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Lecture 02 - February 05, 2002
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AGENDA:
0 Admin
1 P1 - Command interpreter implementation
2 Ch. 1 highlights

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0 - ADMIN
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Quiz #1 on Friday.

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1 - P1: COMMAND INTERPRETER IMPLEMENTATION
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Ch 1.3 and 1.4 cover many relevant details. Be sure to
  do the reading!

Discuss implementation of command interpreter (shell)
* main( int argc, char *argv[] )
* Tanenbaum covers fork, but it's worth getting this
    right.
  Run "man fork"

  cpid = fork();
  if cpid == -1 => oops, fork failed. Look out below
  if cpid == 0  => this is the child process
  if cpid >  0  => this is the parent process and cpid
     is the process id of the child

* execvp( what_to_exec, new_proc_argv )
  print an error message, then exit right below execvp
  - if execvp works, never reaches message and exit
  - if execvp fails, you DO NOT want the child process
    to stay alive and start acting like the parent.
    That's the situation that leads to great
    unhappiness.

* Tanenbaum discusses waitpid and gives examples
  p. 24, fig 1-10; p. 25

Go through samples in the p1 dir & discuss coding style
  and the use of seatbelts when doing system 
  programming.
When it comes to grading, I want to see that you check
  EVERY system/library call for possible failure.


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2 - CH. 1 HIGHLIGHTS
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multiprogramming: 1st step toward timesharing
spooling: manage I/O transfers by collecting data
  in a file while other things continue to run on
  the system
timesharing: multiple users with on-line terminals
MULTICS: grandparent of pretty much all modern O/S's.
Version 7 UNIX: one of the first major widely-used
  versions of UNIX
POSIX: a POrtable Standard for unIX (or something like
  that -- it's been a long time) that was meant to
  make it possible for all UNIX clones to be compatible
  in all the important aspects
LINUX: the product of enthusiastic people who wanted
  to make MINIX "bigger and better (well, at least
  bigger)" (p. 15).

address space: a list of memory locations available
  to a process
core image: an image of a process
signal: a message that causes a process to put
  everything on hold and run a special signal-handling
  procedure. What happens depends on the signal and
  the programming.  Try "kill -l" to list signals
  available on a UNIX system.
UID: user id
super-user: system omnipotent account

root directory: top level directory
rwx bits: do an "ls -l" to demonstrate briefly
file descriptor: discuss
root file system: fig 1-7 p. 19
special files: block special files, character special
  files
pipe: pseudofile buffer that allows processes to write
  to each other

system calls: look through fig 1-9 p. 23
COS 421 - Lecture Notes #2		SPRING 2003	
COS421-lect-2003-02-05.doc	Page 2	Printed 05.02.03