CSC209: Administrivia Software Tools and Systems Programming
Richard Krueger Email : [e-mail] Office hours: BA 3234
Email: [e-mail]
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More on email
Not helpful
I used the makefile you gave us, but my program doesn't compile. What could be wrong?" My program gets a seg fault error message, but I don't know why.
Course Information
Check the course information sheet (handed out and on the course web page) for
Office hours Contact information Assignment schedule
Much better
When I compile my program, I get the following error message. It seems to indicate that there is a problem with the following lines of code. (cut and paste error messages and code.) The debugger tells me that the seg fault I'm getting is on the following line. I don't see what the problem is with this line. (file included below)
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The course web page is the official source of announcements.
http://www.cs.utoronto.ca/~csc209h/
Make sure you have the prerequisites!
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Assignments
A1: Shell programming (Bourne shell) A2: Manipulating files and directories (in C) A3: Processes (in C) A4: Sockets (in C) The assignments are best done over a couple of weeks, a few hours at a time. All code must work on the CDF servers to receive full marks. Don't wait until the last day!
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Submitting Assignments
You will be using CVS to manage and submit your assignments. The repositories will be set up this week. You should start learning how to use it as soon as possible. Do not wait until the last minute to try to commit your assignment for the first time. This week's tutorial will cover using CVS. See web page for tutorial information.
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Plagiarism
"The work you submit must be your own, done without participation by others. It is an academic offense to hand in anything written by someone else without acknowledgement." You are not helping your friend when you give him or her a copy of your assignment. You are hurting your friend when you ask him or her to give you a copy of their assignment.
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What is cheating?
Cheating is
copying parts or all of another student's assignment including code from books, web sites, other courses without attribution getting someone else to do substantial parts of your assignment giving someone else your solution
Cheating is not
helping to find a bug in a friend's code (be careful) helping each other understand man pages or 8 example code.
The Big Picture (in Java)
Source code file
Hw.java
FODVV+Z^ SXEOLFVWDWLFYRLG PDLQ6WULQJ>@DUJV^ VRSULQWOQ+HOOR ` `
The Big Picture
Source code file
hw.c
LQFOXGHVWGLRK! YRLG
Compile it
Object file
Hw.class
Compile it
hw
Object file
% javac Hw.java
PDLQ ^ SULQWI+HOORZRUOG `
% gcc o hw hw.c
Run it in VM % java Hw
Process
Run it % hw
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Process
90 +Z
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Source Code Files
hw.c
LQFOXGHVWGLRK! YRLG PDLQ ^ SULQWI+HOORZRUOG `
Compiling a program
% gcc o hw hw.c
What is a file? How does the system know where to find hw.c? What is the meaning of #include<stdio.h> ? What does printf really do?
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A compiler is a program translates source code into object (machine) code. Here we are running the compiler at the command line. A shell is a program that can execute another program.
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Shells
% gcc o hw hw.c
Object Files/Executables
high address
The % is a shell prompt. Shells
accept commands (programs) as input finds the executable interprets the arguments starts executing the command
stack
Typical memory layout of programs.
sp (stack pointer)
Process control block (PCB)
pc (program counter)
heap uninit. data init. data text
low address
...
Shells also have some "built-in" commands.
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Running a program
% gcc o hw hw.c % hw
Processes
A process is an executing instance of a program. The OS keeps track of information about the process.
process ID a unique non-negative integer process state "running", "ready", "blocked" program counter which instruction is being executed. a list of open files etc.
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load a program into memory and hand it off to the OS to run the program.
A different big picture
sh less vi perl gcc nedit grep ddd
Course Overview
Software Tools
Understanding the shell Shell programming
libc C Interface to Unix system services
Systems Programming
Unix system services Unix kernel (in C) computer
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C files processes concurrency communication
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Self Study Topics
Using CVS - some tutorial coverage Using Unix - some coverage tutorial Learning an editor nedit, vi, emacs Learning a debugger ddd is the easiest Readings
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Unix History
Inspired by Ken Thompson to play Space Travel on his DEC PDP-7 in 1969. Thompson wrote the first version of Unix in assembler in one month. Dennis Ritchie and Ken Thompson ported an enhanced version to a PDP-11/20 in 1970. Ritchie and Rudd Canaday ported a cut down version of the BCPL language to Unix, calling it B. The PDP-11 was purchased for text processing. The first user was Bell's Patent Department. Pipes and C were added in 1971-73
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More Unix History
BTL Lawyers, "License to universities, but no support." This led to extensive sharing. University of Toronto on the first mailing list in 1975. Software Tools User Group formed in 1978. Canadian connection!
Bill Reeves, Brian Kernighan, Rob Pike...
Why Unix?
Available on a number of platforms. Multi-user, multi-programmed. Shares computer resources sensibly. Permits manipulation of files, processes, and programs. Allows inter-process and inter-machine communication. Permits access to its operating features.
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Berkeley Software Distribution grew out of collecting and distributing bug fixes. (Led to FreeBSD, NetBSD) Bill Joy started at Berkeley but joined the startup Sun Microsystems in 1982. 1991, Linus Torvalds posts a note describing his experimental OS modeled on minix.
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The Unix Philosophy
Write programs that do one thing and do it well. Write programs to work together. Write programs that handle text streams, because that is a universal interface.
Files and Directories
"Everything is a file." Unix provides a file interface for all Input/Output.
regular files directories devices
video (block) keyboard (character) sound (audio) network (block)
Try ls l /dev and look at the permissions string. crw------brw------c = character, b = block
File interface = open, read, write, close
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File System Hierarchy
Everything starts in the "root" directory whose name is "/" A directory is a file that contains directory entries. (Ch 4.3) A directory entry maps a file name to an inode. An inode is the data structure that contains information about a file, including which disk blocks contain the file data.
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File System Hierarchy
/ hard link u u1 h u2 bin usr lib
u3
csc209h symbolic links krueger
F
c4reidka
Use df to see all the different disk partitions on CDF.
IDOO SXE UHSR
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File Systems and Links
One file system per disk partition. A file system can be mounted at any point in the directory tree of another file system. An entry in a directory file which specifies an inode is a hard link. There can be several hard links to a file, but hard links cannot cross file systems. A soft link (symbolic link) is a small file containing t...