Operating Systems 2019W Lecture 3 - Revision history

Soma: /* crash.c */

2019-01-14T23:46:56Z

crash.c

← Older revision		Revision as of 23:46, 14 January 2019
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	return 0;		return 0;
	}		}
	</~~listing~~>		</source>

Soma: /* crash.c */

2019-01-14T23:46:26Z

crash.c

← Older revision		Revision as of 23:46, 14 January 2019
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	===crash.c===		===crash.c===

	<~~listing~~ lang="c">		<source lang="c" line>
	#include <stdio.h>		#include <stdio.h>

Soma at 23:45, 14 January 2019

2019-01-14T23:45:46Z

← Older revision		Revision as of 23:45, 14 January 2019
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	==Notes==		==Notes==

			===In Class===
			<pre>
			Lecture 3
			---------
			* tutorials have started
			* look in cuLearn to see your TA
			- in grades, "TA" (feedback)

			* system calls!

			- we have processes
			- they are isolated (only have a virtual CPU and virtual memory)
			- to access any other resources, it must make a system call
			- system calls are requests to the kernel
			- kernel decides whether a system call is allowed or not based on
			the user and group of the process


			- file system calls
			open, read, write, lseek, (mmap), close

			Question
			- why do we only need to do GET, POST on the web, but we need to
			do a open before a read or write?

			HTTP is (originally) stateless
			- server doesn't have to remember client state between requests

			UNIX file API is stateful
			- maintains state between requests

			file descriptors are an index into an array of file state maintained by the kernel for each process

			---break---

			SCS sysadmin in charge of openstack: Andrew Pullin

			Processes can use file descriptors that were opened by "someone else"
			- parent process
			- "the one who execve'd me"

			FORK:
			process 4500
			- opens file on fd 7
			- runs fork, gets 4501

			process 4501
			- identical to 4500
			- so has fd 7


			EXECVE

			process 5000
			running /bin/bash
			- opens file on fd 1
			execve("/bin/ls")
			- fd 1 still open for ls (running as process 5000)
			</pre>

			==Code==

			===crash.c===

			<listing lang="c">
			#include <stdio.h>

			int main(int argc, char *argv[])
			{
			int *x;

			x = (int *) 0;

			*x = 5;

			printf("Done!\n");

			return 0;
			}
			</listing>

Soma: Created page with "==Video== Video from the lecture given on January 14, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019w/lectures/comp3000-2019w-lec03-20190114.m4v is now available]...."

2019-01-14T23:37:07Z

Created page with "==Video== Video from the lecture given on January 14, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019w/lectures/comp3000-2019w-lec03-20190114.m4v is now available]...."

New page

==Video==

Video from the lecture given on January 14, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019w/lectures/comp3000-2019w-lec03-20190114.m4v is now available].

==Notes==