https://homeostasis.scs.carleton.ca/wiki/index.php?action=history&feed=atom&title=Operating_Systems_2020W_Lecture_13 2026-06-02T22:26:50Z Revision history for this page on the wiki MediaWiki 1.42.1 https://homeostasis.scs.carleton.ca/wiki/index.php?title=Operating_Systems_2020W_Lecture_13&diff=22578&oldid=prev 2020-03-20T02:34:58Z

<p>Created page with &quot;==Video== Video from the lecture given on February 26, 2020 [https://homeostasis.scs.carleton.ca/~soma/os-2020w/lectures/comp3000-2020w-lec13-20200226.m4v is now available]....&quot;</p> <p><b>New page</b></p><div>==Video==<br /> <br /> Video from the lecture given on February 26, 2020 [https://homeostasis.scs.carleton.ca/~soma/os-2020w/lectures/comp3000-2020w-lec13-20200226.m4v is now available].<br /> <br /> ==Notes==<br /> <br /> &lt;pre&gt;<br /> Lecture 13 - midterm review!<br /> ----------------------------<br /> poll posted on running native Linux<br /> <br /> Topics:<br /> - assignment 2 solutions<br /> - key concepts<br /> - your questions!<br /> <br /> THE TEXTBOOK IS HELPFUL TO REVIEW<br /> - it helps with the concepts!<br /> - but emphasis is different, so use it selectively<br /> - not all concepts are in the textbook<br /> <br /> Concepts relevant to midterm:<br /> - OS kernel<br /> - user mode/supervisor mode<br /> - root user/unprivileged users<br /> - uid, gid, euid, egid, username, groups<br /> - file permissions: user, group, other, read, write, execute<br /> - types of files: regular files, directories, symbolic links, block devices,<br /> character devices<br /> - hard links<br /> - setuid bit, setgid bit<br /> - why are programs setuid root?<br /> - how does this interact with uid, euid of a process<br /> (after execve of a setuid root process)?<br /> - logical vs physical sizes of files<br /> - relationship between shell operators (&gt;, &lt;) for redirecting standard input, output and underlying system calls, file descriptors<br /> - connection with open, dup2<br /> - relationship between execve, command line arguments, environment variables<br /> - login shells, how only some programs are allowed to be shells<br /> (and what changing the login shell changes for a user)<br /> - ssh key-based authentication<br /> - identity keys (local) vs authorized_keys<br /> - known_hosts (remote host public keys stored locally)<br /> - how to enable public key auth for a user<br /> - how hosts are identified using their public keys<br /> - running commands on remote hosts via ssh<br /> - runs them via a shell<br /> - why do that versus just do an execve<br /> - stat vs lstat vs fstat<br /> - using file descriptors versus filenames<br /> - following or not following symlinks<br /> - info returned (all the inode metadata)<br /> - deleting a file is just unlinking (every regular file is a hard link)<br /> - link count for an inode<br /> - copying vs making a hard link vs making a symbolic link<br /> - when does the inode stay the same versus change<br /> - if you delete one, how does it affect the other<br /> (A hardlinked to B, delete A versus<br /> A symlinked to B, delete A)<br /> - holes in files<br /> - how seeking + writing past end of file will create them<br /> - effect on logical vs physical size of a file<br /> - filesystem structure: inodes, directories, superblocks<br /> - role of lost+found, fsck, mkfs<br /> - sshfs<br /> - how its weirdness relates to restrictions on userspace programs,<br /> remote hosts (with different uid/gid mappings)<br /> - tty&#039;s, pseudo tty&#039;s (/dev/tty1, /dev/pts/0)<br /> - as character devices<br /> - relationship to standard in/out/error for interactive programs<br /> - local vs global variables in C<br /> - difference between function calls, library calls, system calls<br /> - library calls are dynamically linked functions<br /> - basic idea of dynamic linking<br /> - how shells find external programs<br /> - PATH environment variable<br /> - process termination (exit system call, signals)<br /> - process return values &amp; wait system call<br /> - fork, execve<br /> - role in running external commands in the shell<br /> - signal handlers<br /> - registering<br /> - when called<br /> - concurrency<br /> <br /> Concepts not so relevant for midterm (but will come up later):<br /> - secure hashes<br /> - pipes<br /> - gdb, strace<br /> - but should know things you could only learn by using those tools<br /> - exact details of structure of ext4<br /> - CPU registers, stack vs heap<br /> <br /> Requested clarifications<br /> - uid vs euid<br /> - inodes<br /> - hard links<br /> &lt;/pre&gt;</div>

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