COMP 3000 2012 Week 5 Notes

Processes

• how a process starts
  • fork()
    • creates a new process
    • creates own distinct address space
    • different return values for parent and child
    • copies state, doesn't share
    • modern unix doesn't actually copy, it just pretends that it copies
      • "[...] which is the story of virtual memory." -Anil
  • execve(const char *path, char *const argv[], char *const envp[])
    • when a process runs execve, it commits suicide and hands its process over to the new execution
    • note that the arrays themselves are null terminated
    • copies state, doesn't share
    • envp are environment variables
    • file descriptors stay open
      • so if you redirect file descriptors for original process, they stay redirected
    • env
      • command that dumps environment variables
• how a process ends
  • exit(int return)
    • zero is normal exit
    • non-zero is abnormal
    • magic! see: source for exit(int) in minix
  • wait(int* stat_loc)
    • blocks until a child terminates
  • waitpid(pid_t pid, int* stat_loc, int options)
    • blocks until child with given pid (process id) terminates
• process information
  • compare the output of strace and ltrace
    • tells you what the library is doing before it gets to the system level
• system calls
  • open
    • creates a file descriptor
  • close
  • read
  • write
  • seek
  • chown
    • the chgrp command uses the lchown system call
  • chmod
  • unlink
  • mmap
    • map to memory
    • forward reference to the story of virtual memory