https://homeostasis.scs.carleton.ca/wiki/index.php?action=history&feed=atom&title=Operating_Systems_2021F_Lecture_10 2026-04-06T04:46:31Z Revision history for this page on the wiki MediaWiki 1.42.1 https://homeostasis.scs.carleton.ca/wiki/index.php?title=Operating_Systems_2021F_Lecture_10&diff=23402&oldid=prev 2021-10-12T17:09:20Z

<p>Created page with &quot;==Video== Video from the lecture given on October 12, 2021 is now available: * [https://homeostasis.scs.carleton.ca/~soma/os-2021f/lectures/comp3000-2021f-lec10-20211012.m4v...&quot;</p> <p><b>New page</b></p><div>==Video==<br /> <br /> Video from the lecture given on October 12, 2021 is now available:<br /> * [https://homeostasis.scs.carleton.ca/~soma/os-2021f/lectures/comp3000-2021f-lec10-20211012.m4v video]<br /> * [https://homeostasis.scs.carleton.ca/~soma/os-2021f/lectures/comp3000-2021f-lec10-20211012.cc.vtt auto-generated captions]<br /> Video is also available through Brightspace (Resources-&gt;Class zoom meetings-&gt;Cloud Recordings tab)<br /> <br /> ==Notes==<br /> <br /> &lt;pre&gt;<br /> Lecture 10<br /> ----------<br /> <br /> Requests<br /> - A2: 2, 3, 5, 9<br /> <br /> Yes, *please* use the code and tools from the tutorials on the assignments. That&#039;s the purpose of the tutorials!<br /> <br /> remember . refers to the current director, .. refers to the parent directory, always<br /> <br /> In real code, you&#039;d normally use getopt and getenv rather than parse_args and find_env (because the library versions are more robust and offer more features), but you *can* parse command line arguments and environment variables yourself.<br /> <br /> Remember NULL in C can be assigned to any pointer, it means<br /> the zero pointer which stands for an invalid pointer<br /> - no way to point to address 0<br /> - &#039;\0&#039; is kind of the same thing, but you&#039;d have to<br /> cast it to a pointer. You never have to cast NULL<br /> <br /> What is the difference between a script and a program?<br /> - both can be run with execve<br /> - but, with a binary program, just the code of the<br /> program is loaded into the process<br /> - with a script, an interpreter is specified in the first line<br /> with #!, *that* is the program that is loaded, and it is<br /> given an argument, the script to run<br /> <br /> Note that with killsnoop, we&#039;re only seeing calls to the kill system call<br /> - many signals are generated by the kernel without going through kill (the kernel doesn&#039;t need to make a system call itself to do something)<br /> - e.g., SIGCHLD<br /> <br /> So programs don&#039;t have to turn keystrokes into signals<br /> - they can just parse it<br /> - top has set its own handlers for control characters<br /> - so Ctrl-C doesn&#039;t generate a signal<br /> <br /> In userspace, to send a signal you use the kill system call<br /> - but the kernel uses signals for other things<br /> <br /> in killsnoop<br /> - PID is the process sending the signal<br /> - TPID is the process that will receive the signal<br /> T = target<br /> &lt;/pre&gt;</div>

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