R.samanfar at 23:14, 1 October 2018

2018-10-01T23:14:01Z

← Older revision		Revision as of 23:14, 1 October 2018
Line 8:		Line 8:

	==Notes==		==Notes==

	===Notes on Tutorial 2===		===Notes on Tutorial 2===

	'''Q6:''' Make the shell output "Ouch!" when you send it a SIGUSR1 signal.		'''Q6:''' Make the shell output "Ouch!" when you send it a SIGUSR1 signal.
	*To test, send a signal to a process		*To test, send a signal to a process
Line 34:		Line 36:
	*Solutions will be posted and discussed in class Sept 26th		*Solutions will be posted and discussed in class Sept 26th
	===Class Notes===		===Class Notes===

	*Signals:		*Signals:
	**is a message sent to a process		**is a message sent to a process
Line 73:		Line 76:
	**the shell makes sure that file descriptors 0,1,2 are open and are going somewhere valid		**the shell makes sure that file descriptors 0,1,2 are open and are going somewhere valid
	===Useful Commands/examples===		===Useful Commands/examples===

	*envp – came from main, can be changed by putenv		*envp – came from main, can be changed by putenv
	*ls /proc		*ls /proc

R.samanfar: /* Notes */

2018-10-01T23:12:33Z

Notes

← Older revision		Revision as of 23:12, 1 October 2018
Line 8:		Line 8:

	==Notes==		==Notes==
			===Notes on Tutorial 2===
			'''Q6:''' Make the shell output "Ouch!" when you send it a SIGUSR1 signal.
			*To test, send a signal to a process
			*Use kill command
			**kill -<SIGNALNAME> <PID>
			**ex: kill -USR1 4094
			'''Q8:''' Replace the use of find_env() with getenv(). How do their interfaces differ?
			*How are the parameters/arguments different
			*Look at man pages for getenv()
			*Different number of arguments
			*Why does getenv() not need the environment to be passed in
			** It has it already
			**#man pages, see also, environ is user environment global variable defined by standard library
			*#Longer answer: we got the environment variable from main as an argument (envp[])
			'''Q9:''' Use putenv() to implement LASTCOMMAND from Tutorial 1.
			*putenv() handles variables for you
			*Allows you to define environment variables and add it
			*Only changes for current process
			**To change for another process, fork and use execve
			===Notes on Assignment 1 ===
			*Not finalized = “not completely debugged”
			*Due Sept 26th 2:30pm
			*Based on tutorials
			*Question 9 looking at man page for execve can get an answer- not what he’s talking about, he wants experimental evidence
			*Solutions will be posted and discussed in class Sept 26th
			===Class Notes===
			*Signals:
			**is a message sent to a process
			**some can be blocked until unblocked
			**SIGKILL and SIGSTOP cannot be caught, blocked or ignored
			**Handlers respond to specific signals
			***Interrupts what’s currently happening
			***Can cause jumps that happen randomly in your program
			***You don’t know the state of the program when a signal handler executes
			***Kernel calls a function
			***Don’t try to handle a signal in a signal handler, generally block them in a handler
			***If you don’t define a signal handler, there is a default handler that will run
			**No signal handler for SIGKILL or SIGSTOP
			**Can run strace on kill signal
			***Does kill system call
			***Takes a process id and a signal
			*I/O redirection:
			**changing which file things get written to
			**ls > foo.txt
			***foo.txt contains the contents that ls outputted
			***'''>''' send output to foo.txt
			***ls does not know about redirection
			***ls should send it is output to foo.txt
			***ls without redirection is already outputting to a file (standard output- file descriptor 1)
			****standard out sends information to a file
			****fprintf – goes to file descriptor 2
			****printf – goes to file descriptor 1
			**ps aux
			***shows you what’s running and what terminal it is connected to (tty2, ?, pts/0)
			****pts/0 – sudo terminal
			****tty1 – used to run log in
			***terminal usually referred to as tty (teletype, screen and keyboard, connects to another computer)
			*File descriptors
			**a number associated with an open file
			**each process has its own file descriptor
			**first file opened is assigned file descriptor 0
			**stored on the kernel
			**by default in linux there are file descriptors for every program
			**the shell makes sure that file descriptors 0,1,2 are open and are going somewhere valid
			===Useful Commands/examples===
			*envp – came from main, can be changed by putenv
			*ls /proc
			**Tells you information on all the running processes
			**Can cd into a process id directory
			***fd – file descriptor directory
			***ex: /proc/1973/fd
			**echo $TERM
			**tells you what terminal you are using
			**TERM is an environment variable
			*cd /dev
			**can see all of the special files
			**b – block devices
			**c – character devices
			*echo hello > 0
			*echo hello > 1
			**run in one terminal, can write to file displayed in another terminal
			**numbers correspond to different terminals being used
			**if you have permission you can write to them (other users would not be allowed)
			*echo hello > test1
			**to the shell, please open the file test1 for writing, open it on file descriptor 1, the process will then do an execve of echo
			**cat test -> results in “hello”
			*cat 333shell.c \| sort
			**vertical bar is a pipe
			**whatever is written by cat will be read by sort
			**pairing of file descriptors
			**sorted all the lines of the program
			*pstree
			**displays the tree of all running processes

Soma: Created page with "==Video== Video from the lecture given on September 19, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec05-20180919.m4a is now available]...."

2018-09-19T20:29:04Z

Created page with "==Video== Video from the lecture given on September 19, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec05-20180919.m4a is now available]...."

New page

==Video==

Video from the lecture given on September 19, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec05-20180919.m4a is now available].

==Code==

Code and files from the lecture (captured as they were at the end) are available [https://homeostasis.scs.carleton.ca/~soma/os-2018f/code/lec05/ here].

==Notes==

Operating Systems 2018F Lecture 5 - Revision history

R.samanfar at 23:14, 1 October 2018

R.samanfar: /* Notes */

Soma: Created page with "==Video== Video from the lecture given on September 19, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec05-20180919.m4a is now available]...."