Computer Science 432 Operating Systems Williams College Fall 2006

Agenda

• Announcements
  • No colloquium this week - instead, pumpkin carving
• Exam Submission
• Unix Systems Programming
  • Error checking and reporting
    • always check return values of system calls!
    • errno variable
    • perror(3), strerror(3)
  • Process management
    • PID queries: getpid(2), getppid(2)
    • Process creation: fork(2), vfork(2)
    • Process termination: exit(3), _exit(2)
    • Parent notification: wait(2), waitpid(2)
  • Starting new programs - exec system calls
    • To fork(2) anything but a copy of yourself...
    • execl(3), execv(3), execlp(3), execvp(3)
    • varags vs. arrays, search path or not?
  • Signals
    • Interprocess communication mechanism
    • kill -l to list signal types
    • kill -SIGNAL pid to send a signal to a process
    • Every process has signal handlers - react to signals sent to the process.
    • A default signal handler is attached when a process is created
    • signal(3) replaces signal handler
      • custom function
      • SIG_IGN, SIG_DFL
    • setitimer(2) to set alarm to deliver SIGALRM
    • kill(2) sends signals from a program
  • Low-level file operations
    • C stdio routines (printf and friends) are fairly high level
    • low-level operations: open(2), close(2), read(2), write(2)
    • work with file descriptors
  • Pipes
    • Another interprocess communication mechanism
    • Powerful command-line tool: |
    • Unnamed pipe created with pipe(2)
      • fd[0] is the "read end", fd[1] is the "write end"
      • these are file descriptors
    • Named pipe created with mkfifo(1) or mkfifo(2)
      • part of the file system
  • Duplicating file descriptors
    • dup2(2): reroute things intended for one file descriptor to another
    • redirect existing file descriptors (0=stdin, 1=stdout, 2=stderr)
    • hook the output of one pipe to the input of another
  • Other useful C tips and tricks
    • gcc -Wall
    • debuggers: gdb, ddd, Totalview (Linux cluster)
    • initialization of memory (or not)
    • string manipulation: see string(3)
    • memory management: malloc(3), free(3) - no garbage collector here!
    • "object oriented" C programming
• Lab 5 Out

Lecture Assignment

No new lecture assignment due for next time. Recover from the exam, get started on the new lab.

The readings for next time are SG&G Chapter 7.

Examples

• perror
• exec
• signals
• everyother
• pipes