
last 3 are for everyone else
Then number of hard links
User name
group name
size
date/time last modified
filename
R: readable
W: writeable
E: executable

chmod: add permissions to a file; chmod to a file affects the hard link permissions as well, not soft link's though...
Each digit corresponds to the 3 sections of permission: user, group, other (___):
- 0: nonde
- 1: execute only
- 2: write only
- 3: write and execute
- 4: read only
- 5: read and execute
- 6: read and write
- 7: full

//==========================================================

Everything is either a file or process
- Process: an executing program identified by PID
- File: collection of data
	- Document
	- Text of program
	- Executable
	- Directory
	- Devices

Libraries and such will go to other top leverl directories

Absolute vs. Relative Path:
- Absolute path is always from root
- Relative path is from what directory we are in