Merge pull request #2 from pcudd33/pcudd33-patch-2

The finalized version of Day2Notes. All naming conventions are followed and all information from the lecture notes was added with detail.

Author: pcudd33

Day2Notes

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+# **Lecture 2**
+
+## Class presentations
+
+ ### Problems caused by issues in software
+#### Northeast Blackout of 3003
+- There was a software bug called the “Race Condition”, that once triggered stalled FirstEnergy’s control room alarm system for over an hour. System operators were unaware of the malfunction
+- Loss of water pressure led to water contamination. So, 4 million people were under boil water advisory until August 18th. 4 Days after the power outage.
+- Power outage along the eat coast. 55 Million people were affected during this and 100 people died.
+- “A race condition occurs when two threads access a shared variable at the same time...” – Microsoft. “in some homes, there are multiple light switches connected to a common ceiling light. When these types of circuits are used, moving either switch from its current position turns the light off.” – tech target
+
+#### Aviation – 737 MAX
+-	##### Software MCAS – maneuvering characteristics augmentation system
+o	Built to enhance pitch stability of 737 MAX so that it would work like older models (newer models had bigger engines which pushed nose up)
+o	Meant to make it easier to train flight crews on newer models 
+o	Flight crews not well trained on use
+-	##### Issue Caused by false AOA inputs to 1 sensor which triggered MCAS (tipped nose down during takeoff and kept malfunctioning as crew tried to correct nosedive because they could not override the software).
+o	AOA – angle of attack (angle between wing and airflow on the wing)
+o	2 crashes, 346 people died
+-	##### Changes MCAS software has been modified to use 2 sensors instead of 1 (in case one fails), and flight crew can now completely override the software.
+o	Pilots now go through training on managing MCAS and problems that might arise
+
+#### ETCS software malfunction
+-	During the trial embedded systems expert who reviewed Toyota’s electronic throttle source code testified that they found Toyota’s source code defective, and that it contains bugs – including bugs that can cause unintended acceleration.
+-	“we’ve demonstrated bow as little as a single bit flip can cause the driver to lose control of the engine speed in real cars due to software malfunction that is not reliably detected by any fail-safe.” Michael Barr, CTO, and co-founder of Barr Group told us in an exclusive interview. Barr served as an expert witness in this case.
+
+#### Ariane 5 flight 501
+-	Problem came from reused code from the inertial reference platform (IRS) on the Ariane 4
+-	Ariane 5’s flight path caused certain values, specifically the horizontal bias variable to be much higher than the code was meant to handle.
+-	Greater values of horizontal bias data were converted from 64-bit floats to 16-bit int values causing an overflow, meaning the numbers were too large to represent with just 16 bits.
+-	Only 4 of the 7 variables used were protected from overflow, designed only to handle the assumptions about the Ariane 4 flight path. 
+-	The overflow halted the IRS modules, and the one active module send a diagnostic bit patter to the on-board computer, bit it was interpreted as flight data. 
+-	This caused the rocket to bank to an angle of more than 20 degrees, causing it to rip apart and then self-destruct.
+-	Supplier of the nav software was told to stop the processor when an exception occurred, so the exception which occurred was due to a flaw in the design, causing the shutdown of two good units when they could have still provided best estimates of the required info. 
+o	Simulations should have been completed prior to launch
+o	Identify all previous assumptions and make sure they are still valid
+o	Ranges of variables should have been explicitly quantified instead of just assuming a range, in this case a 16-bit range
+-	The failure brough to light the risk with complex computation and increased the support for research on ensuring the reliability of safety critical systems.
+
+#### Patriot Missile defense system error
+-	 ##### What happened
+o	Failed to intercept an incoming missile. 
+o	The incoming missile hit a United States Army Barracks in Dhahran, Saudi Arabia during the Gulf war.
+-       ##### How was SW involved
+o	Source Code Reviews after incident revealed errors.
+o	Software calculated the position of the incoming missile.
+o	Failure due to rounding error over 100 hours.
+-	##### Why so Bad
+o	28 Americans killed, over 100 injured.
+o	This flaw exists in ALL Patriot missile Defense Systems.
+o	Purely software, completely preventable.
+-	 ##### Implications
+o	Now this type of software undergoes endurance tests (what happens if we run this code for a long time).
+
+
+
+
+## Class Notes
+	
+### Using a computer
+
+#### Graphical User Interface
+	- GUIs are convenient, but slow.
+
+#### Command line access
+	- gives us access to run tools “under the hood”.
+	- can increase productivity by learning these command line tools.
+
+#### Linux based OS
+             - Windows makes up 75% of all desktop/laptop operating systems
+             - MacOS makes up 15% of all desktop/laptop operating systems			
+             - We will focus on a Linux-based OS for learning a set of tools				
+             - Linux is the dominant OS
+
+#### Sshing and other definitions
+	- We will use virtual servers running Linux for this class
+
+	#### Definition
+**Shell** is a program that exposes an OS’s services to a human user or other programs
+- textual interface (terminal, git-bash, PowerShell)
+	#### Definition
+		**Secure Shell** remote access to a shell on another computer
+
+	###### how to ssh
+		- the xx is each student’s unique number
+		- cslinuxlab-xx.stlawu.local
+
+#### Using terminal on the secure shell
+
+	###### Logging into Linux labs
+		- ssh {full email address}@cslinuxlab-xx.stlawu.local
+		- type yes
+		- enter your St. Lawrence password     
+		- Control d to exit Linux labs 
+
+	###### Creating password 
+		- ‘ssh-keygen -o’ Generating public/private rsa key pair
+		- hit enter
+		- chose passphrase
+		- type It again
+		- Your certificate is created
+
+	###### Using a certificate
+		- ‘ssh-copy-id’ {full email address}@cslinuxlab-xx.stlawu.local 
+			- this is how you get your public key onto the other machine
+	
+-	Enter your passphrase
+-	Now your certificate is on the Linux lab machine
+
+#### Basic bash commands
+	- ‘pwd’ (present working directory)
+- ‘ls’ (list all files/directories/etc.)
+- ‘cd’ (change directory)
+	- ‘cd .’ (stay in that level)
+	- ‘cd ..’ (takes you up one level)
+	- ‘cd /../../..’ (can give a path)
+- ‘clear’ (clears the screen without deleting)
+- ‘mkdir’ <directory name> (makes directories)
+- ‘which’ <program> (tells you where program lives on machine/if it has it)
+- ‘curl’ -O -k <URL> (download files/ignores certificates/with the same name)
+- ‘man’ <program> (brings you to manual page)
+- ‘less’ <filename> (new version of more/lets you view file)
+- ‘tar’ xzf <filename> (extract a file in gzip format)
+- ‘find’ (will show every file in that level of directory)
+
+#### Directory structure Linux
+-	Starts with a leading / (can cd to /)
+-	Bin is below / (binary – executables live here)
+-	Lib is below / (library – support files)
+-	Home is below / 
+-	Below home is our account where we can make files and directories
+
+#### Setting up CS340 directory 
+-	Use mkdir CS340 in your Linux lab directory
+-	Enter CS340
+##### Scraping from the internet
+o	Use curl and a URL to download random.tar.gz
+
+#### How to use less and the man pages 
+-	Options are the flags that we use with commands to make them do things
+-	/ allows you to type and hit enter to search 
+-	Man gets you to the manual
+-	Less allows you to view files
+-	Get out of less with q
+
+
+
+#### How to use for loops in bash
+	###### Example 1
+	```
+	for I in {0..100}
+		do
+		echo  $i
+		done
+	```
+	###### Example 2
+		Stepping through by 2’s
+	```
+	for I in {0..100..2}
+		do
+		echo  $i
+		done
+	```
+
+
+
+